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1.  Etravirine in CSF is highly protein bound 
Etravirine has high affinity for plasma drug-binding proteins, such as albumin and α1-acid glycoprotein, which limits the amount of unbound etravirine available to enter the CNS. The objective of this study was to compare total and unbound etravirine concentrations in CSF with plasma concentrations and the in vitro median inhibitory concentration (IC50) for wild-type HIV (0.9 ng/mL).
Total and bound etravirine concentrations were measured in 17 CSF and plasma pairs by isotope-dilution liquid chromatography tandem mass spectroscopy, radioligand displacement and ultracentrifugation. Unbound etravirine concentrations were calculated from the bound fraction. The dynamic range of the assay was 7.8–2000 (plasma) and 0.78–200 (CSF) ng/mL.
Subjects were mostly middle-aged (median 43 years) white (78%) men (89%). All CSF etravirine concentrations were above the limit of quantification. Total and unbound median etravirine concentrations in CSF were 9.5 (IQR 6.4, 26.4) and 0.13 (IQR 0.08, 0.27) ng/mL, respectively. Etravirine was 96% (IQR 94.5, 97.2) protein bound in plasma and 98.4% (IQR 97.8, 98.8) in CSF. Total etravirine in CSF was 4.3% (IQR 3, 5.9) of total and 101% (IQR 76, 160) of unbound etravirine in plasma. There were no significant correlations between unbound etravirine concentrations and concentrations of albumin in plasma or CSF. Unbound etravirine concentrations in CSF did not reach the wild-type IC50 in any of the specimens.
Unbound etravirine may not achieve optimal concentrations to inhibit HIV replication in the CNS.
PMCID: PMC3625433  PMID: 23335197
HIV; antiretroviral therapy; central nervous system; CNS; protein binding; CSF
2.  Efavirenz concentrations in CSF exceed IC50 for wild-type HIV 
HIV-associated neurocognitive disorders remain common despite use of potent antiretroviral therapy (ART). Ongoing viral replication due to poor distribution of antivirals into the CNS may increase risk for HIV-associated neurocognitive disorders. This study's objective was to determine penetration of a commonly prescribed antiretroviral drug, efavirenz, into CSF.
CHARTER is an ongoing, North American, multicentre, observational study to determine the effects of ART on HIV-associated neurological disease. Single random plasma and CSF samples were drawn within 1 h of each other from subjects taking efavirenz between September 2003 and July 2007. Samples were assayed by HPLC or HPLC/mass spectrometry with detection limits of 39 ng/mL (plasma) and <0.1 ng/mL (CSF).
Eighty participants (age 44 ± 8 years; 79 ± 15 kg; 20 females) had samples drawn 12.5 ± 5.4 h post-dose. The median efavirenz concentrations after a median of 7 months [interquartile range (IQR) 2–17] of therapy were 2145 ng/mL in plasma (IQR 1384–4423) and 13.9 ng/mL in CSF (IQR 4.1–21.2). The CSF/plasma concentration ratio from paired samples drawn within 1 h of each other was 0.005 (IQR 0.0026–0.0076; n = 69). The CSF/IC50 ratio was 26 (IQR 8–41) using the published IC50 for wild-type HIV (0.51 ng/mL). Two CSF samples had concentrations below the efavirenz IC50 for wild-type HIV.
Efavirenz concentrations in the CSF are only 0.5% of plasma concentrations but exceed the wild-type IC50 in nearly all individuals. Since CSF drug concentrations reflect those in brain interstitial fluids, efavirenz reaches therapeutic concentrations in brain tissue.
PMCID: PMC3019085  PMID: 21098541
CNS; pharmacology; non-nucleoside reverse transcriptase inhibitors
4.  Population Pharmacokinetics of Intravenous Acyclovir in Preterm and Term Infants 
Acyclovir is used to treat herpes infections in preterm and term infants; however, the influence of maturation on drug disposition and dosing requirements is poorly characterized in this population.
We administered intravenous acyclovir to preterm and term infants <31 days postnatal age and collected plasma samples. We performed a population pharmacokinetic analysis. The primary pharmacodynamic target was acyclovir concentration ≥3 mg/L for ≥50% of the dosing interval. The final model was simulated using infant data from a clinical database.
The analysis included 28 infants (median 30 weeks gestation). Acyclovir pharmacokinetics was described by a 1-compartment model: clearance (L/h/kg) = 0.305 × (postmenstrual age [PMA]/31.3 weeks)3.02. This equation predicts a 4.5-fold increase in clearance from 25 to 41 weeks PMA. With proposed dosing, the pharmacodynamic target was achieved in 91% of infants: 20 mg/kg every 12 hours in infants <30 weeks PMA; 20 mg/kg every 8 hours in infants 30 to <36 weeks PMA; 20 mg/kg every 6 hours in infants 36–41 weeks PMA.
Acyclovir clearance increased with infant maturation. A dosing strategy based on PMA accounted for developmental changes in acyclovir disposition to achieve the surrogate pharmacodynamic target in the majority of infants.
PMCID: PMC3904301  PMID: 24346595
herpes simplex virus; preterm infants; acyclovir
5.  Intestinal Fatty-Acid Binding Protein and Metronidazole Response in Premature Infants 
In premature infants with suspected intra-abdominal infection, biomarkers for treatment response to antimicrobial therapy are lacking. Intestinal fatty acid-binding protein (I-FABP) is specific to the enterocyte and is released in response to intestinal mucosal injury. I-FABP has not been evaluated as a surrogate marker of disease response to antimicrobial therapy. We examined the relationship between metronidazole exposure and urinary I-FABP concentrations in premature infants with suspected intra-abdominal infection.
Study design
We conducted an intravenous metronidazole pharmacokinetic study, collecting ≤3 urine samples per infant for I-FABP concentration measurements. We analyzed the relationship between I-FABP concentrations and measures of metronidazole exposure and pharmacokinetics, maturational factors, and other covariates.
Twenty-six samples from 19 premature infants were obtained during metronidazole treatment. When analyzed without regard to presence of necrotic gastrointestinal disease, there were no significant associations between predictor variables and I-FABP concentrations. However, when the sample was limited to premature infants with necrotic gastrointestinal disease, an association was found between average predicted metronidazole concentration and I-FABP concentration (p=0.006).
While a predictive association between urinary I-FABP and metronidazole systemic exposure was not observed, the data suggest the potential of this endogenous biomarker to serve as a pharmacodynamic surrogate for antimicrobial treatment of serious abdominal infections in neonates and infants.
PMCID: PMC4225165  PMID: 25318626
necrotizing enterocolitis; biomarkers; pharmacokinetics; premature infants; antimicrobial agents
6.  Characterization of the Population Pharmacokinetics of Ampicillin in Neonates Using an Opportunistic Study Design 
Although ampicillin is the most commonly used drug in neonates, developmental pharmacokinetic (PK) data to guide dosing are lacking. Ampicillin is primarily renally eliminated, and developmental changes are expected to influence PK. We conducted an open-label, multicenter, opportunistic, prospective PK study of ampicillin in neonates stratified by gestational age (GA) (≤34 or >34 weeks) and postnatal age (PNA) (≤7 or >7 days). Drug concentrations were measured by tandem mass spectrometry. PK data were analyzed using population nonlinear mixed-effects modeling in NONMEM 7.2. Monte Carlo simulations were conducted to determine the probability of target attainment for the time in which the total steady-state ampicillin concentrations remained above the MIC (T>MIC) for 50%, 75%, and 100% of the dosing interval. A total of 142 PK samples from 73 neonates were analyzed (median [range] GA, 36 [24 to 41] weeks; PNA, 5 [0 to 25] days). The median ampicillin dose was 200 (100 to 350) mg/kg/day. Postmenstrual age and serum creatinine were covariates for ampicillin clearance (CL). A simplified dosing regimen of 50 mg/kg every 12 h for GA of ≤34 weeks and PNA of ≤7 days, 75 mg/kg every 12 h for GA of ≤34 weeks and PNA of ≥8 and ≤28 days, and 50 mg/kg every 8 h for GA of >34 weeks and PNA of ≤28 days achieved the prespecified surrogate efficacy target in 90% of simulated subjects. Ampicillin CL was associated with neonatal development. A simplified dosing regimen stratified by GA and PNA achieves the desired surrogate therapeutic target in the vast majority of neonates.
PMCID: PMC4068432  PMID: 24614374
7.  Developmental Pharmacokinetics of Piperacillin and Tazobactam Using Plasma and Dried Blood Spots from Infants 
Piperacillin-tazobactam is often given to infants with severe infection in spite of limited pharmacokinetics (PK) data. We evaluated piperacillin-tazobactam PK in premature and term infants of ages <61 days with suspected systemic infection. Infants received intravenous piperacillin-tazobactam (80 to 100 mg/kg of body weight every 8 h [q 8 h]) based on gestational and postnatal age. Sparse plasma samples were obtained after first and multiple doses. Drug concentrations were measured by tandem mass spectrometry. PK data were analyzed using population nonlinear mixed-effect modeling. Target attainment rates for the time unbound piperacillin concentrations remained above the MIC for 50% and 75% of the dosing interval at steady state were evaluated. Bias in population PK parameter estimates was assessed for dried blood spot (DBS) samples, and a comparability analysis was performed for DBS and plasma drug concentrations using linear regression. We obtained 128 plasma samples from 32 infants, median gestational age of 30 weeks (range, 23 to 40 weeks) and postnatal age of 8 days (range, 1 to 60). Piperacillin and tazobactam PK models included body weight (WT) and postmenstrual age (PMA) as covariates for clearance and WT for volume of distribution and were used to optimize dosing in infants. DBS drug concentrations were 50 to 60% lower than those in plasma, but when combined with plasma concentrations and a matrix effect, the data generated PK model parameters similar to those for plasma alone. With PMA-based dosing (100 mg/kg q 8 h, 80 mg/kg q 6 h, and 80 mg/kg q 4 h for PMA of ≤30, 30 to 35, and 35 to 49 weeks, respectively), 90% of simulated infants achieved the surrogate therapeutic target of time above the MIC (≤32 mg/liter) for 75% of the dosing interval.
PMCID: PMC3993246  PMID: 24614369
8.  Population-Based Pharmacokinetic Modeling of Vancomycin in Children with Renal Insufficiency 
Vancomycin dosing to achieve the area-under-the-curve to minimum inhibitory concentration (AUC/MIC) target of ≥ 400 in children with renal insufficiency is unknown. Our objectives were to compare vancomycin clearance (CL) and initial dosing in children with normal and impaired renal function.
Using a matched case-control study in subjects ≥ 3 months old who received vancomycin ≥ 48 hr, we performed population-based modeling with empiric Bayesian post-hoc individual parameter estimations and Monte Carlo simulations. Cases, defined by baseline serum creatinine (SCr) ≥ 0.9 mg/dL, were matched 1:1 to controls by age and weight.
Analysis included 63 matched pairs with 319 serum concentrations. Mean age (± SD) was 13 ± 6 yr and weight, 51 ± 25 kg. Mean baseline SCr was 0.6 ± 0.2 mg/dL for controls, and 1.3 ± 0.5 for cases. Age, SCr, and weight were independent covariates for CL. Final model parameters and inter-subject variability (ISV) were: CL(L/hr) = 0.235*Weight0.75*(0.64/SCr)0.497*(ln(DOL)/8.6)1.19 ISV=39%, where DOL is day of life. Target AUC/MIC ≥ 400 was achieved in 80% of cases at vancomycin 45 mg/kg/day, but required 60 mg/kg/day for controls. Drug CL improved in 87% of cases due to recovery of renal function.
Due to reduced CL, a less frequent dosing at 15 mg/kg every 8 hr (i.e., 45 mg/kg/day) may be appropriate for some children with renal impairment. Close monitoring of renal function and drug concentrations is prudent to ensure adequate drug exposure, especially in those with renal impairment since recovery of renal function may occur during therapy.
PMCID: PMC4191860  PMID: 25309945
Vancomycin; Children; Pediatrics; Renal disease; Renal insufficiency; Antibiotic; Methicillin-resistant Staphylococcus aureus (MRSA); Staphylococcus aureus; Antibiotic resistance; Pharmacokinetic-pharmacodynamic; Population-based pharmacokinetic modeling; Monte Carlo simulation; Area-under-the curve
9.  Determining Population and Developmental Pharmacokinetics of Metronidazole Using Plasma and Dried Blood Spot Samples from Premature Infants 
Limited pharmacokinetic (PK) data of metronidazole in premature infants has led to various dosing recommendations. Surrogate efficacy targets for metronidazole are ill-defined and therefore aimed to exceed minimum inhibitory concentration of organisms responsible for intra-abdominal infections.
We evaluated the PK of metronidazole using plasma and dried blood spot (DBS) samples from infants ≤32 weeks gestational age in an open-label, PK, multicenter (N=3) study using population PK modeling (NONMEM). Monte Carlo simulations (N=1000 virtual subjects) were used to evaluate the surrogate efficacy target. Metabolic ratios of parent and metabolite were calculated.
Twenty-four premature infants (111 plasma and 51 DBS samples) were enrolled: median (range) gestational age at birth 25 (23–31) weeks, postnatal age 27 (1–82) days, postmenstrual age (PMA) 31 (24–39) weeks, and weight 740 (431–1466) g. Population clearance (CL, L/h/kg) was 0.038 × (PMA/30)2.45 and volume of distribution (L/kg) of 0.93. PK parameter estimates and precision were similar between plasma and DBS samples. Metabolic ratios correlated with CL.
Simulations suggested the majority of infants in the neonatal intensive care unit (>80%) would meet the surrogate efficacy target using PMA-based dosing.
PMCID: PMC3769518  PMID: 23587979
neonate; drug; pharmacokinetics; metronidazole; dried blood spots
10.  Auranofin Is Highly Efficacious against Toxoplasma gondii In Vitro and in an In Vivo Experimental Model of Acute Toxoplasmosis 
The mainstay of toxoplasmosis treatment targets the folate biosynthetic pathways and has not changed for the last 50 years. The activity of these chemotherapeutic agents is restricted to one lifecycle stage of Toxoplasma gondii, they have significant toxicity, and the impending threat of emerging resistance to these agents makes the discovery of new therapies a priority. We now demonstrate that auranofin, an orally administered gold containing compound that was FDA approved for treatment of rheumatoid arthritis, has activity against Toxoplasma gondii in vitro (IC50 = 0.28 µM) and in vivo (1 mg/kg).
Methods/Principal Findings
Replication within human foreskin fibroblasts of RH tachyzoites was inhibited by auranofin. At 0.4 µM, auranofin inhibited replication, as measured by percent infected fibroblasts at 24 hrs, (10.94% vs. 24.66% of controls; p = 0.0003) with no effect on parasite invasion (16.95% vs. 12.91% p = 0.4331). After 18 hrs, 62% of extracellular parasites treated with auranofin were non-viable compared to control using an ATP viability assay (p = 0.0003). In vivo, a previously standardized chicken embryo model of acute toxoplasmosis was used. Fourteen day old chicken embryos were injected through the chorioallantoic vein with 1×104 tachyzoites of the virulent RH strain. The treatment group received one dose of auranofin at the time of inoculation (1 mg/kg estimated body weight). On day 5, auranofin-treated chicken embryos were 100% protected against death (p = 0.0002) and had a significantly reduced parasite load as determined by histopathology, immunohistochemistry and by the number of parasites quantified by real-time PCR.
These results reveal in vitro and in vivo activity of auranofin against T. gondii, suggesting that it may be an effective alternative treatment for toxoplasmosis.
Author Summary
Toxoplasma gondii is a protozoan parasite that infects at least two thirds of the world human population. Once it infects the human host, it has great predilection for the brain and the retina of the eye. It remains latent until the host's immune system weakens, and then causes organ tissue damage. There are very few treatments available that are active against this parasite, and they all fail to eradicate it from the human body. Hence, there is always a risk for recurrence and/or disabling long-term complications such as blindness or neurological abnormalities. Despite this fact, it has been over fifty years since most anti-Toxoplasma agents were initially described. Most recently, in an attempt to expedite the process of drug discovery, older drugs are making a comeback by being re-purposed for new diseases. Auranofin, which was originally designed to treat rheumatoid arthritis, has consistently shown antiparasitic activity against multiple organisms, including parasites of great public health importance such as Plasmodium, Schistosoma and Leishmania, although most of these reports are based on in vitro assays. Herein, we present our studies that demonstrate that auranofin is active against Toxoplasma gondii in vitro and in an animal model of acute Toxoplasma infection, suggesting that auranofin has great potential to become a new anti-Toxoplasma agent.
PMCID: PMC4117455  PMID: 25079790
11.  Adverse Events Associated with Meropenem versus Imipenem/Cilastatin Therapy in a Large Retrospective Cohort of Hospitalized Infants 
Carbapenems are commonly used in hospitalized infants despite a lack of complete safety data and associations with seizures in older children. We compared the incidence of adverse events in hospitalized infants receiving meropenem versus imipenem/cilastatin.
We conducted a retrospective cohort study of 5566 infants treated with meropenem or imipenem/cilastatin in neonatal intensive care units managed by the Pediatrix Medical Group between 1997 and 2010. Multivariable conditional logistic regression was performed to evaluate the association between carbapenem therapy and adverse events, controlling for infant factors and severity of illness.
Adverse events were more common with use of meropenem compared with imipenem/cilastatin (62.8/1000 infant days vs. 40.7/1000 infant days, P<0.001). There was no difference in seizures with meropenem vs. imipenem/cilastatin (adjusted odds ratio [OR] 0.96; 95% confidence interval 0.68, 1.32). The incidence of death, as well as the combined outcome of death or seizure, was lower with meropenem use—OR 0.68 (0.50, 0.88) and OR 0.77 (0.62, 0.95), respectively.
In this cohort of infants, meropenem was associated with more frequent but less severe adverse events when compared with imipenem/cilastatin.
PMCID: PMC3708263  PMID: 23838776
meropenem; imipenem/cilastatin; adverse events; infant
13.  Improved Vancomycin Dosing in Children Using Area-Under-the-Curve Exposure 
Our objectives were to: (1) determine the pharmacokinetic [PK] indices of vancomycin in pediatric patients; and (2) compare attainment of two target exposures: AUC/MIC ≥ 400 and trough concentration ≥ 15 mcg/mL.
The population-based PK modeling was performed using NONMEM 7.2 for children ≥ 3 months old who received vancomycin for ≥ 48 hr from 2003 to 2011. A one-compartment model with first-order kinetics was used to estimate clearance (CL), volume of distribution (Vd) and area-under-curve (AUC). Empiric Bayesian post-hoc individual parameters and Monte Carlo simulations (N=11,000) were performed.
Analysis included 702 patients with 1660 vancomycin serum concentrations. Median age was 6.6 (interquartile range [IQR] 2.2–13.4) yr, weight 22.7 (12.6–46) kg, and baseline serum creatinine (SCr) 0.40 (0.30–0.60) mg/dL. Final model PK indices were: CL(L/h) = 0.248*Wt0.75*(0.48/SCr)0.361*(ln(age)/7.8)0.995; and Vd(L) = 0.636*Wt. Using these parameters and the observed MIC distribution, Monte Carlo simulation indicated that the initial median dose of 44 (39–52) mg/kg/day was inadequate in most subjects. Regimens of 60 mg/kg/day for subjects ≥ 12 years old and 70 mg/kg/day for those < 12 years old achieved target AUC/MIC in ~ 75% and trough concentrations ≥ 15 in ~ 45% of virtual subjects. An AUC/MIC ~ 400 corresponded to trough concentration ~ 8 to 9 mcg/mL.
Targeted exposure using vancomycin AUC/MIC, compared with trough concentrations, is a more realistic target in children. Depending on age, serum creatinine, and MIC distribution, vancomycin in a dosage of 60 to 70 mg/kg/day was necessary to achieve AUC/MIC ≥ 400 in 75% of patients.
PMCID: PMC3632448  PMID: 23340565
Vancomycin; children; pediatrics; antibiotic; Staphylococcus aureus; pharmacokinetic; pharmacodynamic
14.  Determination of Efavirenz in Human Dried Blood Spots by Reversed-Phase High Performance Liquid Chromatography with UV Detection 
Therapeutic drug monitoring  2013;35(2):10.1097/FTD.0b013e31827fb72b.
Previously published methods for determination of efavirenz (EFV) in human dried blood spots (DBS) employ costly and complex liquid chromatography/mass spectrometry. We describe the validation and evaluation of a simple and inexpensive high-performance liquid chromatography (HPLC) method for EFV quantification in human DBS and dried plasma spots (DPS), using ultraviolet (UV) detection appropriate for resource-limited settings.
100μl of heparinized whole blood or plasma were spotted onto blood collection cards, dried, punched, and eluted. Eluates are injected onto a C-18 reversed phase HPLC column. EFV is separated isocratically using a potassium phosphate and ACN mobile phase. UV detection is at 245nm. Quantitation is by use of external calibration standards. Following validation, the method was evaluated using whole blood and plasma from HIV-positive patients undergoing EFV therapy.
Mean recovery of drug from dried blood spots is 91.5%. The method is linear over the validated concentration range of 0.3125 – 20.0μg/mL. A good correlation (Spearman r=0.96) between paired plasma and DBS EFV concentrations from the clinical samples was observed, and hematocrit level was not found to be a significant determinant of the EFV DBS level. The mean observed CDBS/Cplasma ratio was 0.68. A good correlation (Spearman r=0.96) between paired plasma and DPS EFV concentrations from the clinical samples was observed. The mean percent deviation of DPS samples from plasma samples is 1.68%.
Dried whole blood spot or dried plasma spot sampling is well suited for monitoring EFV therapy in resource limited settings, particularly when high sensitivity is not essential.
PMCID: PMC3848783  PMID: 23503446
Efavirenz; Dried Blood Spots; Dried Plasma Spots; HPLC
15.  Darunavir is predominantly unbound to protein in cerebrospinal fluid and concentrations exceed the wild-type HIV-1 median 90% inhibitory concentration 
Higher CSF antiretroviral concentrations may be associated with better control of HIV replication and neurocognitive performance, but only the unbound fraction of antiretrovirals is available to inhibit HIV. Therefore, the objective of this study was to determine total and unbound darunavir concentrations in CSF and compare findings with plasma concentrations as well as the wild-type HIV-1 90% inhibitory concentration (IC90).
Subjects with HIV infection were selected based on the use of darunavir-containing regimens with a twice-daily dosing schedule and availability of stored CSF and matched plasma. Total darunavir was measured by HPLC for plasma or liquid chromatography–tandem mass spectroscopy (LC/MS/MS) for CSF. Plasma unbound darunavir was measured by ultrafiltration and LC/MS/MS. CSF protein binding was determined by competitive binding exchange with radiolabelled darunavir.
Twenty-nine matched CSF–plasma pairs were analysed and darunavir was detected in all CSF specimens (median total concentration 55.8 ng/mL), with a CSF unbound fraction of 93.5%. Median fractional penetrance was 1.4% of median total and 9.4% of median unbound plasma concentrations. Unbound darunavir concentrations in CSF exceeded the median IC90 for wild-type HIV in all subjects by a median of 20.6-fold, despite the relatively low fractional penetrance. Total darunavir concentrations in CSF correlated with both total and unbound darunavir concentrations in plasma.
Darunavir should contribute to the control of HIV replication in the CNS as a component of effective combination antiretroviral regimens.
PMCID: PMC3566670  PMID: 23143899
HIV; antiretroviral therapy; central nervous system; protein binding
16.  Lopinavir Exposure With an Increased Dose During Pregnancy 
Use of standard adult lopinavir/ritonavir (LPV/RTV) dosing (400/100 mg) during the third trimester of pregnancy results in reduced LPV exposure. The goal of this study was to determine LPV exposure during the third trimester of pregnancy and 2 weeks postpartum with a higher LPV/RTV dose.
The Pediatric AIDS Clinical Trials Group Protocol 1026s is an ongoing, prospective, nonblinded study of antiretroviral pharmacokinetics in HIV-infected pregnant women that included a cohort receiving LPV/RTV 400/100 mg twice daily during the second trimester and 533/133 mg twice daily during the third trimester through 2 weeks postpartum. Intensive steady state 12-hour pharmacokinetic profiles were performed during the third trimester and at 2 weeks postpartum and were optional during the second trimester. LPV and RTV were measured by reverse-phase high-performance liquid chromatography with a detection limit of 0.09 µg/mL.
Twenty-six HIV-infected pregnant women were studied. Median LPV area under the plasma concentration-time curve (AUCs) for the second trimester, third trimester, and postpartum were 57, 88, and 152 µg·h−1·mL−1, respectively. Median minimum LPV concentrations were 1.9, 4.1, and 8.3 µg/mL.
The higher LPV/RTV dose (533/133 mg) provided LPV exposure during the third trimester similar to the median AUC (80 µg·h−1·mL−1) in nonpregnant adults taking standard doses. However, the AUC on this increased dose at 2 weeks postpartum was considerably higher. These data suggest that the higher LPV/RTV dose should be used in third trimester pregnant women; that it should be considered in second trimester pregnant women, especially those who are protease inhibitor experienced; and that postpartum LPV/RTV dosing can be reduced to standard dosing by 2 weeks after delivery.
PMCID: PMC3912695  PMID: 18989231
HIV; lopinavir; mother-to-child transmission; pharmacokinetics; pregnancy
17.  Developmental Pharmacokinetic Changes of Lamivudine in Infants and Children 
Journal of clinical pharmacology  2011;52(12):1824-1832.
Lamivudine is a nucleoside reverse transcriptase inhibitor widely used in infants and children in combination antiretroviral therapy to treat human immunodeficiency virus (HIV) infection. Developmental changes in lamivudine pharmacokinetic disposition were assessed by combining data from 7 studies of lamivudine (Pediatric AIDS Clinical Trials Group 300, 353, 356, 358, 386, 1056, and 1069) representing subjects across the pediatric age continuum. A population pharmacokinetic model was developed to identify factors that influence lamivudine disposition. Age and Thai race were independent predictors of apparent clearance (CL/F), whereas the use of a fixed drug combination formulation (GPO-VIR) was an independent predictor of bioavailability, with CL/F more than doubling from birth to adolescence. Serum creatinine was not associated with CL/F. Monte Carlo simulations were used to compare the lamivudine exposure achieved with World Health Organization (WHO) weight band and Food and Drug Administration (FDA) label dosing recommendations. WHO dosing yielded higher exposure during the first few months of life, but this difference was less pronounced between 6 months and 14 years of age. Overall, both FDA and WHO dosing provided similar AUC values to those previously reported in HIV-infected adults. Lamivudine WHO weight band dosing results in therapeutic exposure in infants and children and may improve drug dosing in resource-limited countries.
PMCID: PMC3369109  PMID: 22180560
Clinical research; infectious diseases; pediatrics; pharmacokinetics and drug metabolism; virology
18.  Safety and Effectiveness of Meropenem in Infants With Suspected or Complicated Intra-abdominal Infections 
The safety and effectiveness of meropenem in young infants with suspected or confirmed intra-abdominal infections were evaluated. was well tolerated in this cohort of critically-ill infants, and the majority of infants treated with meropenem (84%) met the definition of therapeutic success.
Background. Intra-abdominal infections are common in young infants and lead to significant morbidity and mortality. Meropenem is a broad-spectrum antimicrobial with excellent activity against pathogens associated with intra-abdominal infections. The purpose of this study was to determine the safety and effectiveness of meropenem in young infants with suspected or complicated intra-abdominal infections.
Methods. Preterm and term infants <91 days of age with suspected or confirmed intra-abdominal infections hospitalized in 24 neonatal intensive care units were studied in an open-label, multiple-dose study. Adverse events and serious adverse events were collected through 3 and 30 days following the last meropenem dose, respectively. Effectiveness was assessed by 3 criteria: death, bacterial cultures, and presumptive clinical cure score.
Results. Of 200 subjects enrolled in the study, 99 (50%) experienced an adverse event, and 34 (17%) had serious adverse events; no adverse events were probably or definitely related to meropenem. The most commonly reported adverse events were sepsis (6%), seizures (5%), elevated conjugated bilirubin (5%), and hypokalemia (5%). Only 2 of the serious adverse events were determined to be possibly related to meropenem (isolated ileal perforation and an episode of fungal sepsis). Effectiveness was evaluable in 192 (96%) subjects, and overall treatment success was 84%.
Conclusions. Meropenem was well tolerated in this cohort of critically ill infants, and the majority of infants treated with meropenem met the definition of therapeutic success.
Clinical Trials Registration. NCT00621192.
PMCID: PMC3491861  PMID: 22955430
19.  Pharmacokinetics and Safety of Fluconazole in Young Infants Supported with Extracorporeal Membrane Oxygenation 
Candida infections are a leading cause of infectious disease-related death in infants supported with extracorporeal membrane oxygenation (ECMO). The ECMO circuit can alter drug pharmacokinetics (PK), thus standard fluconazole dosing in children on ECMO may result in suboptimal drug exposure. This study determined the PK of fluconazole in infants on ECMO.
Infants <120 days old received either intravenous fluconazole prophylaxis (25 mg/kg once a week) or treatment (12 mg/kg daily) while on ECMO. Paired plasma samples were collected pre- and post-oxygenator around doses 1 and 2 to calculate PK indices and describe oxygenator extraction. A 1-compartment model was fit to the data using non-linear regression. Surrogate pharmacodynamic targets for efficacy were evaluated.
Ten infants were enrolled. After dose 1 (n=9), the median clearance was 17 mL/kg/h, the median volume of distribution was 1.5 L/kg, and the median exposure in the first 24 hours (AUC0–24) was 322 h*mg/L. After multiple doses (n=7), the median clearance was 22 mL/kg/h, the median volume of distribution was 1.9 L/kg, and the AUC0–24 was 352 h*mg/L. After dose 1, 78% of infants achieved the prophylaxis target, while only 11% achieved the therapeutic target. Oxygenator extraction of fluconazole was minimal (−2.0%, standard deviation 15.0), and extraction was not correlated with age of the ECMO circuit (rho= − 0.05). There were no adverse events related to fluconazole.
Infants on ECMO had higher volume of distribution but similar clearance when compared with historical controls not on ECMO. In infants on ECMO, a fluconazole dose of 25 mg/kg weekly provides adequate exposure for prophylaxis against Candida infections. However, higher doses may be needed for treatment.
PMCID: PMC3444624  PMID: 22627870
fluconazole; Candida; extracorporeal membrane oxygenation; pharmacokinetics; infants
20.  Dynamics of the resting CD4+ T-cell latent HIV reservoir in infants initiating HAART less than 6 months of age 
AIDS (London, England)  2012;26(12):1483-1490.
Identification of HIV infection in exposed infants facilitates early therapy, which may limit viral reservoirs that maintain HIV infection under HAART.
The dynamics of the resting CD4+ T-cell latent HIV reservoir was determined over the first 2 years of life in 17 HIV-infected infants initiating lopinavir/ritonavir-based HAART at a median age of 8.1 weeks and achieving adequate suppression of plasma viral load by 24 weeks.
The resting CD4+ T-cell latent HIV reservoir was detected in 12 of 14 (86%) infants tested at 24 weeks of HAART [median frequency 1.88 infectious units per million (IUPM); range <0.22 to 81.7), and remained measurable (median IUPM =0.32; range < 0.22 to 3.25) in six of 10 (60%) children retested at 96 weeks. The reservoir declined, from 24 to 96 weeks of HAART, at an estimated mean rate of 0.028 log10 IUPM/month, corresponding to a half-life of 11 months (95% confidence interval 6–30 months]. A strong relationship was found between the frequency of latently infected CD4+T cells at 96 weeks of HAART and time to first undetectable plasma viral load (Spearman r =0.91, P <0.001).
Although the resting CD4+ T-cell latent reservoir remains detectable over the first 2 years of HAART in a substantial proportion of infants, its size is associated with time to first undetectable viral load. To minimize HIV reservoirs in infants, rapid curtailment of viremia may limit HIV reservoirs and should be a therapeutic goal of early HAART in infants.
PMCID: PMC3495308  PMID: 22555165
early HAART; infants; latent reservoir dynamics
21.  High Dose of Darunavir in Treatment-experienced HIV-infected Adolescent Results in Virologic Suppression and Improved CD4 Count 
Therapeutic Drug Monitoring  2012;34(3):237-241.
We describe an unintentional significant overdose of darunavir in a treatment-experienced adolescent with decreased darunavir susceptibility and prior treatment failure on darunavir therapy. Minimal toxicity and improved virologic suppression observed with an overdose have prompted consideration of the continued use of higher than recommended dose. Pharmacokinetic and pharmacodynamic evaluations justified the individualized use of high-dose darunavir, which resulted in virologic suppression, improved CD4 count and resolution of toxicity.
PMCID: PMC3354040  PMID: 22549499
Darunavir;  Adolescent; Pharmacokinetics; Safety; HIV
22.  The pharmacokinetics of intravenous lorazepam in pediatric patients with and without status epilepticus 
The Journal of Pediatrics  2011;160(4):667-672.e2.
To evaluate the single dose pharmacokinetics of an intravenous dose of lorazepam in pediatric patients treated for status epilepticus (SE) or with a history of SE.
Study design
Ten hospitals in the Pediatric Emergency Care Applied Research Network (PECARN) enlisted patients 3 months to 17 years with convulsive SE (STATUS) or for a traditional PK study (ELECTIVE). Sparse sampling was used for STATUS and intensive sampling for ELECTIVE. Noncompartmental analyses were performed on ELECTIVE, and served to nest compartmental population PK analysis for both cohorts.
48 STATUS and 15 ELECTIVE patients were enrolled. Median age was 7 years, 2 months. The population PK parameters were: clearance 1.2 mL/min/kg, half-life 16.8 hours, volume of distribution 1.5 L/kg. Based on the PK model, a 0.1 mg/kg dose is expected to achieve concentrations of approximately 100 ng/mL and maintain concentrations above 30–50 ng/mL for 6–12 hours. A second dose of 0.05 mg/kg would achieve desired therapeutic serum levels for approximately 12 hours without excessive sedation. Age-dependent dosing is not necessary beyond using a maximum initial dose of 4 mg.
Lorazepam PK in convulsive status epilepticus is similar to previous PK measured in pediatric patients with cancer, except for longer half-life and similar to adult PK parameters except for increased clearance.
PMCID: PMC3274567  PMID: 22050870
23.  LOW CSF Concentrations of the Nucleotide HIV Reverse Transcriptase Inhibitor, Tenofovir 
Tenofovir is a nucleotide HIV reverse transcriptase inhibitor whose chemical properties suggest that it may not penetrate into the central nervous system in therapeutic concentrations. The study objective was to determine tenofovir penetration into cerebrospinal fluid (CSF).
CHARTER is a multi-center, observational study to determine effects of antiretroviral therapy on HIV-associated neurological disease. Single random plasma and CSF samples were drawn within an hour of each other from subjects taking tenofovir between October 2003 and March 2007. All samples were assayed by mass spectrometry with a detection limit of 0.9 ng/mL.
183 participants (age 44 ± 8 years; 83 ± 32 kg; 33 females; CSF protein 44 ± 16 mg/dL) had plasma and CSF samples drawn 12.2 ± 6.9 and 11 ± 7.8 hours post-dose respectively. Median plasma and CSF tenofovir concentrations were 96 ng/mL (IQR 47 – 153) and 5.5 ng/mL (IQR 2.7 – 11.3), respectively. Thirty-four of 231 (14.7%) plasma and 9/77 (11.7%) CSF samples were below detection. CSF/plasma concentration ratio from paired samples was 0.057 (IQR 0.03 – 0.1; n=38). Median CSF/wild-type IC50 ratio was 0.48 (IQR 0.24 – 0.98). Seventy-seven percent of CSF concentrations were below the tenofovir wild-type IC50. More subjects had detectable CSF HIV with lower (≤ 7 ng/mL) versus higher (> 7ng/mL) CSF tenofovir concentrations (29% vs. 9%; p=0.05).
Tenofovir concentrations in the CSF are only 5% of plasma concentrations, suggesting limited transfer into the CSF, and possibly active transport out of the CSF. CSF tenofovir concentrations may not effectively inhibit viral replication in the CSF.
PMCID: PMC3299895  PMID: 22217676
tenofovir; CSF; pharmacokinetics
24.  Nevirapine Exposure with WHO Pediatric Weight Band Dosing: Enhanced Therapeutic Concentrations Predicted Based on Extensive International Pharmacokinetic Experience 
Antimicrobial Agents and Chemotherapy  2012;56(10):5374-5380.
Nevirapine (NVP) is a nonnucleoside reverse transcriptase inhibitor (NNRTI) used worldwide as part of combination antiretroviral therapy in infants and children to treat HIV infection. Dosing based on either weight or body surface area has been approved by the U.S. Food and Drug Administration (FDA) but can be difficult to implement in resource-limited settings. The World Health Organization (WHO) has developed simplified weight band dosing for NVP, but it has not been critically evaluated. NVP pharmacokinetic data were combined from eight pediatric clinical trials (Pediatric AIDS Clinical Trials Group [PACTG] studies 245, 356, 366, 377, 403, 1056, and 1069 and Children with HIV in Africa Pharmacokinetics and Adherence of Simple Antiretroviral Regimens [CHAPAS]) representing subjects from multiple continents and across the pediatric age continuum. A population pharmacokinetic model was developed to characterize developmental changes in NVP disposition, identify potential sources of NVP pharmacokinetic variability, and assess various pediatric dosing strategies and their impact on NVP exposure. Age, CYP2B6 genotype, and ritonavir were independent predictors of oral NVP clearance. The Triomune fixed-dose tablet was an independent predictor of bioavailability compared to the liquid and other tablet formulations. Monte Carlo simulations of the final model were used to assess WHO weight band dosing recommendations. The final pharmacokinetic model indicated that WHO weight band dosing is likely to result in a percentage of children with NVP exposure within the target range similar to that obtained with FDA dosing. Weight band dosing of NVP proposed by the WHO has the potential to provide a simple and effective dosing strategy for resource limited settings.
PMCID: PMC3457371  PMID: 22869579
25.  Efavirenz Pharmacokinetics during the Third Trimester of Pregnancy and Postpartum 
The impact of pregnancy on efavirenz pharmacokinetics is unknown.
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 and a trough concentration of 1 mcg/mL.
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 (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.
Changes in efavirenz pharmacokinetics during pregnancy compared to postpartum are not sufficiently large enough to warrant a dose adjustment during pregnancy.
PMCID: PMC3288559  PMID: 22083071
efavirenz; pregnancy; pharmacokinetics; HIV; prevention of mother-to-child transmission of HIV

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