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1.  Impact of Granulocytes on the Antimicrobial Effect of Tedizolid in a Mouse Thigh Infection Model▿ 
Antimicrobial Agents and Chemotherapy  2011;55(11):5300-5305.
Tedizolid (TR-700, formerly torezolid) is the active component of the new oxazolidinone prodrug tedizolid phosphate (TR-701). We had previously demonstrated that tedizolid possessed potent antistaphylococcal activity superior to that of linezolid in a neutropenic mouse thigh infection model (A. Louie, W. Liu, R. Kulawy, and G. L. Drusano, Antimicrob. Agents Chemother. 55:3453-3460, 2011). In the current investigation, we used a mouse thigh infection model to delineate the effect of an interaction of TR-700 and granulocytes on staphylococcal cell killing. We compared the antistaphylococcal killing effect of doses of TR-701 equivalent to human exposures ranging from 200 to 3,200 mg/day in both granulocytopenic and normal mice. The mice were evaluated at 24, 48, and 72 h after therapy initiation. In granulocytopenic mice, a clear exposure response in which, depending on the time point of evaluation, stasis was achieved at “human-equivalent” doses of slightly below 2,300 mg/day (at 24 h) to slightly below 2,000 mg/day (at 72 h) was observed. In immune-normal animals, stasis was achieved at human-equivalent doses of slightly greater than 100 mg/day or less. The variance in bacterial cell killing results was attributable to the presence of granulocytes (without drug), the direct effect of TR-700 on Staphylococcus aureus, and the effect of the drug on Staphylococcus aureus mediated through granulocytes. The majority of the bacterial cell killing in normal animals was attributable to the effect of TR-700 mediated through granulocytes. Additional studies need to be undertaken to elucidate the mechanism underlying this observation.
PMCID: PMC3195040  PMID: 21911576
2.  Mutation in the sdeS Gene Promotes Expression of the sdeAB Efflux Pump Genes and Multidrug Resistance in Serratia marcescens▿ 
Serratia marcescens gained resistance to both biocides and antibiotics on expressing the SdeAB efflux pump, following exposure to increasingly higher concentrations of a biocide (H. Maseda et al., Antimicrob. Agents Chemother. 53:5230–5235, 2009). To reveal the regulatory mechanism of sdeAB expression, wild-type cells were subjected to transposon-mediated random mutagenesis, and a mutant with antibiotic resistance, which mimicked the phenotype of the previous biocide-resistant cells, was obtained. The transposon element was found in the chromosomal DNA downstream of the sdeAB operon. Sequencing revealed the presence of an open reading frame (ORF) encoding a protein with 159 amino acid residues that is highly similar to the BadM-type transcriptional repressor, designated sdeS. The level of sdeB::xylE reporter gene expression, undetectable in the wild-type cells, appeared to be fully comparable to that in the biocide-resistant cells. Nucleotide sequencing of the mutant revealed sdeS to have a single G-to-A base substitution at position 269 that converted Trp90 to a stop codon. Introduction of a plasmid-borne intact sdeS into the mutant cells and the biocide-resistant cells resulted in a reduction in sdeB::xylE reporter activity to an undetectable level. These results suggested that SdeS functions as a repressor of the sdeAB operon. It was concluded that the original biocide-resistant cells had an impaired sdeS and, therefore, a derepressed level of the SdeAB efflux pump.
PMCID: PMC3101466  PMID: 21422216
3.  Joint population pharmacokinetic analysis of zidovudine, lamivudine, and their active intracellular metabolites in HIV patients 
The population pharmacokinetic parameters of AZT and 3TC and their active intracellular metabolites were described from 75 naïve HIV infected patients receiving oral combination of AZT and 3TC twice daily, as part of their multitherapy treatment in the COPHAR2 – ANRS 111 trial. Four blood samples per patient were taken after two weeks of treatment to measure the concentration at steady state. Plasma AZT and 3TC concentrations were measured in 73 patients among those 62 patients had measurable intracellular AZT-TP and 3TC-TP concentrations. For each drug, a joint population pharmacokinetic model was developed and we investigated the influence of different covariates. We then studied correlations between mean plasma and intracellular concentrations of each drugs. A one compartment model with first order absorption and elimination best described plasma AZT concentration, with an additional compartment for intracellular AZT-TP. A similar model but with zero order absorption was found to adequately described concentrations of 3TC and its metabolite 3TC-TP. AZT and 3TC half-lives were 0.81 h (94.8%) and 2.97 h (39.2%), respectively whereas intracellular half-lives for AZT-TP and 3TC-TP were 10.73 h (69%) and 21.16 h (44%), respectively. We found particularly a gender effect on the apparent clearance of AZT as well as on mean plasma and intracellular concentrations of AZT, which were significantly higher in females than in males. Relationships between mean plasma and intracellular concentration were also highlighted both for AZT and for 3TC. Simulation with the model of plasma and intracellular concentrations for once versus twice daily regimens suggested that daily dosing regimen with double doses could be appropriate.
PMCID: PMC3122424  PMID: 21576446
Adult; Anti-HIV Agents; pharmacokinetics; Chromatography, Liquid; Cytidine Triphosphate; analogs & derivatives; pharmacokinetics; Dideoxynucleotides; pharmacokinetics; Female; Humans; Lamivudine; analogs & derivatives; pharmacokinetics; Male; Middle Aged; Models, Theoretical; Sex Factors; Tandem Mass Spectrometry; Young Adult; Zidovudine; pharmacokinetics
4.  Efficacy of a New Fluoroquinolone, JNJ-Q2, in Murine Models of Staphylococcus aureus and Streptococcus pneumoniae Skin, Respiratory, and Systemic Infections▿§ 
Antimicrobial Agents and Chemotherapy  2011;55(12):5522-5528.
The in vivo efficacy of JNJ-Q2, a new broad-spectrum fluoroquinolone (FQ), was evaluated in a murine septicemia model with methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) and in a Streptococcus pneumoniae lower respiratory tract infection model. JNJ-Q2 and comparators were also evaluated in an acute murine skin infection model using a community-acquired MRSA strain and in an established skin infection (ESI) model using a hospital-acquired strain, for which the selection of resistant mutants was also determined. JNJ-Q2 demonstrated activity in the MSSA septicemia model that was comparable to that moxifloxacin (JNJ-Q2 50% effective dose [ED50], 0.2 mg/kg of body weight administered subcutaneously [s.c.] and 2 mg/kg administered orally [p.o.]) and activity in the MRSA septicemia model that was superior to that of vancomycin (JNJ-Q2 ED50, 1.6 mg/kg administered s.c.). In an S. pneumoniae lower respiratory tract infection model, JNJ-Q2 displayed activity (ED50, 1.9 mg/kg administered s.c. and 7.4 mg/kg administered p.o.) that was comparable to that of gemifloxacin and superior to that of moxifloxacin. In both MRSA skin infection models, treatment with JNJ-Q2 resulted in dose-dependent reductions in bacterial titers in the skin, with the response to JNJ-Q2 at each dose exceeding the responses of the comparators ciprofloxacin, moxifloxacin, linezolid, and vancomycin. Additionally, in the ESI model, JNJ-Q2 showed a low or nondetectable propensity for ciprofloxacin resistance selection, in contrast to the selection of ciprofloxacin-resistant mutants observed for both ciprofloxacin and moxifloxacin. JNJ-Q2 demonstrated activity that was comparable or superior to the activity of fluoroquinolone or antistaphylococcal comparators in several local and systemic skin infection models performed with both S. aureus and S. pneumoniae and is currently being evaluated in phase II human clinical trials.
PMCID: PMC3232747  PMID: 21911568
5.  Pharmacokinetics of Dihydroartemisinin and Piperaquine in Pregnant and Nonpregnant Women with Uncomplicated Falciparum Malaria▿† 
Antimicrobial Agents and Chemotherapy  2011;55(12):5500-5506.
Dihydroartemisinin-piperaquine is a fixed-dose artemisinin-based combination treatment. Some antimalarials have altered pharmacokinetics in pregnancy. Pregnant women in the 2nd or 3rd trimester and matched nonpregnant women with uncomplicated falciparum malaria were treated with a total of 6.4 mg/kg of body weight dihydroartemisinin and 51.2 mg/kg piperaquine once daily for 3 days. Venous blood samples were drawn at prespecified time points over 9 weeks. Plasma dihydroartemisinin and piperaquine concentrations were analyzed by liquid chromatography-mass spectrometry. Piperaquine and dihydroartemisinin pharmacokinetics were well described. There were no significant differences in total piperaquine exposure (P = 0.80) or drug exposure during the terminal elimination phase (72 h to infinity) (P = 0.64) between the two groups. The apparent volume of distribution of piperaquine was significantly smaller (602 liters/kg versus 877 liters/kg) in pregnant women than in nonpregnant women (P = 0.0057), and the terminal elimination half-life was significantly shorter (17.8 days versus 25.6 days; P = 0.0023). Dihydroartemisinin exposure after the first dose was significantly lower (844 h × ng/ml versus 1,220 h × ng/ml, P = 0.0021) in pregnant women, but there were no significant differences in total dihydroartemisinin exposure or maximum concentrations between the two groups. There were no significant differences in any pharmacokinetic parameters between the second and third trimester. These results obtained through noncompartmental analysis suggest that in the treatment of falciparum malaria, there are no clinically important differences in the pharmacokinetics of dihydroartemisinin or piperaquine between pregnant and nonpregnant women. However, a more detailed analysis using population pharmacokinetic modeling is needed to fully investigate the differences found for some of the pharmacokinetic parameters, such as the terminal half-life.
PMCID: PMC3232755  PMID: 21947392
6.  Concentration of Antifungal Agents within Host Cell Membranes: a New Paradigm Governing the Efficacy of Prophylaxis ▿ † 
Antimicrobial Agents and Chemotherapy  2011;55(12):5732-5739.
Posaconazole prophylaxis has proven highly effective in preventing invasive fungal infections, despite relatively low serum concentrations. However, high tissue levels of this agent have been reported in treated patients. We therefore hypothesized that the intracellular levels of antifungal agents are an important factor in determining the success of fungal prophylaxis. To examine the effect of host cell-associated antifungals on the growth of medically important molds, we exposed cells to antifungal agents and removed the extracellular drug prior to infection. Epithelial cells loaded with posaconazole and its parent molecule itraconazole, but not other antifungals, were able to inhibit fungal growth for at least 48 h and were protected from damage caused by infection. Cell-associated posaconazole levels were 40- to 50-fold higher than extracellular levels, and the drug was predominantly detected in cellular membranes. Fungistatic levels of posaconazole persisted within epithelial cells for up to 48 h. Therefore, the concentration of posaconazole in mammalian host cell membranes mediates its efficacy in prophylactic regimens and likely explains the observed discrepancy between serum antifungal levels and efficacy.
PMCID: PMC3232766  PMID: 21930891
7.  Proposal of a Pharmacokinetically Optimized Dosage Regimen of Antibiotics in Patients Receiving Continuous Hemodiafiltration ▿ ‖ 
Antimicrobial Agents and Chemotherapy  2011;55(12):5804-5812.
The aim of the study was to quantitatively predict the clearance of three antibiotics, amikacin, vancomycin, and teicoplanin, during continuous hemodiafiltration (CHDF) and to propose their optimal dosage in patients receiving CHDF. For this goal, in vitro CHDF experiments with a polyacrylonitrile (PAN) membrane were first performed using these antibiotics, and then the clearances were compared with in vivo CHDF situations determined in 16 critically ill patients. The in vitro CHDF clearances were described as the product of the outflow rate of a drain (Qoutflow) and the drug unbound fraction in artificial plasma, indicating that drug adsorption to the PAN membrane has minor effect on drug clearance in our settings. The observed in vivo clearances also agreed very well with the predicted values, with a product of Qoutflow and plasma unbound fraction, when residual creatinine clearance (CLCR) was taken into account (within a range of 0.67- to 1.5-fold for 15 of 16 patients). Based on these results, a nomogram of the optimized dosages of amikacin, vancomycin, and teicoplanin was proposed, and it was evident that Qoutflow and residual CLCR are major determinants of the dosage and dosing interval for these antibiotics. Although the applicability needs to be confirmed with another type of membrane or higher Qoutflow, our nomogram can help determine the dosage setting in critically ill patients receiving CHDF.
PMCID: PMC3232773  PMID: 21911561
8.  Antistaphylococcal Activities of the New Fluoroquinolone JNJ-Q2▿§ 
Antimicrobial Agents and Chemotherapy  2011;55(12):5512-5521.
The new broad-spectrum fluoroquinolone JNJ-Q2 displays in vitro activity against Gram-negative and Gram-positive organisms, including methicillin-resistant Staphylococcus aureus (MRSA) and ciprofloxacin-resistant MRSA isolates. Tested with isogenic methicillin-susceptible S. aureus (MSSA) and MRSA strains bearing quinolone-resistant target mutations, JNJ-Q2 displayed MICs ≤ 0.12 μg/ml, values 16- to 32-fold lower than those determined for moxifloxacin. Overexpression of the NorA efflux pump did not impact JNJ-Q2 MICs. Inhibition of S. aureus DNA gyrase and DNA topoisomerase IV enzymes demonstrated that JNJ-Q2 was more potent than comparators against wild-type enzymes and enzymes carrying quinolone-resistant amino acid substitutions, and JNJ-Q2 displayed equipotent activity against both enzymes. In serial-passage studies comparing resistance selection in parallel MRSA cultures by ciprofloxacin and JNJ-Q2, ciprofloxacin readily selected for mutants displaying MIC values of 128 to 512 μg/ml, which were observed within 18 to 24 days of passage. In contrast, cultures passaged in the presence of JNJ-Q2 displayed MICs ≤ 1 μg/ml for a minimum of 27 days of serial passage. A mutant displaying a JNJ-Q2 MIC of 4 μg/ml was not observed until after 33 days of passage. Mutant characterization revealed that ciprofloxacin-passaged cultures with MICs of 256 to 512 μg/ml carried only 2 or 3 quinolone resistance-determining region (QRDR) mutations. Cultures passaged with JNJ-Q2 selection for up to 51 days displayed MICs of 1 to 64 μg/ml and carried between 4 and 9 target mutations. Established in vitro biofilms of wild-type or ciprofloxacin-resistant MRSA exposed to JNJ-Q2 displayed greater decreases in bacterial counts (7 days of exposure produced 4.5 to >7 log10 CFU decreases) than biofilms exposed to ciprofloxacin, moxifloxacin, rifampin, or vancomycin.
PMCID: PMC3232800  PMID: 21911562
9.  Randomized, Double-Blind, Phase II, Multicenter Study Evaluating the Safety/Tolerability and Efficacy of JNJ-Q2, a Novel Fluoroquinolone, Compared with Linezolid for Treatment of Acute Bacterial Skin and Skin Structure Infection ▿ † 
Antimicrobial Agents and Chemotherapy  2011;55(12):5790-5797.
JNJ-Q2 is a fluoroquinolone with broad coverage including methicillin-resistant Staphylococcus aureus (MRSA). A double-blind, multicenter, phase II noninferiority study treated 161 patients for 7 to 14 days, testing the efficacy of JNJ-Q2 (250 mg, twice a day [BID]) versus linezolid (600 mg, BID) in patients with acute bacterial skin and skin structure infections (ABSSSI). The prespecified criterion for noninferiority was 15%. Primary intent-to-treat analysis was unable to declare noninferiority, as the risk difference lower bound of the 95% confidence interval between treatments was 19% at 36 to 84 h postrandomization for the composite end point of lesion assessment and temperature. Prespecified clinical cure rates 2 to 14 days after completion of therapy were similar (83.1% for JNJ-Q2 versus 82.1% for linezolid). Post hoc analyses revealed that JNJ-Q2 was statistically noninferior to linezolid (61.4% versus 57.7%, respectively; P = 0.024) based on the 2010 FDA guidance, which defines treatment success as lack of lesion spread and afebrile status within 48 to 72 h postrandomization. Despite evidence of systemic disease, <5% of patients presented with fever, suggesting fever is not a compelling surrogate measure of systemic disease resolution for this indication. Nausea and vomiting were the most common adverse events. Of the patients, 86% (104/121) had S. aureus isolated from the infection site; 63% of these were MRSA. The results suggest JNJ-Q2 shows promise as an effective treatment for ABSSSI, demonstrating (i) efficacy for early clinical response (i.e., lack of spread of lesions and absence of fever at 48 to 72 h), and (ii) cure rates for ABSSSI pathogens (especially MRSA) consistent with the historical literature.
PMCID: PMC3232810  PMID: 21947389
10.  Correlation of Susceptibility of Cryptococcus neoformans to Amphotericin B with Clinical Outcome ▿ †  
Antimicrobial Agents and Chemotherapy  2011;55(12):5624-5630.
Testing of Cryptococcus neoformans for susceptibility to antifungal drugs by standard microtiter methods has not been shown to correlate with clinical outcomes. This report describes a modified quantitative broth macrodilution susceptibility method showing a correlation with both the patient's quantitative biological response in the cerebrospinal fluid (CSF) and the survival of 85 patients treated with amphotericin B (AMB). The Spearman rank correlation between the quantitative in vitro measure of susceptibility and the quantitative measure of the number of organisms in the patient's CSF was 0.37 (P < 0.01; 95% confidence interval [95% CI], 0.20, 0.60) for the first susceptibility test replicate and 0.46 (P < 0.001; 95% CI, 0.21, 0.62) for the second susceptibility test replicate. The median in vitro estimated response (defined as the fungal burden after AMB treatment) at 1.5 mg/liter AMB for patients alive at day 14 was 5 CFU (95% CI, 3, 8), compared to 57 CFU (95% CI, 4, 832) for those who died before day 14. These exploratory results suggest that patients whose isolates show a quantitative in vitro susceptibility response below 10 CFU/ml were more likely to survive beyond day 14.
PMCID: PMC3232814  PMID: 21947402
11.  The Antibacterial Activity of Ga3+ Is Influenced by Ligand Complexation as Well as the Bacterial Carbon Source ▿ † ‡ 
Antimicrobial Agents and Chemotherapy  2011;55(12):5568-5580.
Gallium ions have previously been shown to exhibit antibacterial and antibiofilm properties. In this study, we report differential bactericidal activities of two gallium complexes, gallium desferrioxamine B (Ga-DFOB) and gallium citrate (Ga-Cit). Modeling of gallium speciation in growth medium showed that DFOB and citrate both can prevent precipitation of Ga(OH)3, but some precipitation can occur above pH 7 with citrate. Despite this, Ga-Cit 90% inhibitory concentrations (IC90) were lower than those of Ga-DFOB for clinical isolates of Pseudomonas aeruginosa and several reference strains of other bacterial species. Treatment with Ga compounds mitigated damage inflicted on murine J774 macrophage-like cells infected with P. aeruginosa PAO1. Again, Ga-Cit showed more potent mitigation than did Ga-DFOB. Ga was also taken up more efficiently by P. aeruginosa in the form of Ga-Cit than in the form of Ga-DFOB. Neither Ga-Cit nor Ga-DFOB was toxic to several human cell lines tested, and no proinflammatory activity was detected in human lung epithelial cells after exposure in vitro. Metabolomic analysis was used to delineate the effects of Ga-Cit on the bacterial cell. Exposure to Ga resulted in lower concentrations of glutamate, a key metabolite for P. aeruginosa, and of many amino acids, indicating that Ga affects various biosynthesis pathways. An altered protein expression profile in the presence of Ga-Cit suggested that some compensatory mechanisms were activated in the bacterium. Furthermore, the antibacterial effect of Ga was shown to vary depending on the carbon source, which has importance in the context of medical applications of gallium.
PMCID: PMC3232821  PMID: 21947396
12.  Phase III Randomized, Double-Blind Study Comparing Single-Dose Intravenous Peramivir with Oral Oseltamivir in Patients with Seasonal Influenza Virus Infection ▿ † 
Antimicrobial Agents and Chemotherapy  2011;55(11):5267-5276.
Antiviral medications with activity against influenza viruses are important in controlling influenza. We compared intravenous peramivir, a potent neuraminidase inhibitor, with oseltamivir in patients with seasonal influenza virus infection. In a multinational, multicenter, double-blind, double-dummy randomized controlled study, patients aged ≥20 years with influenza A or B virus infection were randomly assigned to receive either a single intravenous infusion of peramivir (300 or 600 mg) or oral administration of oseltamivir (75 mg twice a day [b.i.d.] for 5 days). To demonstrate the noninferiority of peramivir in reducing the time to alleviation of influenza symptoms with hazard model analysis and a noninferiority margin of 0.170, we planned to recruit 1,050 patients in South Korea, Japan, and Taiwan. A total of 1,091 patients (364 receiving 300 mg and 362 receiving 600 mg of peramivir; 365 receiving oseltamivir) were included in the intent-to-treat infected population. The median durations of influenza symptoms were 78.0, 81.0, and 81.8 h in the groups treated with 300 mg of peramivir, 600 mg of peramivir, and oseltamivir, respectively. The hazard ratios of the 300- and 600-mg-peramivir groups compared to the oseltamivir group were 0.946 (97.5% confidence interval [CI], 0.793, 1.129) and 0.970 (97.5% CI, 0.814, 1.157), respectively. Both peramivir groups were noninferior to the oseltamivir group (97.5% CI, <1.170). The overall incidence of adverse drug reactions was significantly lower in the 300-mg-peramivir group, but the incidence of severe reactions in either peramivir group was not different from that in the oseltamivir group. Thus, a single intravenous dose of peramivir may be an alternative to a 5-day oral dose of oseltamivir for patients with seasonal influenza virus infection.
PMCID: PMC3195028  PMID: 21825298
13.  Pyrazinoic Acid Decreases the Proton Motive Force, Respiratory ATP Synthesis Activity, and Cellular ATP Levels▿† 
Antimicrobial Agents and Chemotherapy  2011;55(11):5354-5357.
Pyrazinoic acid, the active form of the first-line antituberculosis drug pyrazinamide, decreased the proton motive force and respiratory ATP synthesis rates in subcellular mycobacterial membrane assays. Pyrazinoic acid also significantly lowered cellular ATP levels in Mycobacterium bovis BCG. These results indicate that the predominant mechanism of killing by this drug may operate by depletion of cellular ATP reserves.
PMCID: PMC3195041  PMID: 21876062
14.  Excretion of Moxidectin into Breast Milk and Pharmacokinetics in Healthy Lactating Women ▿ † 
Antimicrobial Agents and Chemotherapy  2011;55(11):5200-5204.
Moxidectin, registered worldwide as a veterinary antiparasitic agent, is currently under development for humans for the treatment of onchocerciasis in collaboration with the World Health Organization. The objective of this study was to assess the pharmacokinetics of moxidectin in healthy lactating women, including the excretion into breast milk. Twelve women, ages 23 to 38 years, weighing 54 to 79 kg, all more than 5 months postpartum, were enrolled, following their plan to wean their infants and provision of informed consent. A single 8-mg, open-label dose was administered orally after consumption of a standard breakfast. Complete milk collection was done for approximately 28 days, and plasma samples were collected for 90 days. Moxidectin concentrations were measured by high-performance liquid chromatography (HPLC) with fluorescence detection, with a validated range of 0.08 to 120 ng/ml. Noncompartmental pharmacokinetic methods were used to find the following results: peak concentration in plasma (Cmax), 87 ± 25 ng/ml; time to Cmax (tmax), 4.18 ± 1.59 h; terminal-phase elimination half-life (t1/2), 832 ± 321 h; total area under the concentration-time curve (AUC), 4,046 ± 1,796 ng·h/ml; apparent oral dose clearance (CL/F), 2.35 ± 1.07 l/h; ratio of CL/F to the terminal-phase disposition rate constant, λz (Vλz/F), 2,526 ± 772 liters; percentage of maternal dose excreted in milk, 0.701 ± 0.299%; absolute amount excreted in milk, 0.056 ± 0.024 mg; relative infant dose, 8.73 ± 3.17% of maternal dose assuming complete absorption; clearance in milk (CLmilk), 0.016 ± 0.009 liter/h. Nine of 12 subjects reported adverse events, all of which were considered treatment emergent but not drug related and were mostly reported during the long outpatient period 8 to 90 days after dose administration. The most frequently reported adverse events were headache and nausea (n = 4), oropharyngeal pain (n = 2), rhinitis, viral pharyngitis, and viral upper respiratory tract infection (n = 2).
PMCID: PMC3195050  PMID: 21896908
15.  Survey of Antimicrobial Resistance in Clinical Burkholderia pseudomallei Isolates over Two Decades in Northeast Thailand ▿ † 
Antimicrobial Agents and Chemotherapy  2011;55(11):5388-5391.
A 21-year survey conducted in northeast Thailand of antimicrobial resistance to parenteral antimicrobial drugs used to treat melioidosis identified 24/4,021 (0.6%) patients with one or more isolates resistant to ceftazidime (n = 8), amoxicillin-clavulanic acid (n = 4), or both drugs (n = 12). Two cases were identified at admission, and the remainder were detected a median of 15 days after starting antimicrobial therapy. Resistance to carbapenem drugs was not detected. These findings support the current prescribing recommendations for melioidosis.
PMCID: PMC3195054  PMID: 21876049
16.  Genomewide Scan Reveals Amplification of mdr1 as a Common Denominator of Resistance to Mefloquine, Lumefantrine, and Artemisinin in Plasmodium chabaudi Malaria Parasites▿†‡ 
Antimicrobial Agents and Chemotherapy  2011;55(10):4858-4865.
Multidrug-resistant Plasmodium falciparum malaria parasites pose a threat to effective drug control, even to artemisinin-based combination therapies (ACTs). Here we used linkage group selection and Solexa whole-genome resequencing to investigate the genetic basis of resistance to component drugs of ACTs. Using the rodent malaria parasite P. chabaudi, we analyzed the uncloned progeny of a genetic backcross between the mefloquine-, lumefantrine-, and artemisinin-resistant mutant AS-15MF and a genetically distinct sensitive clone, AJ, following drug treatment. Genomewide scans of selection showed that parasites surviving each drug treatment bore a duplication of a segment of chromosome 12 (translocated to chromosome 04) present in AS-15MF. Whole-genome resequencing identified the size of the duplicated segment and its position on chromosome 4. The duplicated fragment extends for ∼393 kbp and contains over 100 genes, including mdr1, encoding the multidrug resistance P-glycoprotein homologue 1. We therefore show that resistance to chemically distinct components of ACTs is mediated by the same genetic mutation, highlighting a possible limitation of these therapies.
PMCID: PMC3186966  PMID: 21709099
17.  Prediction of Failure in Vancomycin-Treated Methicillin-Resistant Staphylococcus aureus Bloodstream Infection: a Clinically Useful Risk Stratification Tool▿† 
Antimicrobial Agents and Chemotherapy  2011;55(10):4581-4588.
Methicillin-resistant Staphylococcus aureus (MRSA) is a common cause of bloodstream infection (BSI) and is often associated with invasive infections and high rates of mortality. Vancomycin has remained the mainstay of therapy for serious Gram-positive infections, particularly MRSA BSI; however, therapeutic failures with vancomycin have been increasingly reported. We conducted a comprehensive evaluation of the factors (patient, strain, infection, and treatment) involved in the etiology and management of MRSA BSI to create a risk stratification tool for clinicians. This study included consecutive patients with MRSA BSI treated with vancomycin over 2 years in an inner-city hospital in Detroit, MI. Classification and regression tree analysis (CART) was used to develop a risk prediction model that characterized vancomycin-treated patients at high risk of clinical failure. Of all factors, the Acute Physiology and Chronic Health Evaluation II (APACHE-II) score, with a cutoff point of 14, was found to be the strongest predictor of failure and was used to split the population into two groups. Forty-seven percent of the population had an APACHE-II score < 14, a value that was associated with low rates of clinical failure (11%) and mortality (4%). Fifty-four percent of the population had an APACHE-II score ≥ 14, which was associated with high rates of clinical failure (35%) and mortality (23%). The risk stratification model identified the interplay of three other predictors of failure, including the vancomycin MIC as determined by Vitek 2 analysis, the risk level of the source of BSI, and the USA300 strain type. This model can be a useful tool for clinicians to predict the likelihood of success or failure in vancomycin-treated patients with MRSA bloodstream infection.
PMCID: PMC3186992  PMID: 21825294
18.  Adjunctive Rifampin Is Crucial to Optimizing Daptomycin Efficacy against Rabbit Prosthetic Joint Infection Due to Methicillin-Resistant Staphylococcus aureus▿† 
Antimicrobial Agents and Chemotherapy  2011;55(10):4589-4593.
Daptomycin is an attractive option for treating prosthetic joint infection, but the 6-mg/kg of body weight/day dose was linked to clinical failure and emergence of resistance. Using a methicillin-resistant Staphylococcus aureus (MRSA) knee prosthesis infection in rabbits, we studied the efficacies of high-dose daptomycin (22 mg/kg given intravenously [i.v.] once daily [o.d.]; equivalent to 8 mg/kg/day in humans) or vancomycin (60 mg/kg given intramuscularly [i.m.] twice daily [b.i.d.]), both either alone or with adjunctive rifampin (10 mg/kg i.m. b.i.d.). After partial knee replacement with a silicone implant, 107 MRSA CFU was injected into the knees. Treatment started 7 days postinoculation and lasted 7 days. Positive cultures were screened for the emergence of mutant strains, defined as having 3-fold-increased MICs. Although in vivo mean log10 CFU/g of daptomycin-treated (4.23 ± 1.44; n = 12) or vancomycin-treated (4.63 ± 1.08; n = 12) crushed bone was significantly lower than that of controls (5.93 ± 1.15; n = 9) (P < 0.01), neither treatment sterilized bone (2/12 and 0/12 rabbits with sterile bone, respectively). Daptomycin mutant strains were found in 6/12, 3/12, and 2/9 daptomycin-treated, vancomycin-treated, and control rabbits, respectively; no resistant strains emerged (MIC was always <1 mg/liter). Adjunctive rifampin with daptomycin (1.47 ± 0.04 CFU/g of bone [detection threshold]; 11/11 sterile bones) or vancomycin (1.5 ± 0.12 CFU/g of bone; 6/8 sterile bones) was significantly more effective than monotherapy (P < 0.01) and prevented the emergence of daptomycin mutant strains. In this MRSA joint prosthesis infection model, combining rifampin with daptomycin was highly effective. Daptomycin mutant strains were isolated in vivo even without treatment, but adjunctive rifampin prevented this phenomenon, previously found after monotherapy in humans.
PMCID: PMC3186998  PMID: 21825285
19.  Dolutegravir (S/GSK1349572) Exhibits Significantly Slower Dissociation than Raltegravir and Elvitegravir from Wild-Type and Integrase Inhibitor-Resistant HIV-1 Integrase-DNA Complexes▿† 
Antimicrobial Agents and Chemotherapy  2011;55(10):4552-4559.
The integrase inhibitor (INI) dolutegravir (DTG; S/GSK1349572) has significant activity against HIV-1 isolates with raltegravir (RAL)- and elvitegravir (ELV)-associated resistance mutations. As an initial step in characterizing the different resistance profiles of DTG, RAL, and ELV, we determined the dissociation rates of these INIs with integrase (IN)-DNA complexes containing a broad panel of IN proteins, including IN substitutions corresponding to signature RAL and ELV resistance mutations. DTG dissociates slowly from a wild-type IN-DNA complex at 37°C with an off-rate of 2.7 × 10−6 s−1 and a dissociative half-life (t1/2) of 71 h, significantly longer than the half-lives for RAL (8.8 h) and ELV (2.7 h). Prolonged binding (t1/2, at least 5 h) was observed for DTG with IN-DNA complexes containing E92, Y143, Q148, and N155 substitutions. The addition of a second substitution to either Q148 or N155 typically resulted in an increase in the off-rate compared to that with the single substitution. For all of the IN substitutions tested, the off-rate of DTG from IN-DNA complexes was significantly slower (from 5 to 40 times slower) than the off-rate of RAL or ELV. These data are consistent with the potential for DTG to have a higher genetic barrier to resistance, provide evidence that the INI off-rate may be an important component of the mechanism of INI resistance, and suggest that the slow dissociation of DTG may contribute to its distinctive resistance profile.
PMCID: PMC3187001  PMID: 21807982
20.  Mutation of RNA Polymerase β Subunit (rpoB) Promotes hVISA-to-VISA Phenotypic Conversion of Strain Mu3▿† 
The clinical vancomycin-intermediate Staphylococcus aureus (VISA) strain Mu50 carries two mutations in the vraSR and graRS two-component regulatory systems (TCRSs), namely, vraS(I5N) and graR(N197S) (hereinafter designated graR*). The clinical heterogeneously vancomycin-intermediate S. aureus (hVISA) strain Mu3 shares with Mu50 the mutation in vraS that encodes the VraS two-component histidine kinase. Previously, we showed that introduction of the plasmid pgraR*, carrying the mutated two-component response regulator graR*, converted the hVISA strain Mu3 into VISA (vancomycin MIC = 4 mg/liter). Subsequently, however, we found that the introduction of a single copy of graR* into the Mu3 chromosome by a gene replacement method did not confer on Mu3 the VISA phenotype. The gene-replaced strain Mu3graR* thus obtained remained hVISA (MIC ≤ 2 mg/liter), although a small increase in vancomycin MIC was observed compared to that of the parent strain Mu3. Reevaluation of the Mu3 and Mu50 genomes revealed the presence of another mutation responsible for the expression of the VISA phenotype in Mu50. Here, we demonstrate that in addition to the two regulator mutations, a third mutation found in the Mu50 rpoB gene, encoding the RNA polymerase β subunit, was required for Mu3 to achieve the level of vancomycin resistance of Mu50. The selection of strain Mu3graR* with rifampin gave rise to rpoB mutants with various levels of increased vancomycin resistance. Furthermore, 3 (33%) of 10 independently isolated VISA strains established from the heterogeneous subpopulations of Mu3graR* were found to possess rpoB mutations with or without an accompanying rifampin-resistance phenotype. The data indicate that a sizable proportion of the resistant hVISA cell subpopulations is composed of spontaneous rpoB mutants with various degrees of increased vancomycin resistance.
PMCID: PMC3165293  PMID: 21746940
21.  Lack of an Effect of Standard and Supratherapeutic Doses of Linezolid on QTc Interval Prolongation▿† 
A double-blind, placebo-controlled, four-way crossover study was conducted in 40 subjects to assess the effect of linezolid on corrected QT (QTc) interval prolongation. Time-matched, placebo-corrected QT intervals were determined predose and at 0.5, 1 (end of infusion), 2, 4, 8, 12, and 24 h after intravenous dosing of linezolid 600 and 1,200 mg. Oral moxifloxacin at 400 mg was used as an active control. The pharmacokinetic profile of linezolid was also evaluated. At each time point, the upper bound of the 90% confidence interval (CI) for placebo-corrected QTcF values (i.e., QTc values adjusted for ventricular rate using the correction methods of Fridericia) for linezolid 600 and 1,200-mg doses were <10 ms, which indicates an absence of clinically significant QTc prolongation. At 2 and 4 h after the moxifloxacin dose, corresponding to the population Tmax, the lower bound of the two-sided 90% CI for QTcF when comparing moxifloxacin to placebo was >5 ms, indicating that the study was adequately sensitive to assess QTc prolongation. The pharmacokinetic profile of linezolid at 600 mg was consistent with previous observations. Systemic exposure to linezolid increased in a slightly more than dose-proportional manner at supratherapeutic doses, but the degree of nonlinearity was small. At a supratherapeutic single dose of 1,200 mg of linezolid, no treatment-related increase in adverse events was seen compared to 600 mg of linezolid, and no clinically meaningful effects on vital signs and safety laboratory evaluations were noted.
PMCID: PMC3165302  PMID: 21709083
22.  A Small Amount of Fat Does Not Affect Piperaquine Exposure in Patients with Malaria▿† 
Dihydroartemisinin-piperaquine is a new, highly effective, and well-tolerated combination treatment for uncomplicated falciparum malaria. The lipophilic characteristic of piperaquine suggests that administration together with fat will increase the oral bioavailability of the drug, and this has been reported for healthy volunteers. This pharmacokinetic study monitored 30 adult patients with uncomplicated falciparum malaria for 4.5 months to evaluate the effects of the concomitant intake of fat on the total piperaquine exposure. The fixed-drug combination of dihydroartemisinin-piperaquine was given with water to fasting patients (n = 15) or was coadministered with 200 ml milk containing 6.4 g fat (n = 15). The drug combination was generally well tolerated, and there were no severe adverse effects reported for either group during the study. Total piperaquine exposure (area under the concentration-time curve from zero to infinity [AUC0-∞]; results are given as medians [ranges]) were not statistically different between fed (29.5 h · μg/ml [20.6 to 58.7 h · μg/ml]) and fasting (23.9 h · μg/ml [11.9 to 72.9 h · μg/ml]) patients, but the interindividual variation was reduced in the fed group. Overall, none of the pharmacokinetic parameters differed statistically between the groups. Total piperaquine exposure correlated well with the day 7 concentrations in the fasted group, but the fed group showed a poor correlation. In conclusion, the coadministration of 6.4 g fat did not have any significant effect on piperaquine pharmacokinetics in the treatment of uncomplicated malaria.
PMCID: PMC3165307  PMID: 21709087
23.  Pharmacokinetics of Amodiaquine and Desethylamodiaquine in Pregnant and Postpartum Women with Plasmodium vivax Malaria▿† 
In order to study the pharmacokinetic properties of amodiaquine and desethylamodiaquine during pregnancy, 24 pregnant women in the second and third trimesters of pregnancy and with Plasmodium vivax malaria were treated with amodiaquine (10 mg/kg of body weight/day) for 3 days. The same women were studied again at 3 months postpartum. Plasma was analyzed for amodiaquine and desethylamodiaquine by use of a liquid chromatography-tandem mass spectrometry method. Individual concentration-time data were evaluated using noncompartmental analysis. There were no clinically relevant differences in the pharmacokinetics of amodiaquine and desethylamodiaquine between pregnant (n = 24) and postpartum (n = 18) women. The results suggest that the current amodiaquine dosing regimen is adequate for the treatment of P. vivax infections during pregnancy.
PMCID: PMC3165320  PMID: 21709098
24.  An Open-Label Crossover Study To Evaluate Potential Pharmacokinetic Interactions between Oral Oseltamivir and Intravenous Zanamivir in Healthy Thai Adults▿† 
There is no parenteral formulation of the neuraminidase inhibitor oseltamivir, the most widely used anti-influenza virus drug. Oseltamivir resistance is an increasing problem. Zanamivir is effective against the most prevalent oseltamivir-resistant influenza viruses. A parenteral formulation of zanamivir is in development for the treatment of severe influenza. It is not known if there is any pharmacokinetic interaction between the two drugs. Sixteen healthy Thai adult volunteers were studied in an open-label, four-period, randomized two-sequence crossover pharmacokinetic study in which zanamivir was given by constant-rate infusion or slow intravenous injection either alone or together with oral oseltamivir. Plasma concentration profiles of oseltamivir, the active metabolite oseltamivir carboxylate, and zanamivir were measured by liquid chromatography-mass spectrometry-mass spectrometry. Both drugs were well tolerated alone and in combination. The maximum plasma concentrations and the areas under the plasma concentration-time curves (AUC) of oseltamivir and oseltamivir carboxylate were not significantly different when oseltamivir was given separately or together with zanamivir. Maximum plasma concentrations of zanamivir were 10% (95% confidence interval, 7 to 12%) higher when zanamivir was infused concurrently with oral oseltamivir than with infusions before or after oral oseltamivir. The plasma zanamivir total AUC was positively correlated with the total oseltamivir carboxylate AUC (Pearson's correlation coefficient [rP] = 0.720, P = 0.002, n = 16) but not with the oseltamivir AUC (rp = 0.121, n = 16). There is no clinically significant pharmacokinetic interaction between oseltamivir and zanamivir.
PMCID: PMC3165358  PMID: 21690287
25.  LEADER Program Results for 2009: an Activity and Spectrum Analysis of Linezolid Using 6,414 Clinical Isolates from 56 Medical Centers in the United States▿† 
The LEADER Program monitors the in vitro activity of linezolid in sampled U.S. medical centers using reference broth microdilution methods with supporting molecular investigations in a central laboratory design. This report summarizes data obtained in 2009, the 6th consecutive year of this longitudinal study. A total of 6,414 isolates from 56 medical centers in all nine Census regions across the United States participated in 2009. For the six leading species/groups, the following linezolid MIC90 values were observed: Staphylococcus aureus, 2 μg/ml; coagulase-negative staphylococci (CoNS), 1 μg/ml; Enterococcus spp., 2 μg/ml; Streptococcus pneumoniae, 1 μg/ml; viridans group streptococci, 1 μg/ml; and beta-hemolytic streptococci, 1 μg/ml. Linezolid resistance was only 0.34% overall, with no evidence of significant increase in the LEADER Program since 2006. The predominant linezolid resistant mechanism found was a G2576T mutation in the 23S rRNA. L3/L4 riboprotein mutations were also found. The mobile multidrug-resistant cfr gene was found in four strains (two S. aureus strains and one strain each of S. epidermidis and S. capitis) from four different states, suggesting persistence but a lack of dissemination. Linezolid continues to exhibit excellent activity and spectrum, and this study documents the need for continued monitoring of emerging mechanisms of resistance over a wide geographic area.
PMCID: PMC3147616  PMID: 21670176

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