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1.  Atazanavir Pharmacokinetics With and Without Tenofovir during Pregnancy 
Background
Plasma concentrations of several protease inhibitors are decreased during pregnancy. Few data are available describing atazanavir exposure during pregnancy, especially when used in combination with tenofovir, whose coadministration with atazanavir results in decreased atazanavir exposure.
Design
IMPAACT 1026s is an on-going, prospective, non-blinded study of antiretroviral pharmacokinetics in HIV-infected pregnant women that included two cohorts receiving atazanavir/ritonavir 300mg/100mg once daily during the third trimester through 6-12 weeks postpartum either with or without tenofovir.
Methods
Intensive steady-state 24-hour pharmacokinetic profiles were performed during the third trimester and at 6-12 weeks postpartum. Atazanavir was measured by reverse-phase HPLC with a detection limit of 0.13 mcg/mL. Pharmacokinetic targets were the estimated 10th percentile atazanavir AUC (29.4 mcg*hr/mL) in non-pregnant historical controls taking the standard dose (mean AUC=57 mcg*hr/mL) and a trough concentration of 0.15 mcg/mL, the concentration target used in therapeutic drug monitoring programs. Infant bilirubin concentrations were measured at 24-48 hours and 4-6 days after birth.
Results
Atazanavir pharmacokinetic data were available for 38 women (18 without tenofovir, 20 with tenofovir. Median atazanavir AUC was reduced during the third trimester compared to postpartum for subjects not receiving tenofovir (41.9 vs 57.9 mcg*hr/mL, p=.02) and for subjects receiving tenofovir (28.8 vs. 39.6 mcg*hr/mL, p=.04). During the third trimester, AUC was below the target in 33% (6/18) of women not receiving tenofovir and 55% (11/20) of women receiving tenofovir. Trough concentration was below the target in 6% (1/18) of women not receiving tenofovir and 15% (3/20) of women receiving tenofovir. The median (range) ratio of cord blood/maternal atazanavir concentration in 29 paired samples was 0.18 (0 - 0.45). No excessive infant bilirubin concentrations were observed.
Conclusions
Atazanavir exposure is reduced by pregnancy and by concomitant tenofovir use. A dose increase of atazanavir/ritonavir to 400mg/100mg may be necessary in pregnant women to ensure atazanavir exposure equivalent to that seen in nonpregnant adults, especially for pregnant women who are antiretroviral-experienced and/or who are also receiving tenofovir.
doi:10.1097/QAI.0b013e31820fd093
PMCID: PMC3125419  PMID: 21283017
atazanavir; tenofovir; pharmacokinetics; pregnancy; HIV; mother to child transmission
2.  Pharmacokinetics and Tolerability of Daptomycin at Doses up to 12 Milligrams per Kilogram of Body Weight Once Daily in Healthy Volunteers 
Antimicrobial Agents and Chemotherapy  2006;50(10):3245-3249.
Daptomycin, a novel lipopeptide, is bactericidal against a broad range of gram-positive strains, including methicillin- (MRSA) and vancomycin-resistant Staphylococcus aureus. Daptomycin is approved at 4 mg/kg of body weight given intravenously once daily for the treatment of complicated skin and skin structure infections and at 6 mg/kg for the treatment of S. aureus bloodstream infections (bacteremia), including right-sided endocarditis caused by methicillin-susceptible S. aureus and MRSA. The present study was designed to evaluate the multiple-dose pharmacokinetics and safety of daptomycin at doses of 6 to 12 mg/kg in healthy volunteers. Three cohorts of 12 subjects each were given daptomycin (10 mg/kg) or placebo once daily for 14 days, daptomycin (12 mg/kg) or placebo once daily for 14 days, or daptomycin (6 or 8 mg/kg) once daily for 4 days. Daptomycin produced dose-proportional increases in the area under the plasma concentration-time curve and in trough daptomycin levels and nearly dose-proportional increases in peak daptomycin concentrations. Other pharmacokinetic parameters measured on day 1 and at steady state were independent of the dose, including the half-life (approximately 8 h), weight-normalized plasma clearance (9 to 10 ml/h/kg), and volume of distribution (approximately 100 ml/kg). Plasma protein binding was 90% to 93% and was independent of the daptomycin concentration. Daptomycin did not produce electrocardiographic abnormalities or electrophysiological evidence of muscle or nerve toxicity. Daptomycin was well tolerated in subjects dosed with up to 12 mg/kg intravenously for 14 days. Doses of daptomycin higher than 6 mg/kg once daily may be considered in further studies to evaluate the safety and efficacy of daptomycin in difficult-to-treat infections.
doi:10.1128/AAC.00247-06
PMCID: PMC1610083  PMID: 17005801
3.  Single-dose daptomycin pharmacokinetics in chronic haemodialysis patients 
Nephrology Dialysis Transplantation  2009;25(4):1279-1284.
Background. Daptomycin has concentration-dependent antibacterial activity against Gram-positive bacteria. Its use is increasing in haemodialysis units. The manufacturer recommends a 4–6-mg/kg dose administered every 48 hrs for patients receiving haemodialysis. However, there are no published data about daptomycin pharmacokinetics and clearance during haemodialysis. The recommended dosing regimen would conflict with asymmetric thrice-weekly haemodialysis, which yields two ~44-hr and one ~68-hr interdialytic periods. This is the first study to evaluate daptomycin pharmacokinetics in haemodialysis patients, assess the extent of daptomycin dialytic removal and model serum concentrations at 44 and 68 hrs.
Methods. Six otherwise healthy subjects on chronic haemodialysis (55.3 ± 16.1 years old, three females, 66.2 ± 14.2 kg) received a single 6-mg/kg dose of daptomycin post-haemodialysis infused over 30 minutes. Serial blood samples were collected for ~44 hrs (pre-next haemodialysis) and throughout the subsequent haemodialysis session with a high permeability haemodialyser. Individual pharmacokinetic parameters determined by compartmental analysis were used to model trough serum concentrations at 44 and 68 hrs with 6-, 8- and 10-mg/kg post-haemodialysis doses.
Results. The haemodialysis session in this trial yielded mean urea and daptomycin reduction ratios of 79.6 ± 5.8% and 57.6 ± 9.2%, respectively. Daptomycin half-life was 19.4 ± 6.5 and 3.8 ± 1.1 hrs ‘off’ and ‘on haemodialysis’, respectively, with minimal rebound 1 hr post-haemodialysis. All modelled trough concentrations at 44 and 68 hrs at all doses exceed typical minimum inhibitory concentration (MIC90) values for Staphylococcus aureus and Enterococcus faecalis.
Conclusions. Daptomycin serum concentrations declined by ~50% after a 4-hr haemodialysis session with a high permeability haemodialyser. A 6-mg/kg i.v. post-haemodialysis thrice-weekly dose should result in sufficient pre-haemodialysis daptomycin serum concentrations even after a 68-hr interdialytic period.
doi:10.1093/ndt/gfp655
PMCID: PMC2902860  PMID: 20007981
daptomycin; Gram-positive bacteria; haemodialysis; pharmacokinetics
4.  Efficacy of Daptomycin in Experimental Endocarditis Due to Methicillin-Resistant Staphylococcus aureus 
Methicillin-resistant Staphylococcus aureus is becoming increasingly prevalent as both a nosocomial and a community-acquired pathogen. Daptomycin, a lipopeptide antibiotic now in phase III clinical trials, is rapidly bactericidal in vitro against a range of gram-positive organisms, including methicillin-resistant S. aureus (MRSA). In this study, we compared the efficacy of daptomycin with that of vancomycin, each with or without rifampin, in a model of experimental aortic valve endocarditis due to MRSA. The infecting strain (MRSA strain 32) was susceptible to daptomycin (MIC = 1 μg/ml), vancomycin (MIC = 0.5 μg/ml), and rifampin (MIC = 0.5 μg/ml). Daptomycin was administered at 25 or 40 mg/kg q24h (q24h) by subcutaneous injection in an attempt to simulate human doses of 4 and 6 mg/kg q24h, respectively. Vancomycin was given at 150 mg/kg q24h by continuous intravenous infusion. Rifampin was given at 25 mg/kg by intramuscular injection q24h. Treatment was started 6 h postinoculation and continued for 4.5 days. Outcome was assessed by counting the residual viable bacteria in vegetations. The mean peak daptomycin levels in serum at 2 h after subcutaneous administration of 25 and 40 mg/kg were 64 and 91 μg/ml, respectively. Daptomycin was undetectable in serum at 24 h. The total exposure was comparable to that achieved clinically in humans receiving the drug. Bacterial counts (mean log10 number of CFU per gram ± the standard deviation) in untreated controls reached 10.6 ± 0.8. In treated rats, bacterial counts were as follows: vancomycin, 7.1 ± 2.5; daptomycin at 25 mg/kg, 5.5 ± 1.7; daptomycin at 40 mg/kg, 4.2 ± 1.5. The difference between daptomycin at 40 mg/kg and vancomycin at 150 mg/kg was statistically significant (P = 0.004). In the study of combination therapy, vegetation bacterial counts were as follows: daptomycin at 40 mg/kg, 4.6 ± 1.6; rifampin, 3.6 ± 1.3; vancomycin plus rifampin, 3.3 ± 1.1; daptomycin plus rifampin, 2.9 ± 0.8. The difference between daptomycin and daptomycin plus rifampin was statistically significant (P = 0.006). These results support the continued evaluation of daptomycin for serious MRSA infections, including infective endocarditis.
doi:10.1128/AAC.47.5.1714-1718.2003
PMCID: PMC153308  PMID: 12709345
5.  Efavirenz Pharmacokinetics during the Third Trimester of Pregnancy and Postpartum 
Background
The impact of pregnancy on efavirenz pharmacokinetics is unknown.
Methods
International Maternal Pediatric Adolescent AIDS Clinical Trials (IMPAACT) P1026s is an on-going, prospective, non-blinded study of antiretroviral pharmacokinetics in HIV-infected pregnant women that included a cohort receiving 600 mg efavirenz once daily as part of combination antiretroviral therapy. Intensive steady-state 24-hour blood sampling was performed during the third trimester and at 6–12 weeks postpartum. Maternal and umbilical cord blood samples were drawn at delivery. Pharmacokinetics targets were the estimated 10th percentile efavirenz AUC in non-pregnant historical controls (40.0 mcg.hr/mL) and a trough concentration of 1 mcg/mL.
Results
Twenty five women were enrolled during the third trimester: median (range) age was 29.3 (18.9–42.9) years, weight 69.0 (40–130) kg, gestational age 32.9 (30.1–38.7) weeks. Median (range) efavirenz AUC0-24, Cmax and C24hour were 55.4 mcg.hr/mL (13.5–220.3), 5.4 mcg/mL (1.9–12.2) and 1.6 mcg/ml (0.23–8.13), respectively. Efavirenz AUC and Cmax did not differ during pregnancy and postpartum but C24hour was lower during the third trimester (1.6 vs. 2.1 mcg/mL, p=0.01). During the third trimester, 5 of 25 (20%) women had an efavirenz AUC below the target and 3 of 25 (12%) had a trough concentration below 1 mcg/mL. Efavirenz cord blood/maternal concentration ratio was 0.49 (0.37–0.74). All women had a HIV-1 RNA viral load less than 400 copies/mL at delivery and 19 (76%) had a viral load below 50 copies/mL. One child was perinatally HIV-infected. Three women were exposed to efavirenz throughout the first 6 weeks of pregnancy. EFV was well tolerated and among the 25 infants no congenital anomalies or newborn complications were reported.
Conclusions
Changes in efavirenz pharmacokinetics during pregnancy compared to postpartum are not sufficiently large enough to warrant a dose adjustment during pregnancy.
doi:10.1097/QAI.0b013e31823ff052
PMCID: PMC3288559  PMID: 22083071
efavirenz; pregnancy; pharmacokinetics; HIV; prevention of mother-to-child transmission of HIV
6.  Use of Pharmacokinetic and Pharmacodynamic Principles To Determine Optimal Administration of Daptomycin in Patients Receiving Standardized Thrice-Weekly Hemodialysis▿  
This study identified optimal daptomycin dosing for patients receiving thrice-weekly hemodialysis (HD). Twelve adult patients on HD received daptomycin at 6 mg/kg of body weight intravenously (i.v.) one time; plasma and dialysate samples were collected over 3 days. A 2-compartment model with separate HD and non-HD clearance terms was fit to the data. A series of 9,999-subject Monte Carlo simulations (MCS) was performed to identify HD dosing schemes providing efficacy and toxicity profiles comparable to those obtained for MCS employing the daptomycin population pharmacokinetic (PK) model derived from patients in the Staphylococcus aureus bacteremia-infective endocarditis (SAB-IE) study. For efficacy, we selected the HD dosing scheme which generated an area-under-the-curve (AUC) exposure profile comparable to that for the SAB-IE population model. For toxicity, we selected HD dosing schemes that minimized trough concentrations of ≥24.3 mg/liter. Separate HD dosing schemes were developed for each FDA-approved regimen and for two weekly interdialytic periods (48 and 72 h). Administration of the same parent daptomycin dose intra-HD and post-HD resulted in AUC, maximum concentration of drug in serum (Cmax), and Cmin values most comparable to those for SAB-IE simulations for the 48-hour interdialytic period. In contrast, all candidate HD dosing schemes provided AUC48-72 values that were at least 50% lower than the SAB-IE AUC48-72 values. Increasing the parent dose by 50% provided more comparable AUC48-72 values while maintaining acceptable Cmin values. Administration of the daptomycin parent dose intra-HD or post-HD was optimal for the 48-h interdialytic period. For the 72-h interdialytic period, clinicians should consider increasing the dose by 50% to achieve more comparable AUC48-72 values.
doi:10.1128/AAC.01224-10
PMCID: PMC3067175  PMID: 21282429
7.  Comparative efficacy of daptomycin, vancomycin, and cloxacillin for the treatment of Staphylococcus aureus endocarditis in rats and role of test conditions in this determination. 
Antimicrobial Agents and Chemotherapy  1990;34(12):2348-2353.
The in vivo efficacy of daptomycin, a new cell wall-active anti-gram-positive-bacterial agent, was compared to those of cloxacillin and vancomycin in a rat model of Staphylococcus aureus endocarditis. Both methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains were used. When therapy was initiated early (8 h) after infection, at the time when valvular bacterial counts were relatively low (approximately 10(6) CFU/g of vegetation), 3 days of therapy was found to be effective against the MSSA strains whatever the antibiotic regimen. In contrast, when the onset of therapy was delayed up to 15 h after infection, so that higher bacterial counts could develop on the valves (approximately 10(9) CFU/g of vegetation), a longer period of treatment (6 days) was required to cure infection. Under these conditions after 3 days of therapy, daptomycin was more effective than cloxacillin and vancomycin against the MSSA strains. Similarly, daptomycin showed a greater activity than vancomycin against the MRSA strain after 3 days of treatment, but after 6 days both antibiotics were equally effective. Decreasing doses of daptomycin showed decreasing activity: 10 mg/kg of body weight every 12 h (q12h) was better than 5 mg/kg q12h, whereas 5 mg/kg q24h (providing drug levels in blood detectable only during the first 12 h) failed to cure infection. In vitro, daptomycin was highly bactericidal at high concentrations (25 and 60 micrograms/ml, corresponding to peak levels in serum after doses of 5 and 10 mg/kg, respectively) and bacteriostatic at lower concentrations (0.5 to 2.5 micrograms/ml, corresponding to trough levels in serum). In conclusion, against low-bacterial-count S. aureus endocarditis, daptomycin showed an efficacy similar to those of vancomycin and cloxacillin. Against high-bacterial-count S. aureus endocarditis, daptomycin showed a higher bactericidal activity than cloxacillin (against the MSSA strains) and vancomycin (against both the MSSA and MRSA strains).
PMCID: PMC172059  PMID: 1965105
8.  Efficacy of Daptomycin-Cloxacillin Combination in Experimental Foreign-Body Infection Due to Methicillin-Resistant Staphylococcus aureus 
Despite the use of daptomycin alone at high doses (greater than 6 mg/kg of body weight/day) against difficult-to-treat infections, clinical failures and resistance appeared. Recently, the combination daptomycin-cloxacillin showed enhanced efficacy in clearing bacteremia caused by methicillin-resistant Staphylococcus aureus (MRSA). The aim of this study was to evaluate the efficacy of daptomycin at usual and high doses (equivalent to 6 and 10 mg/kg/day in humans, respectively) in combination with cloxacillin in a rat tissue cage infection model by MRSA and to compare its efficacy to that of daptomycin-rifampin. We used MRSA strain ATCC BAA-39. In the log- and stationary-phase kill curves, daptomycin-cloxacillin improved the bactericidal activity of daptomycin, especially in log phase. For in vivo studies, therapy was administered intraperitoneally for 7 days with daptomycin at 100 mg/kg/day and 45/mg/kg/day (daptomycin 100 and daptomycin 45), daptomycin 100-cloxacillin at 200 mg/kg/12 h, daptomycin 45-cloxacillin, and daptomycin 100-rifampin at 25 mg/kg/12 h. Daptomycin-rifampin was the best therapy (P < 0.05). Daptomycin 45 was the least effective treatment and did not protect against the emergence of resistant strains. There were no differences between the two dosages of daptomycin plus cloxacillin in any situation, and both protected against resistance. The overall effect of the addition of cloxacillin to daptomycin was a significantly greater cure rate (against adhered bacteria) than that for daptomycin alone. In conclusion, daptomycin-cloxacillin enhanced modestly the in vivo efficacy of daptomycin alone against foreign-body infection by MRSA and was less effective than daptomycin plus rifampin. The benefits of adding cloxacillin to daptomycin should be especially evaluated against infections by rifampin-resistant MRSA and for protection against the emergence of daptomycin nonsusceptibility.
doi:10.1128/AAC.00127-12
PMCID: PMC3393403  PMID: 22585211
9.  The Effect of Age and Weight on Vancomycin Serum Trough Concentrations in Pediatric Patients 
Pharmacotherapy  2013;33(12):10.1002/phar.1331.
Background
Vancomycin treatment failure has been associated with low serum vancomycin trough concentrations, prompting recommendations to increase the daily doses in adults and children. Despite more aggressive vancomycin dosing, there continues to be significant variability in vancomycin trough concentrations in pediatric patients.
Methods
To determine if vancomycin trough concentrations in pediatric patients differ by age and weight, we reviewed records of hospitalized patients who received vancomycin between 2008 and 2012. Patients were divided into groups that received vancomycin 40 mg/kg/day (2008 to 2009) or 60 mg/kg/day (2010 to 2012). Vancomycin trough concentrations were compared between groups and within the 60-mg/kg/day group, stratified by patient age and weight.
Results
After increasing the vancomycin dose from 40 mg/kg/day to 60 mg/kg/day, initial trough concentrations increased significantly in patients younger than 2 and greater than 6 years of age, but not in patients between the ages of 2 and 5 years. In the 60-mg/kg/day group, only 16.7% of patients between 2 and 5 years of age had initial trough concentrations in the therapeutic range (10 mcg/mL to 20 mcg/mL). Initial trough concentrations were therapeutic in a greater proportion of patients ages 6 years to 12 years (38.7%) and 13 years to 18 years (63.0%). Patients between the ages of 13 and 18 had the highest proportion of supratherapeutic initial vancomycin trough concentrations (14.8%). Patients weighing > 50 kg had significantly higher trough concentrations than patients ≤ 50 kg (17.1 mcg/mL vs. 9.3 mcg/mL; p<0.001).
Conclusion
Although increasing the vancomycin dose from 40 mg/kg/day to 60 mg/kg/day led to a significant increase in vancomycin trough concentrations, a large proportion of patients receiving 60 mg/kg/day of vancomycin had trough concentrations outside of the therapeutic range. Specifically, patients younger than 6 years tend to have low trough concentrations, while adolescents and children > 50 kg are more likely to have elevated trough concentrations. Vancomycin dosing strategies in pediatric patients should consider age and weight as well as renal function and indication.
doi:10.1002/phar.1331
PMCID: PMC3842376  PMID: 23864541
vancomycin; pediatric; weight; age
10.  Mycophenolate Pharmacokinetics and Association with Response to Acute Graft vs Host Disease (GVHD) Treatment From the Blood and Marrow Transplant Clinical Trials Network 
There are limited data as to the effectiveness of MMF plus high dose corticosteroids for the treatment of acute GVHD and even less data regarding the pharmacokinetic disposition and exposure-response relationship of mycophenolate in individuals with GVHD. Mycophenolate pharmacokinetics were studied in a multi-center CTN randomized phase II trial evaluating the effectiveness of MMF as one of four agents added to corticosteroids as treatment of acute GVHD. Thirty-two of the patients randomized to receive MMF underwent pharmacokinetic sampling in weeks 1 and 2 were studied. Mean±sd age was 41±13.6 years. Twenty one (65.6%), 5 (15.6%), 6 (18.8%) patients had a complete response (CR), partial response (PR) or lesser response by day 28, respectively. Twenty-five (78.1%), 2 (6.3%), 5 (15.6%) patients had a CR, PR, or other response by day 56 to treatment, respectively. Single mycophenolic acid (MPA) pharmacokinetic measurements from weeks 1 and 2 did not correlate with CR at either day 28 or 56 (p>0.07). However, if the mean of weeks 1 and 2 total MPA troughs was >0.5 mcg/mL or unbound trough >0.015 mcg/mL, a significantly greater proportion achieved a CR+PR at day 28 and 56. A CR+PR at day 28 was observed in 19/19 (100%) of patients if the mean total trough was >0.5 mg/mL, but in only 7/13 (54%) if ≤0.5 mcg/mL (p=0.002). Similarly, 15/15 (100%) individuals had a CR+PR at day 28 if their unbound MPA trough concentration was >0.015 mcg/mL while only 11/17 (65%) responded if trough was ≤0.015 mcg/mL (p=0.02). There was no association between the pharmacokinetic measures and risk of infection by day 90 or overall survival at day 180 post randomization. About one-half of subjects’ therapy did not achieve the favorable MPA total and unbound trough concentrations. The current practice of MMF 1 gm twice daily dosing provides low plasma concentrations in many patients. Increased dosing at 3 gm/day may improve the efficacy of MMF as acute GVHD therapy.
doi:10.1016/j.bbmt.2009.11.010
PMCID: PMC3104501  PMID: 19925875
11.  In vitro pharmacodynamic effects of concentration, pH, and growth phase on serum bactericidal activities of daptomycin and vancomycin. 
Antimicrobial Agents and Chemotherapy  1992;36(12):2709-2714.
Clinical trials with daptomycin were halted in December 1990 because of treatment failures including two resistant Staphylococcus aureus strains. High protein binding of daptomycin (> 90%) and the lower-than-expected concentrations in serum with the dosage regimen of 3 mg/kg of body weight every 12 h may have contributed to these failures. To evaluate the effect that higher concentrations would have on bactericidal activity measured by time-kill curves, peak and trough concentrations were estimated for dosage regimens of 3, 5, and 10 mg/kg every 12 h. MICs, MBCs, and killing curves for daptomycin and vancomycin were performed by using the estimated concentrations with four S. aureus strains obtained from patients who failed daptomycin therapy for endocarditis. MICs and MBCs of daptomycin demonstrated a greater inoculum effect than those of vancomycin; MICs and MBCs of daptomycin increased three- to fourfold, but those of vancomycin increased only one- to twofold when the inoculum was increased from 5 x 10(5) to 5 x 10(7) CFU/ml. No pH-dependent effect on MICs or MBCs was seen. Strenuous experimental conditions were chosen: high inoculums (5 x 10(7) CFU/ml), extremes of pH (6.4, 7.4, and 8), and stationary and exponentially growing organisms; and all experiments completed in the presence of pooled human serum. Daptomycin exhibited concentration-dependent killing and statistically faster kill rates than vancomycin against stationary- or exponential-growth-phase organisms. A pH-dependent decrease in activity with daptomycin was also demonstrated. Daptomycin and vancomycin produced higher kill rates against exponentially growing organisms. A pH-dependent decrease in activity with daptomycin was also demonstrated. Daptomycin and vancomycin produced higher kill rates against exponentially growing organisms. The results indicate that the use of higher dosage regimens with compounds similar to daptomycin may be capable of overcoming the effects of pH, high inoculum, and protein binding.
PMCID: PMC245533  PMID: 1336344
12.  Empiric guideline-recommended weight-based vancomycin dosing and nephrotoxicity rates in patients with methicillin-resistant Staphylococcus aureus bacteremia: a retrospective cohort study 
Background
Previous studies have established a correlation between vancomycin troughs and nephrotoxicity. However, data are currently lacking regarding the effect of guideline-recommended weight-based dosing on nephrotoxicity in methicillin-resistant Staphylococcus aureus bacteremia (MRSAB).
Methods
Adults who were at least 18 years of age with methicillin-resistant Staphylococcus aureus bacteremia and received of empiric vancomycin therapy for at least 48 hours (01/07/2002 and 30/06/2008) were included in this multicenter, retrospective cohort study. The association between guideline-recommended, weight-based vancomycin dosing (at least 15 mg/kg/dose) and nephrotoxicity (increase in serum creatinine (SCr) by more than 0.5 mg/dl or at least a 50% increase from baseline on at least two consecutive laboratory tests) was evaluated. Potential independent associations were evaluated using a multivariable general linear mixed-effect model.
Results
Overall, 23% of patients developed nephrotoxicity. Thirty-four percent of the 337 patients who met study criteria received weight-based dosing. The cohort was composed of 69% males with a median age of 55 years. The most common sources of MRSAB included skin/soft tissue (32%), catheter-related bloodstream bacteremia (20%), pulmonary (18%). Eighty-six percent of patients received twice daily dosing. Similar rates of nephrotoxicity were observed regardless of the receipt of guideline-recommended dosing (22% vs. 24%, OR 0.91 [95% CI 0.53-1.56]). This finding was confirmed in the multivariable analysis (OR 1.52 [95% CI 0.75-3.08]). Independent predictors of nephrotoxicity were (OR, 95% CI) vancomycin duration of greater than 15 days (3.36, 1.79-6.34), weight over 100 kg (2.74, 1.27-5.91), Pitt bacteremia score of 4 or greater (2.73, 1.29-5.79), vancomycin trough higher than 20 mcg/ml (2.36, 1.07-5.20), and age over 52 years (2.10, 1.08-4.08).
Conclusions
Over one out of five patients in this study developed nephrotoxicity while receiving vancomycin for MRSAB. The receipt of guideline-recommended, weight-based vancomycin was not an independent risk factor for the development of nephrotoxicity.
doi:10.1186/2050-6511-14-12
PMCID: PMC3575285  PMID: 23402420
Adverse events; Nephrotoxicity; Vancomycin; Dosing; Weight; Obesity; MRSA
13.  Pharmacokinetics of an Increased Atazanavir Dose with and without Tenofovir During the Third Trimester of Pregnancy 
Background
Reduced atazanavir exposure has been demonstrated during pregnancy with standard atazanavir/ritonavir dosing. We studied an increased dose during the third trimester of pregnancy.
Methods
IMPAACT 1026s is a prospective, non-blinded pharmacokinetic study of HIV-infected pregnant women taking antiretrovirals for clinical indications, including two cohorts (with or without tenofovir) receiving atazanavir/ritonavir 300/100 mg once daily during the 2nd trimester (2nd trim), 400/100 mg during the 3rd trimester (3rd trim) and 300/100 mg postpartum (PP). Intensive steady-state 24-hour pharmacokinetic profiles were performed. Atazanavir concentrations were measured by HPLC. Pharmacokinetic targets were the 10th percentile atazanavir AUC (29.4 mcg*hr/mL) in non-pregnant adults on standard dose and 0.15 mcg/mL, minimum trough concentration.
Results
Atazanavir pharmacokinetic data were available for 37 women without tenofovir, 35 with tenofovir; Median (range) pharmacokinetic parameters are presented for 2nd, 3rd trim and PP and number who met target/total. * indicates p<0.05 compared to PP.
Atazanavir without tenofovir
AUC 30.5 (9.19–93.8), 45.7 (11–88.3), and 48.8 (9.9–112.2) mcg-hr/mL, and 8/14, 29/37 and 27/34 met target. C24h was 0.49 (0.09–4.09), 0.71 (0.14–2.09), and 0.90 (0.05–2.73) mcg/mL; 13/14, 36/37 and 29/34 met target.
Atazanavir with tenofovir
AUC 26.2 (6.8–60.9)*, 37.7 (0.72–88.2)*, and 58.6 (6–149) mcg-hr/mL, and 7/17, 23/32 and 27/29 met target. C24h was 0.44 (0.12–1.06)*, 0.57 (0.02–2.06)*, and 1.26 (0.09–5.43) mcg/mL; 7/17, 23/32 and 27/29 met target. Atazanavir/ritonavir was well tolerated with no unanticipated adverse events.
Conclusions
Atazanavir/ritonavir increased to 400/100mg provides adequate atazanavir exposure during the third trimester and should be considered during the second trimester.
doi:10.1097/QAI.0b013e318289b4d2
PMCID: PMC3625451  PMID: 23392467
atazanavir; tenofovir; pharmacokinetics; pregnancy; HIV; mother to child transmission
14.  Differential increased survival of staphylococci and limited ultrastructural changes in the core of infected fibrin clots after daptomycin administration. 
A possible explanation for the difficulties encountered in curing deep fibrin-embedded infections is that antibiotic diffusion inside the infected fibrin matrix is not homogeneous and is insufficient to neutralize the pathogen. To evaluate this conjecture, the differential pharmacodynamics of daptomycin in fibrin clots infected with methicillin-susceptible and -resistant Staphylococcus aureus and Staphylococcus epidermidis was estimated. Daptomycin (20 or 50 mg/kg of body weight) was infused over 30 min. Fibrin clots and blood samples were evaluated from 0.5 to 42 h after the injections. The half-lives of daptomycin in serum and fibrin clot were close to identical after the two doses and averaged 5.4 and 22 h, respectively. The mean areas under the concentration-time curves from 0 to 42 h (AUC0-infinity) for daptomycin concentrations in serum and infected clots were 575 +/- 36.7 and 215 +/- 6.2 micrograms/g/h after administration of 20 mg/kg and 1,089 +/- 39.9 and 326 +/- 16.8 micrograms/g/h after administration of 50 mg/kg. A concentration gradient from the periphery to the core of the clots was observed in many clots up to 18 h after treatment. Mean peak concentrations in the core of the clots reached 60% of the peripheral values (P < 0.05) and were delayed for at least 3 h compared with the peripheral peak concentrations. AUC0-42 h of daptomycin concentration in the periphery and the core of clots were significantly different (P < 0.01). Survival of microorganisms was better in the core than in the periphery, with as much as a 3 log10 CFU/g difference between the center and the surface of the clot. Bacterial examination by transmission electron microscopy also showed noticeable differences in ultrastructural changes between those in the periphery and those in the core of the clots. In conclusion, the pharmacokinetics of daptomycin are significantly different at the periphery and within the core of fibrin clots, which may have led to the higher bacterial survival in the core of clots. Limited diffusion of daptomycin in fibrin, an essential component of the vegetation in bacterial endocarditis, could explain at least in part some of the treatment failures.
PMCID: PMC163083  PMID: 8787906
15.  In Vivo Pharmacodynamic Activity of Daptomycin 
Daptomycin is a lipopeptide antibiotic with activity against a wide range of gram-positive bacteria. We used the neutropenic murine thigh model to characterize the pharmacodynamics of daptomycin. ICR/Swiss mice were rendered neutropenic with cyclophosphamide; and the thigh muscles of the mice were infected with strains of Staphylococcus aureus, Streptococcus pneumoniae, and Enterococcus faecium. Animals were treated by subcutaneous injection of daptomycin at doses of 0.20 to 400 mg/kg of body weight/day divided into one, two, four, or eight doses over 24 h. Daptomycin exhibited linear pharmacokinetics, with an area under the concentration-time curve (AUC) from time zero to infinity/dose of 9.4 and a half-life of 0.9 to 1.4 h. The level of protein binding was 90%. Free daptomycin exhibited concentration-dependent killing and produced in vivo postantibiotic effects (PAEs) of 4.8 to 10.8 h. Nonlinear regression analysis was used to determine which pharmacokinetic (PK) or pharmacodynamic (PD) parameter was important for efficacy by using free drug concentrations. The peak concentration/MIC (peak/MIC) ratio and 24-h AUC/MIC ratio were the PK and PD parameters that best correlated with in vivo efficacy (R2 = 83 to 87% for peak/MIC and R2 = 86% for the AUC/MIC ratio, whereas R2 = 47 to 50% for the time that the concentration was greater than the MIC) against standard strains of S. aureus and S. pneumoniae. The peak/MIC ratios required for a bacteriostatic effect ranged from 12 to 36 for S. pneumoniae, 59 to 94 for S. aureus, and 0.14 to 0.25 for E. faecium. The AUC/MIC ratios needed for a bacteriostatic effect ranged from 75 to 237 for S. pneumoniae, 388 to 537 for S. aureus, and 0.94 to 1.67 for E. faecium. The free daptomycin concentrations needed to average from one to two times the MIC over 24 h to produce a bacteriostatic effect and two to four times the MIC over 24 h to produce greater than 99% killing. The long PAE and potent bactericidal activity make daptomycin an attractive option for the treatment of infections caused by gram-positive bacteria.
doi:10.1128/AAC.48.1.63-68.2004
PMCID: PMC310158  PMID: 14693519
16.  Prospective, Open-Label Investigation of the Pharmacokinetics of Daptomycin during Cardiopulmonary Bypass Surgery▿ 
As methicillin-resistant Staphylococcus aureus (MRSA) becomes more prevalent, vancomycin is becoming increasingly used as a prophylaxis against surgical-site infections for cardiothoracic surgeries. However, vancomycin administration can be challenging, and the pharmacokinetics of alternative antibiotics in this setting are poorly understood. The primary objective of this investigation was to describe the pharmacokinetics of daptomycin in patients undergoing coronary artery bypass graft surgery. We enrolled 15 patients undergoing coronary artery bypass surgery requiring cardiopulmonary bypass. Each subject was administered a single open-label dose of daptomycin (8 mg/kg of body weight) for surgical prophylaxis. Fourteen daptomycin plasma samples were collected. Safety outcomes between subjects who received daptomycin and 15 control subjects who received the standard-of-care antibiotic were compared. The mean maximal concentration of daptomycin (Cmax) was 84.4 ± 27.1 μg/ml; the mean daptomycin concentration during the cardiopulmonary bypass procedure was 33.2 ± 11.4 μg/ml and was 30.9 ± 12.7 μg/ml at sternum closure. Mean daptomycin concentrations at 12, 18, 24, and 48 h were 22.7 ± 9.7, 16.2 ± 8.2, 12.0 ± 4.7, and 3.5 ± 2.3 μg/ml, respectively. Mean daptomycin concentrations were consistently above the MIC at which 90% of the tested isolates are inhibited (MIC90) for S. aureus and S. epidermidis during the cardiopulmonary bypass procedure. Daptomycin was not associated with surgical-site infections or differences in adverse events compared to findings for control subjects. We found that a single dose of daptomycin at 8 mg/kg was well tolerated and achieved adequate plasma concentrations against common pathogens associated with surgical-site infections after cardiothoracic surgery. Daptomycin may be considered an alternative surgical prophylaxis antibiotic for patients undergoing cardiothoracic bypass surgery who are unable to receive vancomycin.
doi:10.1128/AAC.01404-10
PMCID: PMC3101392  PMID: 21444695
17.  Daptomycin Pharmacokinetics and Safety following Administration of Escalating Doses Once Daily to Healthy Subjects 
The purpose of this paper is to establish the pharmacokinetics and safety of escalating, once-daily doses of daptomycin, a novel lipopeptide antibiotic active against gram-positive pathogens, including those resistant to methicillin and vancomycin. This phase 1, multiple-dose, double-blind study involved 24 healthy subjects in three dose cohorts (4, 6, and 8 mg/kg of body weight) who were randomized to receive daptomycin or the control at a 3:1 ratio and administered the study medication by a 30-min intravenous infusion every 24 h for 7 to 14 days. Daptomycin pharmacokinetics was assessed by blood and urine sampling. Safety and tolerability were evaluated by monitoring adverse events (AEs) and laboratory parameters. Daptomycin pharmacokinetics was linear through 6 mg/kg, with a slight (∼20%) nonlinearity in the area under the curve and trough concentration at the highest dose studied (8 mg/kg). The pharmacokinetic parameters measured on the median day of the study period, (day 7) were half-life (∼9 h), volume of distribution (∼0.1 liters/kg), systemic clearance (∼8.2 ml/h/kg), and percentage of the drug excreted intact in urine from 0 to 24 h (∼54%). Daptomycin protein binding (mean amount bound, 91.7%) was independent of the drug concentration. No gender effect was observed. All subjects who received daptomycin completed the study. The frequencies and distributions of treatment-emergent AEs were similar for the subjects who received daptomycin and the control subjects. There were no serious AEs and no pattern of dose-related events. The pharmacokinetics of once-daily administration of daptomycin was linear through 6 mg/kg. For all three doses, plasma daptomycin concentrations were consistent and predictable throughout the dosing interval. Daptomycin was well tolerated when it was administered once daily at a dose as high as 8 mg/kg for 14 days.
doi:10.1128/AAC.47.4.1318-1323.2003
PMCID: PMC152488  PMID: 12654665
18.  PHASE 1 STUDY OF VALPROIC ACID IN PEDIATRIC PATIENTS WITH REFRACTORY SOLID OR CNS TUMORS: A CHILDREN’S ONCOLOGY GROUP REPORT 
Purpose
The primary purpose of this trial was to define and describe the toxicities of oral valproic acid (VPA) at doses required to maintain trough concentrations of 100–150 mcg/ml or 150–200 mcg/ml in children with refractory solid or CNS tumors. Secondary objectives included assessment of free and total VPA pharmacokinetics and histone acetylation in peripheral blood mononuclear cells (PBMC) at steady state.
Patients and Methods
Oral VPA, initially administered twice daily and subsequently three times daily, was continued without interruption to maintain trough concentrations of 100–150 mcg/ml. First-dose and steady state pharmacokinetics were studied. Histone H3 and H4 acetylation in PBMCs was evaluated using an ELISA technique.
Results
Twenty six children, 16 of whom were evaluable for toxicity, were enrolled. Dose-limiting somnolence and intra-tumoral hemorrhage were associated with VPA troughs of 100–150 mcg/ml. Therefore, the final cohort of six children received VPA to maintain troughs of 75–100 mcg/ml and did not experience any dose-limiting toxicity. First-dose and steady state VPA pharmacokinetic parameters were similar to values previously reported in children with seizures. Increased PBMC histone acetylation was documented in 50% of patients studied. One confirmed partial response (glioblastoma multiforme) and one minor response (brainstem glioma) were observed.
Conclusions
VPA administered three times daily to maintain trough concentrations of 75–100 mcg/ml was well tolerated in children with refractory solid or CNS tumors. Histone hyper-acetylation in PBMCs was observed in half of the patients at steady state. Future trials combining VPA with chemotherapy and/or radiation therapy should be considered, especially for CNS tumors.
doi:10.1158/1078-0432.CCR-10-0738
PMCID: PMC3064523  PMID: 21115653
Valproic acid; Histone deacetylase inhibitor; CNS tumors; Pediatric phase I study; Solid tumors
19.  Pharmacokinetically Guided Phase 1 Trial of the IGF-1 Receptor Antagonist RG1507 in Children with Recurrent or Refractory Solid Tumors 
Purpose
This pediatric phase I study was designed to identify the doses of RG1507, a monoclonal antibody against the Type 1 Insulin-like Growth Factor Receptor (IGF1R), that achieve exposures equivalent to those achieved in adults at recommended doses.
Experimental Design
Children with relapsed or refractory solid tumors were treated using the same doses and administration schedules of RG1507 [3 and 9mg/kg/week, and 16 mg/kg every 3 weeks (q3W)] as those studied in adults. Detailed pharmacokinetic (PK) sampling was performed after the 1st dose; selected peak and trough levels were subsequently obtained. Target exposures were •85% of mean areas under concentration x time curves (AUCs) in adults at doses of 9 mg/kg/week and 16 mg/kg q3W. A maximum tolerated dose could be identified if dose-limiting toxicities (DLT) occurred.
Results
Thirty-one evaluable patients ages 3–17 years were enrolled at 3 mg/kg/week (n=3), 9 mg/kg/week (n=18), or 16 mg/kg q3W (n=10). There were no DLTs. At 9 mg/kg/wk the mean AUC0–7d (21,000 mcg•h/mL) exceeded the target (16,000 mcg•h/mL). At 16 mg/kg q3W, the mean AUC0–21d (70,000 mcg•h/mL) exceeded the target (59,400 mcg•h/mL). Clearance normalized to body weight was age dependent. There were no objective responses. Seven patients had stable disease for >12 weeks, including two patients with osteosarcoma with stable disease for 52+ and 78+ weeks.
Conclusions
The recommended doses of RG1507 in children with solid tumors are 9 mg/kg/week and 16 mg/kg q3W. This flexible design is well-suited for trials of agents associated with limited toxicity.
doi:10.1158/1078-0432.CCR-10-1731
PMCID: PMC4283561  PMID: 21127194
20.  Assessment of effects of protein binding on daptomycin and vancomycin killing of Staphylococcus aureus by using an in vitro pharmacodynamic model. 
Antimicrobial Agents and Chemotherapy  1990;34(10):1925-1931.
Initial clinical trials with daptomycin (2 mg/kg per day) were prematurely suspended because of unexplained treatment failures in patients with bacteremia who were treated with daptomycin, despite in vitro data indicating that the gram-positive cocci causing the infection were susceptible to daptomycin. One explanation for these clinical failures may relate to the relatively high degree of daptomycin protein binding (94%). To evaluate the impact of protein on daptomycin activity, a two-chamber in vitro pharmacodynamic model was used to study and compare the interaction between Staphylococcus aureus (clinical isolate) and either daptomycin or vancomycin, each in the presence and absence of physiologic human albumin concentrations. Low-dose (2 mg/kg) daptomycin, high-dose (6 mg/kg) daptomycin, and 10 mg of vancomycin per kg beta-phase elimination serum-concentration-versus-time curves were simulated by using this in vitro pharmacodynamic model. The bacterial kill rates by all three regimens were decreased in the presence of albumin (P less than 0.0002). The average times required for a 99% kill of the initial S. aureus inocula (approximately 5 x 10(7) CFU/ml) without albumin were 0.81 (low-dose daptomycin), 0.33 (high-dose daptomycin), and 6.18 (vancomycin) h. The average times required for a 99% kill of S. aureus with albumin were 7.66 (low-dose daptomycin), 0.95 (high-dose daptomycin), and 10.52 (vancomycin) h. These data demonstrate that, depending on the concentration of daptomycin, the presence of albumin can profoundly diminish the bactericidal activity of daptomycin.
PMCID: PMC171966  PMID: 1963288
21.  Safety and efficacy of high-dose daptomycin as salvage therapy for severe gram-positive bacterial sepsis in hospitalized adult patients 
Background
Increasing the dosage of daptomycin may be advantageous in severe infection by enhancing bactericidal activity and pharmacodynamics. However, clinical data on using daptomycin at doses above 6 mg/kg in Asian population are limited.
Methods
A retrospective observational cohort study of all hospitalized adult patients treated with daptomycin (> 6 mg/kg) for at least 72 hours was performed in Taiwan.
Results
A total of 67 patients (40 males) with a median age of 57 years received a median dose of 7.61 mg/kg (range, 6.03-11.53 mg/kg) of daptomycin for a median duration of 14 days (range, 3–53 days). Forty-one patients (61.2%) were in intensive care units (ICU). Sites of infections included complicated skin and soft tissue infections (n = 16), catheter-related bacteremia (n = 16), endocarditis (n = 11), primary bacteremia (n = 10), osteomyelitis and septic arthritis (n = 9), and miscellaneous (n = 5). The median Pitt bacteremia score among the 54 (80.6%) patients with bacteremia was 4. The most common pathogen was methicillin-resistant Staphylococcus aureus (n = 38). Fifty-nine patients (88.1%) were treated with daptomycin after glycopepetide use. Overall, 52 (77.6%) patients achieved clinical success. The all-cause mortality rate at 28 day was 35.8%. In multivariate analysis, the significant predictors of in-hospital mortality in 54 bacteremic patients were malignancies (P = 0.01) and ICU stay (P = 0.02). Adverse effects of daptomycin were generally well-tolerated, leading to discontinuation in 3 patients. Daptomycin-related creatine phosphokinase (CPK) elevations were observed in 4 patients, and all received doses > 8 mg/kg.
Conclusions
Treatment with high dose daptomycin as salvage therapy was generally effective and safe in Taiwan. CPK level elevations were more frequent in patients with dose > 8 mg/kg.
doi:10.1186/1471-2334-13-66
PMCID: PMC3571896  PMID: 23379510
Daptomycin; High dose; Creatine phosphokinase; Treatment outcomes
22.  Reduction in magnetic resonance imaging T2 burden of disease in patients with relapsing-remitting multiple sclerosis: analysis of 48-week data from the EVIDENCE (EVidence of Interferon Dose-response: European North American Comparative Efficacy) study 
BMC Neurology  2008;8:11.
Background
The EVIDENCE (EVidence of Interferon Dose-response: European North American Comparative Efficacy) study was an international, randomized, open-label, assessor-blinded, parallel-group study assessing the efficacy and tolerability of interferon (IFN) beta-1a, 44 mcg subcutaneously (sc) three times weekly (tiw), and IFN beta-1a, 30 mcg intramuscularly (im) once weekly (qw), in patients with relapsing-remitting multiple sclerosis (RRMS). The aim of this analysis was to assess whether reductions in T2 burden of disease (BOD) were greater for patients receiving IFN beta-1a, 44 mcg sc tiw, than for those treated with IFN beta-1a, 30 mcg im qw, and to assess the impact of neutralizing antibodies (NAbs).
Methods
A post-hoc analysis was performed on magnetic resonance imaging (MRI) data collected prospectively from the EVIDENCE study. The analysis included all patients with evaluable T2 MRI scans at the start of dosing and at week 48, and those who received at least one drug dose (n = 553). Lesions were identified by a radiologist blinded to treatment codes and the total volume of T2 lesions (BOD) was reported in mm3.
Results
Both median percentage decreases and absolute reduction in BOD were greater in the IFN beta-1a, 44 mcg sc tiw, treatment group. The adjusted mean treatment difference in percentage change in BOD from baseline to week 48 showed a significant treatment benefit for patients treated with IFN beta-1a, 44 mcg sc tiw, over those treated with IFN beta-1a, 30 mcg im qw (-4.6%; standard error: 2.6%; p = 0.002). The presence of NAbs reduced the effect of IFN beta-1a 44, mcg sc tiw, on BOD, but BOD changes were still similar to those seen with IFN beta-1a, 30 mcg im qw.
Conclusion
Patients with RRMS treated with IFN beta-1a, 44 mcg sc tiw, had greater reduction in T2 BOD after 48 weeks than those treated with IFN beta-1a, 30 mcg im qw, which is consistent with other clinical and MRI outcome measures in the EVIDENCE study. In patients testing positive for NAbs (NAb+) to IFN beta-1a 44 mcg sc tiw, changes in BOD were smaller than in NAb negative (NAb-) patients, but similar to those receiving IFN beta-1a, 30 mcg im qw.
doi:10.1186/1471-2377-8-11
PMCID: PMC2374794  PMID: 18426595
23.  Pharmacokinetics of Intravenous Voriconazole in Obese Patients: Implications of CYP2C19 Homozygous Poor Metabolizer Genotype 
Pharmacotherapy  2013;33(3):e19-e22.
There is a paucity of pharmacokinetic studies describing weight-based dosing of intravenous (IV) voriconazole in obesity. We report the pharmacokinetics of IV voriconazole in an obese CYP2C19 homozygous poor metabolizer and review previously reported data of IV voriconazole in obesity. A 17-year-old obese Hispanic male (BMI=35 kg/m2) received IV voriconazole for treatment of suspected aspergillosis. After 2.5 days of voriconazole 4 mg/kg IV every 12 hours using adjusted body weight, the voriconazole area under the serum concentration versus time curve over the course of a single dosing interval (AUC0–12) and trough concentration were 86,100 ng•h/ml and 6.2 mcg/ml, respectively. The voriconazole dosage was then decreased. A trough concentration drawn just before dose reduction (after 8.5 days of voriconazole 4 mg/kg IV every 12 hours) remained elevated (5.8 mcg/ml). Genotyping revealed a CYP2C19 homozygous poor metabolizer (CYP2C19*2/*2). Voriconazole was subsequently discontinued due to QTc prolongation. These data and two recent publications suggest that voriconazole does not distribute extensively into human adipose tissue and that obese patients should be dosed on an adjusted weight basis. If an obese patient dosed on total body weight is also a CYP2C19 poor metabolizer, serum voriconazole concentrations will be further elevated, potentially leading to drug-induced toxicity.
doi:10.1002/phar.1192
PMCID: PMC3594083  PMID: 23400848
voriconazole; obese; intravenous; CYP2C19; pharmacokinetics
24.  Efficacy of Daptomycin in Implant-Associated Infection Due to Methicillin-Resistant Staphylococcus aureus: Importance of Combination with Rifampin▿  
Limited treatment options are available for implant-associated infections caused by methicillin (meticillin)-resistant Staphylococcus aureus (MRSA). We compared the activity of daptomycin (alone and with rifampin [rifampicin]) with the activities of other antimicrobial regimens against MRSA ATCC 43300 in the guinea pig foreign-body infection model. The daptomycin MIC and the minimum bactericidal concentration in logarithmic phase and stationary growth phase of MRSA were 0.625, 0.625, and 20 μg/ml, respectively. In time-kill studies, daptomycin showed rapid and concentration-dependent killing of MRSA in stationary growth phase. At concentrations above 20 μg/ml, daptomycin reduced the counts by >3 log10 CFU/ml in 2 to 4 h. In sterile cage fluid, daptomycin peak concentrations of 23.1, 46.3, and 53.7 μg/ml were reached 4 to 6 h after the administration of single intraperitoneal doses of 20, 30, and 40 mg/kg of body weight, respectively. In treatment studies, daptomycin alone reduced the planktonic MRSA counts by 0.3 log10 CFU/ml, whereas in combination with rifampin, a reduction in the counts of >6 log10 CFU/ml was observed. Vancomycin and daptomycin (at both doses) were unable to cure any cage-associated infection when they were given as monotherapy, whereas rifampin alone cured the infections in 33% of the cages. In combination with rifampin, daptomycin showed cure rates of 25% (at 20 mg/kg) and 67% (at 30 mg/kg), vancomycin showed a cure rate of 8%, linezolid showed a cure rate of 0%, and levofloxacin showed a cure rate of 58%. In addition, daptomycin at a high dose (30 mg/kg) completely prevented the emergence of rifampin resistance in planktonic and adherent MRSA cells. Daptomycin at a high dose, corresponding to 6 mg/kg in humans, in combination with rifampin showed the highest activity against planktonic and adherent MRSA. Daptomycin plus rifampin is a promising treatment option for implant-associated MRSA infections.
doi:10.1128/AAC.00047-09
PMCID: PMC2704655  PMID: 19364845
25.  Daptomycin Antibiotic Lock Therapy in a Rat Model of Staphylococcal Central Venous Catheter Biofilm Infections▿ 
Antibiotic lock therapy (ALT) is an adjunctive procedure to prevent or treat central venous catheter infections, ensuing catheter-related bacteremia, and catheter-related metastatic infections. Daptomycin is a cyclic lipopeptide that is rapidly bactericidal against methicillin-susceptible and -resistant Staphylococcus aureus. The efficacies of daptomycin against central venous catheter biofilms, catheter-related bacteremia, and catheter-related metastatic infections were evaluated by adapting a previously reported central venous catheter biofilm model in rats. Combined daptomycin ALT and systemic dosing resulted in the clearance of an established in vivo S. aureus central venous catheter biofilm after just two daily ALT treatments (30 min with daptomycin at 5 mg/ml) with concurrent systemic daptomycin dosing (40 mg/kg of body weight/day subcutaneously [s.c.]; equivalent exposure of 6 mg/kg/day in people). Daptomycin ALT solutions formulated in either saline or lactated Ringer's solution were equally fast in eradicating established in vivo methicillin-resistant Staphylococcus epidermidis (MRSE) central venous catheter biofilms. However, the lactated Ringer's formulation was superior to that of saline in sustaining the bacterial clearance of treated central venous catheters (83% versus 50%). In MRSE-infected central venous catheter studies, 3 days of daptomycin or vancomycin ALT (18 h at 5 mg/ml) with systemic s.c. dosing (40 mg/kg/day daptomycin or 100 mg/kg/day vancomycin) was equally effective 1 week posttherapy in maintaining cleared central venous catheters (90% [n = 10] versus 100% [n = 8]). These results suggest that daptomycin ALT, along with systemic dosing, could be an effective treatment option for the prevention or eradication of staphylococcal central venous catheter biofilm infections, thereby reducing the occurrence of catheter-related bacteremia or catheter-related metastatic infections.
doi:10.1128/AAC.00147-11
PMCID: PMC3165291  PMID: 21709082

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