Nevirapine Concentrations Research Articles

Evaluation of Saliva as an Alternative Matrix for Monitoring Plasma Zidovudine, Lamivudine and Nevirapine Concentrations in Rwanda

Saliva may provide interesting advantages as matrix for compliance measurements, pharmacokinetic studies and therapeutic drug monitoring in resource limited countries. We investigated the feasibility of using saliva for compliance monitoring of zidovudine (ZDV), lamivudine (3TC) and nevirapine (NVP) in 29 HIV-1 infected patients from Rwanda. ZDV, 3TC and NVP drug levels were quantified by an LC/MS-MS method in plasma and stimulated saliva samples and compared using Bland-Altman analysis. Seven patients demonstrated undetectable saliva ZDV levels while five out of these seven also showed no 3TC salivary concentrations. For the other samples, we observed a good agreement between salivary and plasma concentrations of each antiretroviral drug. A significant relation between the difference in saliva and plasma ZDV concentrations and the average ZDV concentration in the two matrices was deduced as follow: y = -380.15 + 1.79 x. The log saliva and plasma concentration difference of both 3TC and NVP was consistent across the range of average log concentration. Overall, we showed large agreement limits suggesting a wide inter patient variability that may result to non-reliable plasma level predictions from saliva drug measurements. Therefore, our results indicate that saliva may serve as a valuable tool only for NVP compliance testing because of its high salivary concentration.

Good performance of an immunoassay based method for nevirapine measurements in human breast milk

Understanding the distribution of antiretro-virals in breastfeeding HIV-positive mothers is essential, both for prevention of mother-to-child HIV transmission and for research on the development of drug resistance. The ARK nevirapine (NVP)-test is an immunoassay method for nevirapine measurements, developed and validated for plasma use. In this study, the ARK NVP-test was evaluated for measurement of nevirapine concentrations in breast milk. High performance liquid chromatography (HPLC) is the method currently used to determine nevirapine in breast milk. This method, however, requires complicated extraction techniques. The ARK method employs an immunoassay technology and requires a small sample volume (40 μL) and no pre-treatment of the samples. Commercial enzyme and antibody were used and calibration standards and quality controls were prepared from pooled breast milk from HIV-uninfected women. Clinical samples from HIV-infected women receiving a single-dose of nevirapine were analyzed. Precision and accuracy were evaluated with two concentrations of quality control materials analyzed in three replicates on four different days and was <4%, and between 96.5% and 104.6%, respectively. Clinical samples were analyzed and CVs ranged from 0.0% to 11.1%. The median nevirapine concentration in breast milk 1 week post-partum was 0.29 μg/mL (range 0.11-0.90 μg/mL) in women treated with a single-dose of nevirapine. The ease of use and small sample volume makes the ARK assay an attractive alternative to HPLC analyses for determinations of nevirapine concentrations in breast milk.

Integration of population pharmacokinetics and pharmacogenetics: an aid to optimal nevirapine dose selection in HIV-infected individuals.

BackgroundNevirapine is metabolized by CYP2B6 and polymorphisms within the CYP2B6 gene partly explain inter-patient variability in pharmacokinetics. The aim of this study was to model the complex relationship between nevirapine exposure, weight and genetics (based on combined analysis of CYP2B6 516G > T and 983T > C single nucleotide polymorphisms).MethodsNon-linear mixed-effects modelling was used to estimate pharmacokinetic parameters from 275 patients. Simulations of the nevirapine concentration profile were performed with dosing regimens of 200 mg twice daily and 400 mg once daily for individuals with body weights of 50, 70 and 90 kg in combination with CYP2B6 genetic variation.ResultsA one-compartment model with first-order absorption best described the data. Population clearance was 3.5 L/h with inter-patient variability of 24.6%. 516T homozygosity and 983C heterozygosity were associated with 37% and 40% lower clearance, respectively. Body weight was the only significant demographic factor influencing clearance, which increased by 5% for every 10 kg increase. For individuals with higher body weight, once-daily nevirapine was associated with a greater risk of sub-therapeutic drug exposure than a twice-daily regimen. This risk was offset in individuals who were 516T homozygous or 983C heterozygous in which drug exposure was optimal for > 95% of patients with body weight of ≤70 kg.ConclusionsThe data suggest that a 400 mg once-daily dose could be implemented in accordance with CYP2B6 polymorphism and body weight. However, the use of nevirapine once daily (immediate release; off-label) in the absence of therapeutic drug monitoring is not recommended due to the risk of inadequate exposure to nevirapine in a high proportion of patients. There are different considerations for the extended-release formulation (nevirapine XR) that demonstrate minimal peak-to-trough fluctuations in plasma nevirapine levels.

Serum nevirapine and efavirenz concentrations and effect of concomitant rifampicin in HIV infected children on antiretroviral therapy

To determine factors affecting serum levels of Efavirenz and Nevirapine and analyze the effect of Rifampicin on Nevirapine drug levels. A cross-sectional study was conducted on 30 HIV infected children on Antiretroviral therapy (ART) with Nevirapine or Efavirenz. Patients on simultaneous Rifampicin and Nevirapine were given higher doses of Nevirapine with regular monitoring of liver function tests. Trough levels (before morning dose of Nevirapine) and levels after 2 hours of administration of Nevirapine and levels of Efavirenz were assessed using HPLC and were checked to see if they fall within the therapeutic range. Thirty patients (14 males) were enrolled in the study with 20 on Nevirapine and 10 (33.3%) on Efavirenz. Seven (23.3%) patients were simultaneously taking rifampicin. The mean Nevirapine dose given to the patients was 350.9±59.8 mg/m2/day (on simultaneous rifampicin) and 309.2±54.6 mg/m2/day (not on concurrent rifampicin). Thirteen (81.3%) of the 16 patients with trough Nevirapine had values in the normal range, 1 (6.3%) had low Nevirapine trough levels and 2 (12.5%) had high Nevirapine trough levels. Of the post 2 hours Nevirapine levels, 1 (5%) had low levels and 3 (15%) had high Nevirapine blood levels. Factors like age (P=0.4, P=0.4087), nourishment (P=0.2679, P=0.4132), ART combination (P=0.4199, P=0.4132), form of the drug (tablet/syrup) (P=0.1964, P=0.4696) or if it was being given as single or in a fixed dose combination (P=0.4179, P=0.4696) and even concurrent rifampicin administration (P=0.284, P=0.472) did not significantly affect the trough and post 2 hours Nevirapine values, respectively. All the five patients being given concurrent rifampicin had normal trough and post 2 hours levels of Nevirapine. The Efavirenz drug levels were 1.9±1.1 g/mL. Of the 10 patients on Efavirenz, 2 (20%) had high and 1 (10%) had low blood levels. Concurrent Rifampicin administration does not alter blood levels of Nevirapine; provided the dose of Nevirapine is increased by 20-30%. Formulation of drugs does not alter the blood levels provided drug administered is in the recommended dose.

Factors influencing plasma nevirapine levels: a study in HIV-infected children on generic antiretroviral treatment in India

Nevirapine is an important component of paediatric combination HIV therapy. Adequate drug exposure is necessary in order to achieve long-lasting viral suppression. To study the influence of age, drug dose and formulation type, nutritional status and CYP2B6 516G>T polymorphism on blood concentrations of nevirapine in children treated with generic antiretroviral drugs. A multicentre study was conducted at four sites in India. HIV-infected children receiving generic nevirapine-based fixed-dose combinations were recruited. Trough and 2 h nevirapine plasma concentrations were determined by HPLC. Characterization of the CYP2B6 gene polymorphism was performed using direct sequencing. Clinical and nutritional status was recorded. Groups were compared using the Mann-Whitney U-test and multivariable logistic regression analysis was performed to identify factors contributing to low drug levels. Ninety-four children of median age 78 months were studied; 60% were undernourished or stunted. Stunted children had a significantly lower 2 h nevirapine concentration compared with non-stunted children (P < 0.05); there were no significant differences in trough concentrations between different nutritional groups. Nevirapine levels were significantly higher in children with TT compared with GG and GT CYP2B6 genotypes (P < 0.01). Children ≤ 3 years had a 3.2 (95% confidence interval 1.07-9.45) times higher risk of having sub-therapeutic nevirapine concentrations. Nevirapine blood concentrations are affected by many factors, most notably age ≤ 3 years; a combination of young age, stunting and CYP2B6 GG or GT genotype could potentially result in sub-therapeutic nevirapine concentrations. Dosing recommendations for children should be reviewed in the light of these findings.

“Forgiving” a Missed Daily Dose

Editor: adherence is an essential component of a successful drug regimen.1 Simplification of a therapeutic regimen with once-daily treatment options is an important strategy to improve or sustain adherence to treatment. An extended release 400 mg tablet formulation of the nonnucleoside reverse transcriptase inhibitor nevirapine has been developed2 to offer the potential benefit of once-daily highly active antiretroviral therapy (HAART) to HIV-1-positive patients. The double-blind 48-week VERxVE trial with a total of over 1000 patients confirmed the noninferior virologic efficacy of the nevirapine 400 mg extended release once-daily regimen as compared to the standard immediate release 200 mg twice-daily regimen of nevirapine. The extended release formulation also demonstrated minimal peak-to-trough fluctuations in plasma nevirapine levels.3 As a result of metabolic enzyme autoinduction following a month of oral therapy, the half-life of nevirapine (200 mg twice daily) stabilizes at approximately 24 h. Simplification to a once-daily regimen was the objective in developing an extended release formulation. This was achieved by delaying the release of the total nevirapine dose at a slower rate over a 24-h period. Systemic absorption is prolonged for an additional day, thereby minimizing the fluctuations in the peak-to-trough concentrations of the active drug. As long as there is drug in the intestinal tract,4 this smoothing of the circulating drug concentrations leads to a longer timeframe at which the drug is at therapeutic concentrations, thereby minimizing the impact of a single missed dose of extended release nevirapine. Minimizing the impact of a single missed dose is important for a nonnucleoside reverse transcriptase inhibitor (NNRTI) such as nevirapine, as adherence rates of less than 95% have been associated with inadequate long-term treatment outcome.5 In the 2NN study,6 one treatment arm consisting of 208 patients on immediate release nevirapine 400 mg once daily had a median Cmax concentration of 7.88 μg/ml and a trough concentration of 3.26 μg/ml, resulting in a peak-to-trough ratio slightly greater than 2, consistent with dosing based on the half-life of the drug. In the VERxVE trial,3 with 418 patients on nevirapine extended release 400 mg once daily, the trough concentration of 3.50 μg/ml was maintained. However, the estimate of Cmax in a subset of patients was only 3.77 μg/ml, resulting in a peak-to-trough ratio approaching 1, consistent with extended first-order release and absorption matching the elimination rate of the drug. To illustrate the relative impact of a single missed daily dose of nevirapine, data from 2NN (two immediate release tablets for a total of 400 mg) and data from VERxVE (a single 400 mg extended release tablet) were modeled at steady state (4 weeks after treatment initiation), along with a simulation of expected nevirapine concentrations if the next dose was missed (Fig. 1). As illustrated in Fig. 1, trough nevirapine concentrations 48 h after the last dose are 2.1 μg/ml (88 × EC50 of 90 nM) for the extended release dosage form, but only 1.3 μg/ml (54 × EC50) for an immediate release 400 mg (2 × 200 mg tablets) dose taken once daily in an off-label manner. The extended release formulation maintains a 60% greater plasma concentration of nevirapine, a “forgiveness” difference that may be clinically significant for some patients on HAART therapy. Medication adherence to the entire HAART regimen must still be emphasized to the patient in order to avoid functional monotherapy and because consistent missed doses (more than once in 2 weeks) will lower overall systemic nevirapine levels irrespective of “forgiveness.” Consecutively missing more than one day of therapy may require reinitiation of a HAART loading regimen to obtain proper therapeutic levels of each drug and to prevent selection of resistance. FIG. 1. Modeled nevirapine concentration time curves for 2NN and VERxVE trials over a 24-h steady-state interval (troughs of 3.4 μg/ml at 0 and 24 h, respectively) and simulated curves for a missed dose at 24 h (troughs of 2.1 ...

Automatic Nevirapine concentration interpretation system using support vector regression

Follow-up of human immunodeficiency virus (HIV) patients treated with Nevirapine (NVP) is a necessary process to evaluate the drug resistance and the HIV mutation. It is also usually tested by immunochromatographic (IC) strip test. However, it is difficult to estimate the amount of drug the patient gets by visually inspection of color. In this paper, we propose an automatic interpretation system using a commercialized optical scanner. Several IC strips can be placed at any direction as long as they are on the scanner plate. There are three steps in the system, i.e., light intensity normalization, image segmentation and NVP concentration interpretation. We utilized the Support Vector Regression to interpret the NVP concentration. From the results, we found out the performance of the system is promising and better than that of the linear and nonlinear regression.

Intracellular Concentrations of Non-Nucleoside Reverse Transcriptase Inhibitors and its Potential Role on Apoptosis in Peripheral Blood Mononuclear Cells

Background: Efavirenz (EFV) and nevirapine (NVP) are non-nucleoside reverse transcriptase inhibitors (NNRTIs) that are frequently used in combination with other antiretrovirals for the treatment of HIV-infected persons. Little information is available regarding the intracellular concentrations (ICs) of EFV and NVP in peripheral blood mononuclear cells (PBMCs) and its potential role for cellular toxicity. Methods: PBMCs from healthy adult donors were treated with or without the mean peak steady-state levels (Cmax) of EFV (12.4µM) and NVP (17.0µM) in human plasma during antiretroviral therapy multiplied by 0.5, 1.0, 2.0 and 4.0. After 48 hr treatment, ICs of EFV and NVP were measured using liquid chromatoagraphy-ion trap/mass spectrometry. The degree of apoptotic cells and mitochondrial membrane potential in PBMCs were measured by flow cytometry. Results: The mean log ICs of x1.0 Cmax NVP in PBMCs (2.00 ± 0.23 µM) were significantly lower than the one of x1.0 Cmax EFV (2.95 ± 0.22 µM) (P < 0.01). Similar significant differences of mean log ICs were observed when the concentration of NNRTIs were x0.5 Cmax (1.62 ± 0.26 µM vs. 2.87 ± 0.13 µM, P < 0.01) and x2.0 Cmax (1.99 ± 0.39 µM vs. 3.11 ± 0.21 µM, P < 0.01). Furthermore, apoptotic PBMCs were lower than PBMC treated with the concentrations of NVP above the plasma Cmax observed clinically in patients as compared to those treated with comparable concentrations of EFV (P < 0.01). Conclusion: These in vitro data suggest that ICs of NVP in PBMCs are significantly lower than ICs of EFV in PBMC and are also associated with less apoptotic PBMCs. The clinical relevance of this observation remains to be elucidated.

The antiretroviral efficacy of highly active antiretroviral therapy and plasma nevirapine concentrations in HIV-TB co-infected Indian patients receiving rifampicin based antituberculosis treatment

BackgroundRifampicin reduces the plasma concentrations of nevirapine in human immunodeficiency virus (HIV) and tuberculosis (TB) co-infected patients, who are administered these drugs concomitantly. We conducted a prospective interventional study to assess the efficacy of nevirapine-containing highly active antiretroviral treatment (HAART) when co-administered with rifampicin-containing antituberculosis treatment (ATT) and also measured plasma nevirapine concentrations in patients receiving such a nevirapine-containing HAART regimen.Methods63 cases included antiretroviral treatment naïve HIV-TB co-infected patients with CD4 counts less than 200 cells/mm3 started on rifampicin-containing ATT followed by nevirapine-containing HAART. In control group we included 51 HIV patients without tuberculosis and on nevirapine-containing HAART. They were assessed for clinical and immunological response at the end of 24 and 48 weeks. Plasma nevirapine concentrations were measured at days 14, 28, 42 and 180 of starting HAART.Results97 out of 114 (85.1%) patients were alive at the end of 48 weeks. The CD4 cell count showed a mean increase of 108 vs.113 cells/mm3 (p=0.83) at 24 weeks of HAART in cases and controls respectively. Overall, 58.73% patients in cases had viral loads of less than 400 copies/ml at the end of 48 weeks. The mean (± SD) Nevirapine concentrations of cases and control at 14, 28, 42 and 180 days were 2.19 ± 1.49 vs. 3.27 ± 4.95 (p = 0.10), 2.78 ± 1.60 vs. 3.67 ± 3.59 (p = 0.08), 3.06 ± 3.32 vs. 4.04 ± 2.55 (p = 0.10) respectively and 3.04 μg/ml (in cases).ConclusionsGood immunological and clinical response can be obtained in HIV-TB co-infected patients receiving rifampicin and nevirapine concomitantly despite somewhat lower nevirapine trough concentrations. This suggests that rifampicin-containing ATT may be co administered in resource limited setting with nevirapine-containing HAART regimen without substantial reduction in antiretroviral effectiveness. Larger sample sized studies and longer follow-up are required to identify populations of individuals where the reduction in nevirapine concentration may result in lower ART response or shorter response duration.

Relative bioavailability of two formulations of nevirapine 200-mg tablets in healthy Chinese male volunteers: A single-dose, randomized-sequence, open-label, two-way crossover study

Background: Nevirapine was the first member of the nonnucleoside reverse transcriptase inhibitor class to be approved for the treatment of HIV infection. It binds directly to the allosteric site on the reverse transcriptase and inhibits the activity of both RNA- and DNA-dependent DNA polymerases. Objective: This study compared the pharmacokinetics and relative bioavailability of a test and reference formulation of nevirapine 200-mg tablets after single oral doses in healthy Chinese men to meet regulatory criteria for marketing of the new generic formulation. Methods: This single-dose, randomized-sequence, open-label, 2-way crossover study was conducted at the Nanjing First Hospital of Nanjing Medical University, Nanjing, China. Healthy male Chinese volunteers were randomized in a 1∶1 ratio to receive a single 200-mg (3.2-mg/kg) tablet of the test or reference formulation, followed by a 2-week washout period and administration of the alternate formulation. The study drugs were administered after a 10-hour overnight fast. Concentrations of nevirapine were assayed using an HPLC-UV method. For analysis of nevirapine pharmacokinetic parameters, blood samples were obtained before dosing and at regularly scheduled intervals over 168 hours after administration. The 2 formulations would be assumed to be bioequivalent for regulatory purposes if the 90% CIs for the log-transformed ratios of nevirapine AUC and C max were within the range established by the US Food and Drug Administration (0.80–1.25). Tolerability was evaluated throughout the study based on vital signs, physical examinations, 12-lead ECGs, and subject interviews concerning adverse events (AEs). Results: Twenty Chinese male subjects were enrolled in and completed the study. Their mean age was 23 years (range, 21–25 years), mean weight was 63 kg (range, 56–70 kg), and mean height was 171 cm (range, 166–176 cm). No period or sequence effect was observed. The mean (SD) t ½ was 38.12 (2.23) hours for the test tablet and 36.79 (5.06) hours for the reference tablet; T max was 3.1 (0.7) and 3.0 (0.7) hours, respectively; C max was 2.52 (0.31) and 2.60 (0.48) mg · L −1; AUC 0–168 was 155.66 (22.41) and 150.66 (22.11) mg · h · L −1; and AUC 0–∞ was 163.30 (22.88) and 157.75 (22.87) mg · h · L −1. Mean relative bioavailability was 103.6% (8.6%). The 90% CIs for the log-transformed ratios of C max (93.51–102.13) and AUC 0–168 ( 99.84–106.74) were within the predetermined range for the assumption of bioequivalence. One subject reported mild headache after receiving the test formulation; the relationship of this AE to study drug was considered uncertain. No serious or clinically significant AEs were observed or reported during the study. Conclusions: In this single-dose study in healthy fasted Chinese males, the test tablet met the regulatory criterion for assumption of bioequivalence to the reference tablet. Both formulations were well tolerated in the population studied. SFDA registration no: 2009L04358.

Nevirapine pharmacokinetics when initiated at 200 mg or 400 mg daily in HIV-1 and tuberculosis co-infected Ugandan adults on rifampicin

rifampicin lowers nevirapine plasma concentrations by inducing cytochrome P450. However, few data are available on this interaction during the lead-in period of nevirapine treatment. eighteen HIV-1/tuberculosis co-infected adults receiving rifampicin daily as part of anti-tuberculosis therapy were evenly randomized to nevirapine initiation by dose escalation (NVP200) or nevirapine initiation at 200 mg twice daily (NVP400). Subjects underwent 12 h intensive pharmacokinetic sampling on Days 7, 14 and 21 of nevirapine treatment. A minimum effective concentration (MEC) of 3000 ng/mL was used to interpret nevirapine concentrations 12 h after dosing (C(12)). NCT00617643 (www.clinicaltrials.gov). day 7 geometric mean nevirapine C(12) [90% confidence interval (CI)] was 1504 (1127-2115) ng/mL and 3148 (2451-4687) ng/mL in the NVP200 and NVP400 arms, respectively (P < 0.01). Nevirapine C(12) on Days 14 and 21 was similar. On Day 21, nevirapine concentration in 64% of patients was below the MEC. On Day 7, geometric mean area under the curve (AUC(0-12)) was lower in the NVP200 arm, 25 223 (90% CI, 21 978-29 695) ng·h/mL versus 43 195 (35 607-57 035) ng·h/mL in the NVP400 arm (P < 0.01). Similarly, on Day 14, nevirapine AUC(0-12) was lower in the NVP200 arm 23 668 (18 253-32 218) ng·h/mL versus the NVP400 arm 44 918 (36 264-62 769) ng·h/mL (P = 0.03). in co-treated patients, nevirapine concentrations were below the MEC during initiation with dose escalation. Nevirapine initiation at the maintenance dose of 200 mg twice daily is preferred. Sub-therapeutic nevirapine concentrations were common at Day 21 with either regimen. Evaluation of higher nevirapine maintenance doses may be considered.

Suboptimal Nevirapine Steady-State Pharmacokinetics During Intrapartum Compared With Postpartum in HIV-1-Seropositive Ugandan Women

Conflicting data exist regarding the effect of pregnancy on steady-state nevirapine pharmacokinetics (PK), although steady-state nevirapine concentrations during pregnancy have never been characterized in sub-Saharan Africa. This was a longitudinal intensive PK study in Ugandan pregnant women receiving nevirapine-based antiretroviral therapy. Participants underwent intensive 12-hour PK sampling during the second trimester (T2; n = 4), third trimester (T3; n = 15) and 6 weeks postpartum (PP; n = 15). HIV-1 RNA was performed within 2 weeks of each visit. Nevirapine C12 above 3000 ng/mL was classified as optimal based on the suggested value for therapeutic drug monitoring. The pharmacokinetics of nevirapine were influenced by pregnancy, demonstrated by a 20% reduction in the maximum concentration, minimum concentration (C12), and area under the curve between T3 and PP visits (P = 0.001, P = 0.011 and P = 0.005, respectively). Ten subjects (66.7%) had C12 values <3000 ng/mL during T3. Of these participants, 7 partcipant's C12 concentrations increased to >3000 ng/mL during the PP visit. HIV-1 RNA were <1000 copies per milliliter at T3 and <400 copies per milliliter at PP in all patients. Nevirapine exposure was reduced in Ugandan women during their third trimester compared with the same women PP, however, HIV RNA remained <1000 copies per milliliter. The long-term impact of intermittent suboptimal nevirapine concentrations during pregnancy is unknown.

Population Pharmacokinetics of Nevirapine in HIV-1-Infected Pregnant Women and Their Neonates

The aim of the present study was to describe the nevirapine (NVP) pharmacokinetics (PK) in pregnant women and their neonates and to evaluate the transplacental drug transfer and administration scheme for the prevention of mother-to-child transmission. Thirty-eight HIV-1-infected pregnant women were administered one tablet of NVP (200 mg) and two tablets of tenofovir-emtricitabine (Truvada) at the initiation of labor. Children were given NVP syrup (2 mg/kg of body weight) as a single dose (sdNVP) on the first day of life. By pair, NVP concentrations were measured in 11 maternal, 1 cord blood, and 2 neonatal plasma samples and analyzed by a population approach. A one-compartment model was used for mothers and neonates; the absorption rate constants for mothers and neonates were 0.95 h(-1) (intersubject variability, 111%) and 0.39 h(-1), respectively; the apparent elimination clearances were 1.42 liter·h(-1) (intersubject variability, 22%) and 0.035 liter·h(-1), respectively; and apparent volumes of distribution were 87.3 liters (intersubject variability, 25%) and 5.65 liters, respectively. An effect compartment was linked to maternal circulation by mother-to-cord and cord-to-mother rate constants of 1.10 h(-1) and 1.43 h(-1), respectively. Placental transfer, expressed as the fetal-to-maternal area under the curve ratio, was 75%. Neonates had a very long half-lives (110 h) compared to adults. In the 38 mothers, the simulated median individual predicted time during which the NVP concentration remained above the half-maximal inhibitory concentration (IC(50)) was 13.2 days (range, 12 to 19.2 days). Thus, the administration of tenofovir-emtricitabine for at least 3 weeks after delivery should be considered to prevent the emergence of resistant viruses. The neonate must receive sdNVP immediately after birth when the infant is born less than 30 min after maternal drug intake to keep NVP concentrations above the IC(50).

CYP2B6 Polymorphism and Nonnucleoside Reverse Transcriptase Inhibitor Plasma Concentrations in Chinese HIV-Infected Patients

The purpose of this study was to investigate the frequency of CYP2B6 polymorphisms and their influence on plasma concentrations of efavirenz and nevirapine in HIV-infected Chinese patients. After written informed consent, 159 patients were enrolled at Shanghai Public Health Clinical Center. Genotyping for 516 G>T, 785 A>G, 983 T>C, and 1459 T>C polymorphisms in CYP2B6, together with CYP3A4 -392 A>G, CYP3A5 6986 A>G, and ABCB1 (2677 G>T/A, 3435 C>T), were performed. Plasma efavirenz and nevirapine concentrations of 120 patients at steady state were assessed by high-performance liquid chromatography-mass spectrometry. The minor allele frequency for CYP2B6 516 G>T, 785 A>G, 983 T>C, and 1459 T>C was 0.16, 0.24, 0, and 0, respectively; and 0.07, 0.32, 0.15, and 0.35 for CYP3A4 -392 A>G, CYP3A5 6986 A>G, ABCB1 2677 G>T/A, and ABCB1 3435 C>T, respectively. Univariate analysis indicated associations between 516 G>T (P < 0.01) with efavirenz but not nevirapine plasma concentrations. None of other genetic variants was associated with plasma efavirenz or nevirapine concentrations. Although CYP2B6 516 G>T was associated with high plasma efavirenz concentrations, such an association was not evident with nevirapine in this Chinese patient population. CYP3A4 -392 A>G, CYP3A5 6986 A>G, and ABCB1 (2677 G>T/A, 3435 C>T) had no significant impact on plasma efavirenz or nevirapine concentrations.

Hemodialysis Does Not Significantly Affect the Pharmacokinetics of Nevirapine in HIV-1-Infected Persons Requiring Hemodialysis: Results From ACTG A5177

When characterizing the pharmacokinetics of a therapeutic agent, a key goal is to maximize efficacy while minimizing risk. Because pharmacokinetics studies are difficult to do in populations with severe end organ damage, such as end-stage renal disease, dosing recommendations in these populations may be extrapolated from other data or may be missing. In patients receiving dialysis, the added complexity of clearance by the dialysis process, which depends on the degree to which medications are protein bound, must be taken into account. Nevirapine (NVP) is a commonly used non-nucleoside antiretroviral agent that has only minimal renal elimination. However, hemodialysis may represent a significant route of NVP elimination in patients with end stage renal disease due to its relatively low volume of distribution (1.2 L/kg), low molecular weight, and being only 60% bound to plasma proteins.1 In the one previously published case report of NVP use in a patient receiving hemodialysis,2 the area under the concentration time curve was substantially reduced during dialysis with a 46.5% extraction ratio. However, NVP was dosed at only 200 mg once daily in this patient. Therefore, we examined the potential effects of hemodialysis on the steady-state pharmacokinetics of NVP, in HIV-1-infected subjects with end-stage renal disease requiring hemodialysis, when given at the usual dosing strategy of 200 mg twice daily. ACTG A5177 was a prospective observational study to estimate the steady-state pharmacokinetic (PK) parameters of efavirenz, lopinavir/ritonavir and NVP in HIV-infected subjects requiring hemodialysis. The efavirenz and lopinavir/ritonavir results have been reported elsewhere.3 This letter summarizes the pharmacokinetic results observed in the 3 subjects accrued to the NVP arm.

Limited Sampling Models to Predict the Pharmacokinetics of Nevirapine, Stavudine, and Lamivudine in HIV-Infected Children Treated With Pediatric Fixed-Dose Combination Tablets

Full 12-hour pharmacokinetic profiles of nevirapine, stavudine, and lamivudine in HIV-infected children taking fixed-dose combination antiretroviral tablets have been reported previously by us. Further studies with these formulations could benefit from less-intensive pharmacokinetic sampling. Data from 65 African children were used to relate area under the plasma concentration versus time curve over 12 hours (AUC) to plasma concentrations of nevirapine, stavudine, or lamivudine at times t = 0, 1, 2, 4, 6, 8, and 12 hours after intake using linear regression. Limited sampling models were developed using leave-one-out crossvalidation. The predictive performance of each model was evaluated using the mean relative prediction error (mpe%) as an indicator of bias and the root mean squared relative prediction error (rmse%) as a measure of precision. A priori set criteria to accept a limited sampling model were: 95% confidence limit of the mpe% should include 0, rmse% less than 10%, a high correlation coefficient, and as few (convenient) samples as possible. Using only one sample did not lead to acceptable AUC predictions for stavudine or lamivudine, although the 6-hour sample was acceptable for nevirapine (mpe%: -0.8%, 95% confidence interval: -2.2 to +0.6); rmse%: 5.8%; r: 0.98). Using two samples, AUC predictions for stavudine and lamivudine improved considerably but did not meet the predefined acceptance criteria. Using three samples (1, 2, 6 hours), an accurate and precise limited sampling model for stavudine AUC (mpe%: -0.6%, 95% confidence interval: -2.2 to +1.0; rmse%: 6.5%; r: 0.98) and lamivudine AUC (mpe%: -0.3%, 95% confidence interval: -1.7 to +1.1; rmse%: 5.6%; r: 0.99) was found; this model was also highly accurate and precise for nevirapine AUC (mpe%: -0.2%, 95% confidence interval: -1.0 to +0.7; rmse%: 3.4%; r: 0.99). A limited sampling model using three time points (1, 2, 6 hours) can be used to predict nevirapine, stavudine, and lamivudine AUC accurately and precisely in HIV-infected African children.

Compatibility risks between drugs and herbal medicines or botanical supplements

Herbal supplements along with prescribed medicines raise concerns of therapeutic activity due to possible drug–herbal interactions. MDR gene products: P-gp, MRP and BCRP and metabolizing enzyme (cytochrome P450) together constitute a highly effective barrier for many orally absorbed drugs. Therapeutic agents and active herbal constituents are substrates, inhibitors and inducers of both P-gp and CYP3A4. Inhibition of P-gp by pure herbal constituents such as hypericin, kaempferol and quercetin or extract of St. John's wort resulted in higher absorption of ritonavir and erythromycin in vitro. Similarly, inhibition of CYP by hypericin, kaempferol and quercetin also caused a remarkable reduction in cortisol metabolism in vitro. Conversely, an enhanced expression of both CYP3A4 and MDR-1 mRNA in Caco-2 cells was observed after chronic exposure of hyperforin, kaempferol, quercetin and hypericin, kaempferol, quercetin, silibinin respectively. Chronic exposure (96h) of African herbal (Sutherlandia frutescens) extract (300μg/mL) resulted in elevation of both P-gp and CYP3A4 expressions in LS180V cells. Cellular accumulation of [3H]Digoxin, a model P-gp substrate was significantly reduced indicating higher efflux. These in vitro results were further confirmed in rats. Administration of Sutherlandia-extract for 4 days significantly affected pharmacokinetics of nevirapine – a CYP3A4 (CYP3A2) substrate. Plasma concentration of nevirapine was diminished by 51% (Cmax) and 45% (AUC0-inf) compared to controls. Similar pharmacokinetics of fexofenadine, a P-gp substrate was also observed. Plasma concentration of fexofenadine was declined by 49.7% (Cmax) and 34.5% (AUC0-inf) compared to controls. Hepatic CYP3A4 and P-gp mRNA levels were enhanced by 3-fold and 1.75-fold respectively. Intestinal CYP3A4 (2-fold) and P-gp expressions (3-fold) was also elevated. Such reduction of steady state plasma concentrations of nevirapine and fexofenadine after concomitant administration of Sutherlandia in rats suggests medicinal agents that are substrates for P-gp and/or CYP are likely to be potential candidates for drug–herbal interactions.

Nonnucleoside Reverse Transcriptase Inhibitor Concentrations During Treatment Interruptions and the Emergence of Resistance: A Substudy of the ISS-PART Trial

Emergence of resistance is one of the drawbacks associated with treatment interruptions (TI), especially when regimens include nonnucleoside reverse transcriptase inhibitors (NNRTIs), because of their long half-life. ISS-PART was a randomized trial comparing a continuous treatment arm with a TI arm in which 136 patients underwent five treatment interruptions, each followed by 3 months of therapy, over 2 years. To minimize the potential risk of developing resistance, patients on NNRTIs were requested, at each TI, to interrupt nevirapine (NVP) or efavirenz (EFV) 3 or 6 days before the other drugs, respectively. To determine if a difference in drug levels existed during TIs between patients with and without resistance we compared NNRTI concentrations in the 12 patients (6 on NVP and 6 on EFV) who developed NNRTI mutations during TIs with those of 20 patients (10 on NVP and 10 on EFV) who retained a wild-type virus. Genotypic resistance and drug concentrations were analyzed on plasma samples collected 15 days after each drug interruption. Overall, EFV was quantifiable in 28% (16/57) and NVP in 22.9% (14/61) of evaluable samples collected during TIs, with no difference between patients with and without mutations. Median EFV or NVP concentrations at each TI were not significantly different between patients with and without mutations. Although the staggered stop strategy was not completely effective in preventing exposure to suboptimal levels, no evident correlation was found between NNRTI concentrations and the emergence of resistance, suggesting that other factors (such as the presence of drug-resistant minority variants) could also play an important role in these patients.

Effects of CYP2B6 G516T polymorphisms on plasma efavirenz and nevirapine levels when co-administered with rifampicin in HIV/TB co-infected Thai adults

BackgroundCytochrome P450 2B6 (CYP2B6) metabolizes efavirenz and nevirapine, the major core antiretroviral drugs for HIV in Thailand. Rifampicin, a critical component of tuberculosis (TB) therapy is a potent inducer of CYP enzyme activity. Polymorphisms of CYP2B6 and CYP3A4 are associated with altered activity of hepatic enzyme in the liver and pharmacokinetics resulting in treatment efficacy. This study aimed to investigate whether CYP2B6 or CYP3A4 polymorphisms had effects on plasma efavirenz and nevirapine concentrations when co-administered with rifampicin in HIV/TB co-infected Thai adults.ResultsWe studied 124 rifampicin recipients with concurrent HIV-1/TB coinfection, receiving efavirenz (600 mg/day) (n = 65) or nevirapine (400 mg/day) (n = 59) based antiretroviral therapy (ART). The frequencies of GG, GT and TT genotypes of CYP2B6-G516T were 38.46%, 47.69% and 13.85% in efavirenz group and 44.07%, 52.54% and 3.39% in nevirapine group, respectively. The mean 12-hour post-dose plasma efavirenz concentration in patients with TT genotype at weeks 6 and 12 of ART and 1 month after rifampicin discontinuation (10.97 ± 2.32, 13.62 ± 4.21 and 8.48 ± 1.30 mg/L, respectively) were significantly higher than those with GT (3.43 ± 0.29, 3.35 ± 0.27 and 3.21 ± 0.22 mg/L, respectively) (p < 0.0001) or GG genotypes (2.88 ± 0.33, 2.45 ± 0.26 and 2.08 ± 0.16 mg/L, respectively) (p < 0.0001). Likewise, the mean 12-hour post-dose plasma nevirapine concentration in patients carrying TT genotype at weeks 6 and 12 of ART and 1 month after rifampicin discontinuation (14.09 ± 9.49, 7.94 ± 2.76 and 9.44 ± 0.17 mg/L, respectively) tended to be higher than those carrying GT (5.65 ± 0.54, 5.58 ± 0.48 and 7.03 ± 0.64 mg/L, respectively) or GG genotypes (5.42 ± 0.48, 5.34 ± 0.50 and 6.43 ± 0.64 mg/L, respectively) (p = 0.003, p = 0.409 and p = 0.448, respectively). Compared with the effects of CYP2B6-516TT genotype, we could observe only small effects of rifampicin on plasma efavirenz and nevirapine levels. After 12 weeks of both drug regimens, there was a trend towards higher percentage of patients with CYP2B6-TT genotype who achieved HIV-1 RNA levels <50 copies/mL compared to those with GT or GG genotypes. This is the first report to demonstrate the effects of CYP2B6 G516T polymorphisms on plasma efavirenz and nevirapine concentrations when co-administered with rifampicin in HIV/TB co-infected Thai adults.ConclusionsCYP2B6-TT genotype had impact on plasma efavirenz and nevirapine concentrations, while rifampicin co-administration had only small effects.

Emergence and persistence of nevirapine resistance in breast milk after single-dose nevirapine administration.

Single-dose nevirapine (NVP) (sdNVP) can reduce the risk of HIV vertical transmission. We assessed risk factors for NVP resistance in plasma and breast milk from sdNVP-exposed Ugandan women. Samples were analyzed using the Roche AMPLICOR HIV-1 Monitor Test Kit, version 1.5, and the ViroSeq HIV-1 Genotyping System. NVP concentrations were determined by liquid chromatography with tandem mass spectroscopy. HIV genotypes (plasma and breast milk) were obtained for 30 women 4 weeks after sdNVP (HIV subtypes: 15A, 1C, 12D, two recombinant). NVP resistance was detected in 12 (40%) of 30 breast milk samples. There was a nonsignificant trend between detection of NVP resistance in breast milk and plasma (P = 0.06). There was no association of HIV resistance in breast milk with median maternal pre-NVP viral load or CD4 cell count, median breast milk viral load at 4 weeks, breast milk sodium more than 10 mmol/l, HIV subtype, or concentration of NVP in breast milk or plasma. NVP resistance was frequently detected in breast milk 4 weeks after sdNVP exposure. In this study, we were unable to identify specific factors associated with breast milk NVP resistance.