Tim R. Cressey

Efavirenz pharmacokinetics during the third trimester of pregnancy and postpartum.

Background: The impact of pregnancy on efavirenz (EFV) pharmacokinetics is unknown. Methods: International Maternal Pediatric Adolescent AIDS Clinical Trials P1026s is an on-going, prospective, nonblinded study of antiretroviral pharmacokinetics in HIV-infected pregnant women that included a cohort receiving 600 mg EFV once daily as part of combination antiretroviral therapy. Intensive steady-state 24-hour blood sampling was performed during the third trimester and at 6–12 weeks postpartum. Maternal and umbilical cord blood samples were drawn at delivery. Pharmacokinetics targets were the estimated 10th percentile EFV area under the curve (AUC) in nonpregnant historical controls (40.0 mcg·hr−1·mL−1) and a trough concentration of 1 mcg/mL. Results: Twenty-five women were enrolled during the third trimester: median (range) age was 29.3 (18.9–42.9) years, weight 69.0 (40–130) kg, and gestational age 32.9 (30.1–38.7) weeks. Median (range) EFV AUC0–24, Cmax, and C24 hours were 55.4 mcg·hr−1·mL−1 (13.5-220.3), 5.4 mcg/mL (1.9–12.2), and 1.6 mcg/mL (0.23–8.13), respectively. EFV AUC and Cmax did not differ during pregnancy and postpartum but C24 hours was lower during the third trimester (1.6 vs. 2.1 mcg/mL, P = 0.01). During the third trimester, 5 of 25 (20%) women had an EFV AUC below the target and 3 of 25 (12%) had a trough concentration below 1 mcg/mL. EFV cord blood/maternal concentration ratio was 0.49 (0.37–0.74). All women had a HIV-1 RNA viral load less than 400 copies per milliliter at delivery and 19 (76%) had a viral load below 50 copies per milliliter. One child was perinatally HIV infected. Three women were exposed to EFV throughout the first 6 weeks of pregnancy. EFV was well tolerated, and among the 25 infants, no congenital anomalies or newborn complications were reported. Conclusions: Changes in EFV pharmacokinetics during pregnancy compared with postpartum are not sufficiently large enough to warrant a dose adjustment during pregnancy.

Pharmacokinetics of nevirapine in HIV-infected children receiving an adult fixed-dose combination of stavudine, lamivudine and nevirapine

Objective:To evaluate the steady state pharmacokinetics of nevirapine (NVP) in HIV-infected children receiving a fixed-dose combination of stavudine, lamivudine and NVP. Methods:This cross-sectional study enrolled 34 children (18 girls) who had received GPO-VIR S30 (30 mg stavudine, 150 mg lamivudine and 200 mg NVP) for at least 8 weeks. Tablets were divided into quarter fractions (1/4, 1/2, 3/4 or 1 tablet) to attain the NVP dosages of 120–200 mg/m2 every 12 h. Plasma NVP levels were measured at predose, and at 2 and 6 h after drug administration. Results:The median age was 8.4 years (range, 3–15). Median CD4 lymphocyte count and percentage at study entry was 576 × 106 cells/l and 20.25%, respectively. The median pharmacokinetics parameters were area under the curve at 12 h, 78.4 h × μg/ml; minimum plasma drug concentration, 5.98 μg/ml; plasma half-life, 25.5 h; apparent oral clearance, 0.079 l/kg per h; and volume of distribution, 2.95 l/kg. Only one child had a minimum plasma drug concentration < 3.4 μg/ml (2.57 μg/ml). Of the 13 children who received GPO-VIR as their first-line regimen, 12 had plasma HIV-1 RNA < 400 copies/ml at 6–18 months, with a median CD4 lymphocyte increase of 216 and 433 × 106 cells/l at 6 and 12 months of treatment, respectively. Conclusions:The administration of GPO-VIR S30 fixed-dose combination tablets in fractions or as a whole tablet to children resulted in appropriate NVP exposure and satisfactory virological and immunological benefit. This finding confirms the effectiveness of using a fixed-dose combination as a ‘transitional option’ while waiting for a paediatric fixed-dose combination drug formulation.

Influence of CYP2B6 polymorphisms on the persistence of plasma nevirapine concentrations following a single intra-partum dose for the prevention of mother to child transmission in HIV-infected Thai women

OBJECTIVES To investigate the association of single nucleotide polymorphisms (SNPs) with nevirapine concentrations following intra-partum single-dose nevirapine. METHODS Plasma and DNA samples were obtained from 330 HIV-infected Thai women who received intra-partum single-dose nevirapine in the PHPT-2 clinical trial to prevent perinatal HIV transmission. Nine SNPs within CYP2B6, CYP3A4 and ABCB1 were genotyped by real-time PCR. Nevirapine plasma concentrations were determined by HPLC and used in a population pharmacokinetic analysis. RESULTS Higher nevirapine exposure was observed in women carrying the CYP2B6 516G>T polymorphism, but this did not reach statistical significance (P = 0.054). The TGATC CYP2B6 haplotype (g.3003T, 516G, 785A, g.18492T and g.21563C) was associated with increased nevirapine clearance and lower exposure (P = 0.0029). The median time for nevirapine concentrations to reach 10 ng/mL post-partum (nevirapine IC(50) for HIV-1) was 14 days [interquartile range (IQR, 14-18)] for TGATC homozygotes, 16 days (14-20) for TGATC heterozygotes and 18 days (14-20) for non-TGATC homozygotes (P = 0.020). CONCLUSIONS The CYP2B6 516G>T impact on nevirapine concentrations was less pronounced after intra-partum single-dose nevirapine than reported under steady-state conditions, perhaps due to lack of enzyme auto-induction at the time of dosing. Although the TGATC CYP2B6 haplotype may shorten the persistence of nevirapine post-partum, its practical implications for the prevention of HIV transmission or selection of resistance mutations are likely limited.

Predictors of 5-year mortality in HIV-infected adults starting highly active antiretroviral therapy in Thailand.

Objective:To estimate the early and long-term mortalities and associated risk factors in adults receiving highly active antiretroviral therapy (HAART) in Thailand. Design:A prospective observational cohort study. Methods:Previously untreated adults starting HAART in 2002–2009 were followed-up in 43 public hospitals. Kaplan–Meier probability of survival was estimated up to 5 years of therapy. Factors associated with early (⩽6 months) and long-term (>6 months) mortalities were assessed using Cox regression analyses. Results:A total of 1578 adults received HAART (74% women; median age, 33 years; CD4 cell count, 124/mL), with a median follow-up of 50 months (interquartile range, 41–66). Eighty-nine patients (6%) died (37 occurred ⩽6 months and 52 occurred >6 months) and 183 (12%) were lost to follow-up. Probability of survival [95% confidence interval (CI)] was 97.5% (96.7% to 98.2%) at 6 months, 96.6% (95.6% to 97.4%) at 1 year, and 93.5% (91.9% to 94.8%) at 5 years. Probability of being alive and on follow-up was 80.8% (78.5% to 82.8%) at 5 years. Early mortality was associated with anemia [adjusted hazard ratio (aHR) 3.6, 95% CI: 1.7 to 7.5] and low CD4 count (aHR 1.6, 95% CI: 1.1 to 2.2 per 50 cells decrease) at treatment initiation. Long-term mortality was associated with persistent anemia (aHR 4.9, 95% CI: 2.1 to 11.6), CD4 increase from baseline <50 cells per cubic millimeter (aHR 3.1, 95% CI: 1.6 to 5.7), and viral load >1000 copies per milliliter (aHR 2.8, 95% CI: 1.3 to 6.1) at 6 months of HAART; male gender; and calendar year of enrollment. Conclusions:Early mortality was associated with anemia and severe immunosuppression at initiation of therapy. Long-term mortality was associated with persistent anemia, CD4 count increase, and virological response at 6 months of therapy over baseline characteristics, highlighting the importance of laboratory monitoring.

Development of a one-step immunochromatographic strip test for the rapid detection of nevirapine (NVP), a commonly used antiretroviral drug for the treatment of HIV/AIDS

Currently, high-performance liquid chromatographic (HPLC) methods are mainly used to measure antiretroviral plasma concentrations in HIV-infected patients. Although the utility of routine therapeutic drug monitoring (TDM) as an additional tool to optimize long-term antiretroviral therapy is unclear, if TDM is to be widely used, the availability of simple, cheap and reliable methods for the measurement of antiretroviral drug levels are needed, particularly in resource-limited settings. In this study, an immunochromatograhic (IC) strip test to detect the presence of nevirapine (NVP) in body fluids has been developed. Antiserum to NVP was first raised in rabbits by immunization against NVP chemically conjugated with bovine serum albumin, and subsequently validated by Western immunoblotting and competitive indirect ELISA. The partially purified anti-NVP antibodies were conjugated with colloidal gold particles. The conjugation of the colloidal gold and polyclonal antibodies was monitored by UV-vis spectroscopy, while transmission electron microscopy images were used to characterize the particle size and shape of the conjugates. The resulting colloidal gold conjugates were used for the production of an IC strip test to detect nevirapine in human plasma. Preliminary assessment suggests no-cross reactivity of the NVP polyclonal antibodies but assessment of plasma samples from HIV-infected patients receiving HAART needs to be conducted. This assay could potentially be used for drug monitoring as part of the clinical care of HIV infected patients.

Raltegravir pharmacokinetics during pregnancy.

Objective:We evaluated the pharmacokinetics (PK) of raltegravir in HIV-infected women during pregnancy and postpartum. Methods:International Maternal Pediatric Adolescent AIDS Clinical Trials 1026s is an ongoing prospective study of antiretroviral PK during pregnancy (NCT00042289). Women receiving 400 mg raltegravir twice daily in combination antiretroviral therapy had intensive steady-state 12-hour PK profiles performed during pregnancy and at 6- to 12-week postpartum. Targets were trough concentration above 0.035 &mgr;g/mL, the estimated 10th percentile in nonpregnant historical controls. Results:Median raltegravir area under the curve was 6.6 &mgr;g·h/mL for second trimester (n = 16), 5.4 &mgr;g·h/mL for third trimester (n = 41), and 11.6 &mgr;g·h/mL postpartum (n = 38) (P = 0.03 postpartum vs second trimester, P = 0.001 pp vs third trimester). Trough concentrations were above the target in 69%, 80%, and 79% of second trimester, third trimester, and postpartum subjects, respectively, with wide variability (<0.010–0.917 &mgr;g/mL), and no significant difference between third trimester and postpartum trough concentrations was detected. The median ratio of cord blood/maternal raltegravir concentrations was 1.5. HIV RNA levels were <400 copies per milliliter in 92% of women at delivery. Adverse events included elevated liver transaminases in 1 woman and vomiting in 1. All infants with known status are HIV uninfected. Conclusions:Median raltegravir area under the curve was reduced by approximately 50% during pregnancy; trough concentrations were frequently below target both during late pregnancy and postpartum. Raltegravir readily crossed the placenta. High rates of viral suppression at delivery and the lack of a clear relationship between raltegravir concentration and virologic effect in nonpregnant adults suggest that despite the decreased exposure during pregnancy, a higher dose is not necessary.

A Chewable Pediatric Fixed-dose Combination Tablet of Stavudine, Lamivudine, and Nevirapine: Pharmacokinetics and Safety Compared With the Individual Liquid Formulations in Human Immunodeficiency Virus-infected Children in Thailand

Background: Pediatric fixed-dose combinations (FDCs) are needed to facilitate antiretroviral therapy in children. We evaluated the relative bioavailability, safety, and therapeutic adequacy of a novel chewable pediatric FDC tablet of stavudine (7 mg), lamivudine (30 mg), and nevirapine (50 mg), referred to as GPO-VIR S7, and compared it with the individual original brand-name liquid formulations in human immunodeficiency virus-infected Thai children. Methods: The International Maternal Pediatric Adolescent AIDS Clinical Trials group (IMPAACT) P1056 study was a phase I/II, 2-arm, randomized, open-label, multidose pharmacokinetic cross-over study. Children ≥6 to ≤30 kg receiving nevirapine-based HAART for at least 4 weeks were randomized to receive GPO-VIR S7 chewable tablets or the equivalent liquid formulations. Children were stratified by weight and dosing was weight-based. Intensive 12-hour blood sampling was performed on day 28, and subjects then crossed-over to the alternate formulation at equal doses with identical 12-hour sampling on day 56. Pharmacokinetic indices were determined by noncompartmental analysis. Results: Thirty-four children completed the study. While taking Government Pharmaceutical Organization (GPO)-VIR S7 the geometric mean (90% CI) area under the curve was 1.54 &mgr;g·hr/mL (1.42–1.67) for stavudine, 6.39 (5.82–7.00) for lamivudine, and 74.06 (65.62–83.60) for nevirapine. Nevirapine drug exposure for GPO-VIR S7 was therapeutically adequate. Geometric mean area under the curve ratios (90% CI) of GPO-VIR S7/liquid formulation for stavudine, lamivudine, and nevirapine were 0.97 (0.92–1.02), 1.41 (1.30–1.53), and 1.08 (1.04–1.13), respectively. No serious drug-related toxicity was reported. Conclusions: The chewable FDC was safe and provided therapeutically adequate plasma drug exposures in human immunodeficiency virus-infected children. Substituting the FDC for liquid formulations can simplify antiretroviral therapy.

Pharmacokinetics and safety of a new paediatric fixed-dose combination of zidovudine/lamivudine/nevirapine in HIV-infected children.

BACKGROUND Alternatives to the available stavudine-containing paediatric fixed-dose combination (FDC) tablets are rapidly needed due to concerns regarding the cumulative toxicity of long-term stavudine exposure. We report the bioavailability and short-term safety of a novel paediatric FDC tablet of zidovudine (ZDV)/lamivudine (3TC)/nevirapine (NVP; 30/15/28 mg) in HIV-infected children. METHODS In this Phase I/II open-label pharmacokinetic study, 42 children weighing 6-30 kg treated with NVP-based HAART for ≥4 weeks were randomized to receive the FDC tablets (GPO-VIR Z30) or the liquid formulations. Dosing was weight-based. Intensive 12-h blood sampling was performed after 2 weeks; subjects then crossed-over to the alternate formulation at equal doses and sampling repeated 2 weeks later. Pharmacokinetic parameters were determined by non-compartmental analysis. Buccal-swab samples were collected for cytochrome P450 (CYP)2B6 polymorphism analysis. RESULTS With the FDC tablet, the geometric mean (90% CI) area under the curve (AUC) for ZDV, 3TC and NVP was 1.58 (1.49-1.68), 7.78 (7.38-8.19) and 68.88 (62.13-76.36) μg•h/ml, respectively. Rules for NVP therapeutic inadequacy were defined a priori, and despite lower NVP exposure with the tablet (P<0.001), the levels remained therapeutically adequate. ZDV AUC was similar between formulations. 3TC exposure was significantly higher with the tablet but comparable to historical data in adults and children taking branded tablets. While receiving the tablet, NVP AUC in children with CYP2B 516 GG (45%), GT (45%) and TT (10%) genotypes were 67.0, 74.5 and 106.4 μg•h/ml, respectively (P=0.04). CONCLUSIONS Disparities in drug exposure between formulations were observed; however, the FDC tablet delivered therapeutically adequate exposures of each drug and could well play an important role in simplifying antiretroviral treatment for children.

Pharmacogenetic markers of CYP2B6 associated with efavirenz plasma concentrations in HIV‐1 infected Thai adults

AIMS To investigate the frequency of CYP2B6 polymorphisms and the influence of haplotype structure on plasma efavirenz concentrations in Thai adults with HIV-1 infection. METHODS Genotyping of nine single nucleotide polymorphisms (SNPs, c.64C>T, c.499C>G, c.516G>T, c.785A>G, c.1375A>G, c.1459C>T, g.3003T>C, g.18492C>T and g.21563C>T) of CYP2B6 were performed using real-time PCR-based allelic discrimination on blood samples from 52 HIV-infected adults who had received an efavirenz-based regimen. Plasma efavirenz concentrations were measured by high performance liquid chromatography. RESULTS The minor allele frequencies for c.64C>T, c.516G>T, c.785A>G, g.3003C>T, g.18492T>C and g.21563C>T were 0.087, 0.365, 0.413, 0.308 and 0.356, respectively. However, no variant alleles were identified for three SNPs (c.499 C>G, c.1375 A>G and c.1459 C>T). Efavirenz plasma concentrations were significantly associated with c.516G>T (P= 0.0095), c.785A>G (P= 0.0017), g.21563C>T (P= 0.0036) and g.18492C>T (P= 0.0011). The composite CYP2B6 of three SNPs (c.516G ≥ T, c.785A ≥ G and g.21563C ≥ T) genotypes were significantly associated with higher efavirenz concentrations. CONCLUSIONS Our data indicate that the GAC-CYP2B6 haplotype is associated with higher plasma efavirenz concentrations in HIV-infected Thai adults.

Efficacy and Safety of 1-Month Postpartum Zidovudine-Didanosine to Prevent HIV-Resistance Mutations after Intrapartum Single-Dose Nevirapine

BACKGROUND Intrapartum single-dose nevirapine plus third trimester maternal and infant zidovudine are essential components of programs to prevent mother-to-child transmission of human immunodeficiency virus (HIV) in resource-limited settings. The persistence of nevirapine in the plasma for 3 weeks postpartum risks selection of resistance mutations to nonnucleoside reverse-transcriptase inhibitors (NNRTIs). We hypothesized that a 1-month zidovudine-didanosine course initiated at the same time as single-dose nevirapine (sdNVP) would prevent the selection of nevirapine-resistance mutations. METHODS HIV-infected pregnant women in the PHPT-4 cohort with CD4 cell counts >250 cells/mm3 received antepartum zidovudine from the third trimester until delivery, sdNVP during labor, and a 1-month zidovudine-didanosine course after delivery. These women were matched on the basis of baseline HIV load, CD4 cell count, and duration of antepartum zidovudine to women who received sdNVP in the PHPT-2 trial (control subjects). Consensus sequencing and the more sensitive oligonucleotide ligation assay were performed on samples obtained on postpartum days 7-10, 37-45, and 120 (if the HIV load was >500 copies/mL) to detect K103N/Y181C/G190A mutations. RESULTS The 222 PHPT-4 subjects did not differ from matched control subjects in baseline characteristics except for age. The combined group median CD4 cell count was 421 cells/mm3 (interquartile range [IQR], 322-549 cells/mm3), the median HIV load was 3.45 log10 copies/mL (IQR, 2.79-4.00 log10 copies/mL), and the median duration of zidovudine prophylaxis was 10.4 weeks (IQR, 9.1-11.4 weeks). Using consensus sequencing, major NNRTI resistance mutations were detected after delivery in 0% of PHPT-4 subjects and 10.4% of PHPT-2 controls. The oligonucleotide ligation assay detected resistance in 1.8% of PHPT-4 subjects and 18.9% of controls. Major NNRTI resistance mutations were detected by either method in 1.8% of PHPT-4 subjects and 20.7% of controls (P < .001). CONCLUSIONS A 1-month postpartum course of zidovudine plus didanosine prevented the selection of the vast majority of NNRTI resistance mutations.