Therapeutic drug monitoring of nevirapine in resource-limited settings.

BACKGROUND: We developed a simple and inexpensive thin-layer chromatography (TLC) assay for semiquantitative detection of saliva concentrations of nevirapine in resource-limited settings. The method was validated in an African target population. METHODS: Paired plasma and saliva nevirapine concentrations were assayed by high-performance liquid chromatography (HPLC); saliva concentrations of nevirapine were also assayed by TLC. The rate of false-positive results was the proportion of subtherapeutic nevirapine saliva and plasma concentrations determined by HPLC that were judged to be therapeutic in saliva specimens by TLC. The rate of false-negative results was the proportion of therapeutic nevirapine saliva and plasma concentrations determined by HPLC that were judged to be subtherapeutic in saliva specimens by TLC. The extent of agreement in TLC readings between 5 technicians and 2 batches of TLC sheets was evaluated. RESULTS: Twenty-five (9%) of 286 African adults had a subtherapeutic plasma nevirapine concentration. The median ratio of nevirapine concentrations in saliva to those in plasma was 0.51:1. The rate of false-positive results for TLC was 0% (0 of 23 specimens) when TLC results were compared with HPLC results for saliva specimens and 8% (2 of 25 specimens) when TLC results were compared with HPLC results for plasma specimens. The rate of false-negative results for TLC was 1% (3 of 263 specimens) when TLC results were compared with HPLC results for saliva specimens and 1% (3 of 261 specimens) when TLC results were compared with HPLC results for plasma specimens. The extent of agreement of TLC results was substantial for the 5 technicians (Fleiss's kappa = 0.77) and for the 2 batches of sheets (Cohen's kappa = 0.80). CONCLUSIONS: The TLC assay was found to be sensitive, specific, and robust in the detection of subtherapeutic nevirapine concentrations in saliva specimens obtained from African HIV-infected adults. It is an attractive alternative to HPLC for therapeutic drug monitoring of nevirapine in resource-limited settings.

Semen quality and drug concentrations in seminal plasma of patients using a didanosine or didanosine plus tenofovir containing antiretroviral regimen.

Data on the concentrations of didanosine (ddI) and tenofovir (TFV) in seminal plasma are sparse. Subtherapeutic drug concentrations within the lumen of the male genital tract may have implications for selection and transmission of drug-resistant HIV strains. On the other hand, sufficient penetration of these drugs into the male genital tract has potential toxic effects on the spermatozoa and their precursors. In the current study, the authors obtained paired semen and blood samples at variable time points after drug intake from 30 HIV-1-infected patients using a ddI (n = 15) or ddI + TFV (n = 15) containing an antiretroviral regimen. Didanosine and TFV concentrations were measured in seminal and blood plasma and semen quality was assessed. Both ddI and TFV penetrated well into seminal plasma. Whereas blood plasma ddI concentrations dropped to near or below the lower limit of quantification of 0.017 microg/mL 9 hours after drug intake, the ddI concentration in seminal plasma remained detectable during the whole dosing interval with a median of 0.20 and 0.21 microg/mL in the ddI and ddI + TFV groups, respectively. Tenofovir was detectable during the whole dosing interval in both blood and seminal plasma with a median concentration of 0.12 and 0.25 microg/mL, respectively, and a median seminal-to-blood-plasma ratio of 3.3. Semen quality was within the normal range according to the criteria of the World Health Organization, except for the percentage of progressively motile sperm, which was low in both groups of patients. The authors conclude that ddI and TFV penetrate well into seminal plasma and that the reduced sperm motility deserves further study.

Assessment of drug-drug interactions between tenofovir disoproxil fumarate and the nonnucleoside reverse transcriptase inhibitors nevirapine and efavirenz in HIV-infected patients.

BACKGROUND: Tenofovir disoproxil fumarate (DF) has been studied in combination with efavirenz in healthy volunteers and no interaction was found. No data are available on the possible interaction of tenofovir DF with nevirapine and efavirenz in HIV-infected patients. In this study the combination of nevirapine 200 mg twice daily with tenofovir DF 300 mg once daily and nevirapine 400 mg once daily with tenofovir DF 300 mg once daily were compared with nevirapine twice daily or once daily without tenofovir DF in HIV-infected patients. Furthermore, the combination of efavirenz 600 mg and tenofovir DF 300 mg once daily was compared with use of efavirenz 600 mg once daily only. METHODS: Data were retrospectively collected from routine therapeutic drug monitoring plasma samples. Nevirapine, efavirenz, and tenofovir plasma levels and tenofovir concentration ratios were analyzed. The concentration ratio represents the measured plasma concentration compared with the time-adjusted average concentration, as measured in a reference population. Six different groups were studied: 200 mg nevirapine twice daily, 400 mg nevirapine once daily, 600 mg efavirenz once daily, all without tenofovir DF (groups 1, 2, and 3, respectively), and the same groups with the drugs combined with tenofovir 300 mg once daily (groups 4, 5, and 6, respectively). RESULTS: Plasma samples were evaluable for 272, 18, 126, 32, 94, and 118 patients in the groups 1-6, respectively. No differences were found in plasma levels for tenofovir, nevirapine, and efavirenz for either of the combinations studied. Addition of tenofovir DF to efavirenz or nevirapine in HIV-infected patients does not influence the plasma levels of nevirapine or efavirenz. Furthermore, nevirapine and efavirenz have no effect on tenofovir plasma levels or tenofovir concentration ratios. CONCLUSION: Efavirenz or nevirapine can be coadministered with tenofovir DF in HIV-infected patients without dose modifications.

No virological failure in semen during properly suppressive antiretroviral therapy despite subtherapeutic local drug concentrations.

PURPOSE: The aim of the study was to investigate whether drug resistance occurs earlier in seminal than in blood plasma with the use of such HAART regimens, of which only the two NRTIs achieve therapeutic concentrations in seminal plasma. METHOD: Seminal and blood plasma of 12 patients, for 48-96 weeks on suppressive first-line therapy with saquinavir/ritonavir/didanosine/lamivudine, nelfinavir/didanosine/stavudine, or efavirenz/lamivudine/zidovudine were prospectively evaluated for HIV-1-RNA resistance mutations and drug concentrations. RESULTS: Saquinavir, nelfinavir, and efavirenz blood plasma concentrations were in the therapeutic range. Nelfinavir and efavirenz seminal plasma concentrations were below the limit of quantification. In only 2 of 9 seminal plasma samples, from 1 of 6 patients, the saquinavir concentration was above the minimum therapeutic level. The seminal plasma HIV-1-RNA concentration remained undetectable in all patients up to 96 weeks, and therefore drug resistance could not be demonstrated. Thus, despite suboptimal local drug concentrations, no virological failure occurred in seminal plasma after prolonged first-line HAART. CONCLUSION: This finding supports the hypothesis that the source of HIV in semen is a spillover from the blood/extraluminal tissue and that therefore seminal plasma drug levels may not be critical for viral suppression within the lumen of the male genital tract.

TDM: therapeutic drug measuring or therapeutic drug monitoring?

The third round of the International Interlaboratory Quality Control Program for Therapeutic Drug Monitoring in HIV infection (QC-program) consisted of the analysis not only of plasma samples but also of patient cases. The case was composed of different topics related to the therapeutic drug monitoring of antiretroviral drugs. The participants were asked to give recommendations concerning dose adjustments, changes to the regimen, and drug-drug interactions to observe whether the expert recommendations were comparable. Of the 30 participants of the QC-program, 16 returned their comments and recommendations with regard to the patient case. The drug level was easy to judge: approximately 90% were able to correctly do so. Almost half of the recommendations (44%) given were satisfactory. Levels of knowledge regarding HIV treatment appeared to be variable among the respondents and for this reason were partly incomparable.

Nevirapine plasma concentrations are still detectable after more than 2 weeks in the majority of women receiving single-dose nevirapine: implications for intervention studies.

BACKGROUND: Single-dose nevirapine is a highly cost-effective strategy to reduce perinatal HIV-1 transmission. Its major disadvantage is the selection of nevirapine resistance in 20% to 30% of women, probably attributable to the long elimination half-life of nevirapine. To develop intervention strategies, it is important to know the interpatient variability in nevirapine half-life in women receiving a single dose of nevirapine. METHODS: HIV-negative, healthy, nonpregnant Dutch women were eligible for this study. After administration of a single 200-mg dose of nevirapine to the subjects, blood was sampled for measurement of nevirapine twice a week for a total of 21 days. Nevirapine plasma levels were determined by a validated high-performance liquid chromatography method with a lower limit of quantification of 0.15 mg/L. The primary end point was the first sample with an undetectable nevirapine concentration. RESULTS: Forty-four subjects participated. The median age, height, and body weight (interquartile range) were 26 (21-33) years, 1.72 (1.68-1.75) m, and 64 (59-75) kg, respectively. The median elimination half-life of nevirapine was 56.7 hours, with a range of 25.6 to 164 hours. The time to the first undetectable nevirapine plasma concentration was 10 days in 4 subjects, 14 days in 12 subjects, 17 days in 12 subjects, and 21 days in 9 subjects. In the remaining 7 subjects, nevirapine was still detectable on day 21, the last day of sampling. Time to an undetectable nevirapine plasma concentration was influenced by oral contraceptive use but not by age, height, body weight, body surface area, alcohol use, or smoking. CONCLUSIONS: Most women who received a single 200-mg nevirapine dose still had detectable plasma concentrations of nevirapine after more than 2 weeks. This information is valuable for designing intervention studies to prevent the development of nevirapine resistance.

Evaluation of antiretroviral drug measurements by an interlaboratory quality control program.

Since 1999 an ongoing international interlaboratory quality control program has analyzed antiretroviral drugs in plasma. Results of the third round of this program are presented. Quality control samples were prepared by spiking drug-free plasma with varying concentrations of the currently available protease inhibitors and the nonnucleoside reverse transcriptase inhibitors efavirenz and nevirapine. Thirty-three laboratories participated in the program and were requested to analyze the quality control samples. Results were from 30 laboratories. Of all measurements, 82% were performed within 80%-120% accuracy limits. Only 3 laboratories performed all their measurements within these limits, and 12 participants reported at least 90% of their analyses within the acceptance range. Mean accuracy for low drug concentrations was worse than for medium and high concentrations. The percentage of satisfactory measurements for the 6 laboratories that participated for the third time in the program increased from 54% in the first round to 85% in the third round. The program revealed a large variability in the laboratories' ability to measure antiretroviral drugs accurately. This variability may have important implications for therapeutic drug monitoring of these drugs and for pharmacokinetic studies. Interlaboratory testing is useful to alert laboratories to previously undetected analytical problems.