Pharmacokinetic-pharmacodynamic determinants of oseltamivir efficacy using data from phase 2 inoculation studies.

Given the limited understanding about pharmacokinetic-pharmacodynamic (PK-PD) determinants of oseltamivir efficacy, data from two phase 2 influenza virus inoculation studies were evaluated. Healthy volunteers in studies 1 and 2 were experimentally infected with influenza A/Texas (the concentration of neuraminidase inhibitor which reduced neuraminidase activity by 50% [IC(50)] = 0.18 nM) or B/Yamagata (IC(50) = 16.76 nM), respectively. In study 1, 80 subjects received 20, 100, or 200 mg of oral oseltamivir twice daily (BID), 200 mg oseltamivir once daily, or placebo for 5 days. In study 2, 60 subjects received 75 or 150 mg of oral oseltamivir BID or placebo for 5 days. Oseltamivir carboxylate (OC) (active metabolite) PK was evaluated using individual PK data and a population PK model to derive individual values for area under the concentration-time curve from 0 to 24 h (AUC(0-24)), minimum concentration of OC in plasma (C(min)), and maximum concentration of OC in plasma (C(max)). Exposure-response relationships were evaluated for continuous (area under composite symptom score curve [AUCSC], area under the viral titer curve, and peak viral titer) and time-to-event (alleviation of composite symptom scores and cessation of viral shedding) efficacy endpoints. Univariable analyses suggested the existence of intuitive and highly statistically significant relationships between OC AUC(0-24 )evaluated as a 3-group variable and AUCSC, time to alleviation of composite symptom scores, and time to cessation of viral shedding. The upper OC AUC(0-24) threshold (~14,000 ng · h/ml) was similar among these endpoints. Multivariable analyses failed to demonstrate the influence of study/strain on efficacy endpoints. These results provide the first demonstration of exposure-response relationships for efficacy for oseltamivir against influenza and suggest that OC exposures beyond those achieved with the approved oseltamivir dosing regimen will provide enhanced efficacy. The clinical applicability of these observations requires further investigation.

Susceptibility profile of vaginal isolates of Candida albicans prior to and following fluconazole introduction - impact of two decades.

Current treatment options for vulvovaginal candidiasis due to Candida albicans include over-the-counter and prescription antifungal agents. Fluconazole has been used extensively with an unknown impact on susceptibility. To investigate antifungal susceptibility trends in clinical vaginal isolates of C. albicans from 1986 to 2008, microdilution susceptibility was performed on randomly selected single isolates. Minimum inhibitory concentrations (MICs) were determined for: fluconazole, clotrimazole, miconazole, ketoconazole, itraconazole, voriconazole, flucytosine and amphotericin B. The MIC(90) for each drug was then calculated for the time periods: 1986-1989, 1992-1996 and 2005-2007. A total of 250 C. albicans vaginal isolates were included. The MIC(90) (mcg ml(-1) ) for fluconazole was 0.25, 0.5 and 0.5 mcg ml(-1) for each grouping, respectively. The corresponding MIC(90) for flucytosine was 1, 2 and 8 mcg ml(-1) , respectively. The MIC(90) for the remaining agents remained unchanged across time periods mentioned. Of note, the percentage of isolates with MIC ≥1 and ≥2 mcg ml(-1) for fluconazole increased from 3% to 9% over the study period. Although the C. albicans MIC(90) to fluconazole in vaginal isolates has not shown a clinically significant increase since 1986, there is an increasing number of isolates with elevated MICs. The implications of this increase are unknown, but given the achievable vaginal concentrations of fluconazole, reduced susceptibility may have clinical relevance.