Nevirapine exposure with WHO pediatric weight band dosing: enhanced therapeutic concentrations predicted based on extensive international pharmacokinetic experience.

Nevirapine (NVP) is a nonnucleoside reverse transcriptase inhibitor (NNRTI) used worldwide as part of combination antiretroviral therapy in infants and children to treat HIV infection. Dosing based on either weight or body surface area has been approved by the U.S. Food and Drug Administration (FDA) but can be difficult to implement in resource-limited settings. The World Health Organization (WHO) has developed simplified weight band dosing for NVP, but it has not been critically evaluated. NVP pharmacokinetic data were combined from eight pediatric clinical trials (Pediatric AIDS Clinical Trials Group [PACTG] studies 245, 356, 366, 377, 403, 1056, and 1069 and Children with HIV in Africa Pharmacokinetics and Adherence of Simple Antiretroviral Regimens [CHAPAS]) representing subjects from multiple continents and across the pediatric age continuum. A population pharmacokinetic model was developed to characterize developmental changes in NVP disposition, identify potential sources of NVP pharmacokinetic variability, and assess various pediatric dosing strategies and their impact on NVP exposure. Age, CYP2B6 genotype, and ritonavir were independent predictors of oral NVP clearance. The Triomune fixed-dose tablet was an independent predictor of bioavailability compared to the liquid and other tablet formulations. Monte Carlo simulations of the final model were used to assess WHO weight band dosing recommendations. The final pharmacokinetic model indicated that WHO weight band dosing is likely to result in a percentage of children with NVP exposure within the target range similar to that obtained with FDA dosing. Weight band dosing of NVP proposed by the WHO has the potential to provide a simple and effective dosing strategy for resource limited settings.

The evolution of HIV-1 reverse transcriptase in route to acquisition of Q151M multi-drug resistance is complex and involves mutations in multiple domains.

BACKGROUND: The Q151M multi-drug resistance (MDR) pathway in HIV-1 reverse transcriptase (RT) confers reduced susceptibility to all nucleoside reverse transcriptase inhibitors (NRTIs) excluding tenofovir (TDF). This pathway emerges after long term failure of therapy, and is increasingly observed in the resource poor world, where antiretroviral therapy is rarely accompanied by intensive virological monitoring. In this study we examined the genotypic, phenotypic and fitness correlates associated with the development of Q151M MDR in the absence of viral load monitoring. RESULTS: Single-genome sequencing (SGS) of full-length RT was carried out on sequential samples from an HIV-infected individual enrolled in ART rollout. The emergence of Q151M MDR occurred in the order A62V, V75I, and finally Q151M on the same genome at 4, 17 and 37 months after initiation of therapy, respectively. This was accompanied by a parallel cumulative acquisition of mutations at 20 other codon positions; seven of which were located in the connection subdomain. We established that fourteen of these mutations are also observed in Q151M-containing sequences submitted to the Stanford University HIV database. Phenotypic drug susceptibility testing demonstrated that the Q151M-containing RT had reduced susceptibility to all NRTIs except for TDF. RT domain-swapping of patient and wild-type RTs showed that patient-derived connection subdomains were not associated with reduced NRTI susceptibility. However, the virus expressing patient-derived Q151M RT at 37 months demonstrated ~44% replicative capacity of that at 4 months. This was further reduced to ~22% when the Q151M-containing DNA pol domain was expressed with wild-type C-terminal domain, but was then fully compensated by coexpression of the coevolved connection subdomain. CONCLUSIONS: We demonstrate a complex interplay between drug susceptibility and replicative fitness in the acquisition Q151M MDR with serious implications for second-line regimen options. The acquisition of the Q151M pathway occurred sequentially over a long period of failing NRTI therapy, and was associated with mutations in multiple RT domains.

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.

The impact of daily cotrimoxazole prophylaxis and antiretroviral therapy on mortality and hospital admissions in HIV-infected Zambian children.

BACKGROUND: Data on the population effectiveness of cotrimoxazole prophylaxis and antiretroviral therapy (ART) in human immunodeficiency virus (HIV)-infected African children are few. METHODS: A total of 534 Zambian children with HIV infection were randomized to receive daily cotrimoxazole prophylaxis or placebo in the Children with HIV Antibiotic Prophylaxis trial. Following trial closure, children who received the placebo initiated cotrimoxazole prophylaxis, and all children were observed in a closed cohort. Mortality and hospital admission rates were compared, over calendar time, in 9-month periods: trial recruitment (March 2001 to April 2002, May 2002 to January 2003), trial follow-up to closure (February 2003 to October 2003), initial follow-up posttrial (November 2003 to July 2004), and early and later ART availability (August 2004 to April 2005, and May 2005 to May 2006, respectively). RESULTS: A total of 546 child-years of follow-up, 40 deaths, and 80 hospital admissions were observed between the time of trial closure and June 2006. A total of 117 of 283 children who were alive at trial closure received ART in the posttrial period (median child age at first use of ART, 8.8 years). Rates decreased in both groups during the trial period, suggesting a survivorship effect. Mortality and hospital admission rates before trial closure were 14 (95% confidence interval [CI], 9-21) deaths per 100 child-years and 24 (95% CI, 15-39) hospital admissions per 100 child-years, respectively, for children who were receiving cotrimoxazole, and were 23 (95% CI, 16-34) deaths per 100 child-years and 35 (95% CI, 23-53) hospital admissions per 100 child-years, respectively, for children who were receiving the placebo. After trial closure, rates remained stable in the cotrimoxazole group, but decreased to 15 (95% CI, 8-26) deaths per 100 child-years and 19 (95% CI, 10-41) hospital admissions per 100 child-years, respectively, for the group of children who received placebo and then initiated cotrimoxazole prophylaxis. In both groups combined, mortality rates decreased to 6 (95% CI, 3-11) deaths per 100 child-years and then 2 (95% CI, 0.8-6) deaths per 100 child-years during periods of ART availability; hospital admission rates decreased to 17 (95% CI, 11-27) hospital admissions per 100 child-years and 8 (95% CI, 4-15) hospital admissions per 100 child-years, respectively. CONCLUSION: The benefits of once-daily cotrimoxazole prophylaxis continued throughout the trial and after trial closure. Mortality and hospital admissions decreased (by approximately 6-fold and approximately 3-fold, respectively) following ART availability, similar to findings observed in resource-rich countries.

Is nevirapine dose-escalation appropriate in young, African, HIV-infected children?

OBJECTIVES: Young children metabolize nevirapine faster than older children/adults. We evaluated nevirapine pharmacokinetics with or without dose-escalation in Zambian, HIV-infected infants/children and its relationship with safety/efficacy. DESIGN: A retrospective pharmacokinetic substudy of the CHAPAS-1 trial. METHODS: HIV-infected, Zambian children were randomized to initiate antiretroviral therapy (ART) with full-dose twice-daily nevirapine versus 2-week nevirapine dose-escalation. Samples taken 3-4 h postmorning-dose 2 weeks after nevirapine initiation were assayed for nevirapine levels. Viral load was measured on available samples at weeks 4 and 48; adverse events were prospectively reported. RESULTS: Of 162 (77%) children with week-2 samples, 79 (49%) were randomized to nevirapine dose-escalation. At ART initiation, median [interquartile range (IQR)] age, weight and CD4% were 5.2 (1.5-8.7) years, 13.0 (8.1-19.0) kg and 13 (8-18)%, respectively; 81 (50%) were male. With full dose, few children aged less than 2 years (3/23, 13%) or more than 2 years (4/60, 7%) had subtherapeutic nevirapine levels (defined as <3.0 mg/l), but with dose-escalation, seven out of 22 (32%) aged less than 2 years versus seven out of 57 (12%) more than 2 years had subtherapeutic nevirapine levels (P=0.05). There was no difference between week-2 nevirapine levels in those with viral load more than 250 versus less than 250 copies/ml at week 4 (P=0.97) or week 48 (P=0.40). Eleven out of 162 children had grade 1/2 rash; all were more than 2 years of age (P=0.04), and 10 were randomized to full dose. CONCLUSION: Subtherapeutic nevirapine levels 3-4 h postdose were more frequent in young children on dose-escalation. Younger children were at lower risk for rash. To simplify ART initiation and reduce the risk of suboptimal dosing, full-dose nevirapine at ART initiation should be considered for African HIV-infected children less than 2 years of age.

Pharmacokinetics of nevirapine in HIV-infected infants weighing 3 kg to less than 6 kg taking paediatric fixed dose combination tablets.

OBJECTIVES: To evaluate pharmacokinetics of nevirapine, lamivudine and stavudine in HIV-infected Zambian infants receiving fixed dose combination (FDC) antiretroviral tablets (Triomune Baby). DESIGN: Phase I/II study. METHODS: Sixteen HIV-infected children at least 1 month, weighing 3 kg to less than 6 kg were enrolled. Blood was sampled at t = 0, 2, 6 and 12 h after observed intake of one FDC tablet (50 mg nevirapine, 6 mg stavudine, 30 mg lamivudine) 4 weeks after starting treatment. Safety and viral load response over 48 weeks were determined. RESULTS: The median [interquartile range (IQR)] age, body weight and daily nevirapine dose in 15 included children (eight girls) were 4.8 (4.2, 8.4) months, 5.3 (4.3, 5.5) kg and 348 (326 385) mg/m, respectively. The median (IQR) nevirapine area under the concentration-time curve (AUC0-12 h), Cmax and C12 h were 70 (56, 104) h mg/l, 7.5 (6.2, 10) mg/l, and 4.3 (2.9, 6.9) mg/l, respectively. Values were on average higher than reported in adults, but approximately 20% lower than previously reported in children weighing at least 6 kg. Four of 15 (27%) children had a subtherapeutic nevirapine C12 h (defined as <3.0 mg/l) compared to only three of 63 (5%) children weighing at least 6 kg (P = 0.02), whereas children aged less than 5 months [three of six (50%)] may have the highest risk for subtherapeutic nevirapine C12 h (P = 0.24). No association was found between viral load values and nevirapine plasma pharmacokinetic parameters (P > 0.3). Stavudine-lamivudine pharmacokinetic parameters were broadly comparable to heavier children. CONCLUSION: Exposure to nevirapine in African, HIV-infected infants with low body weight taking FDC tablets appears on average to be adequate, but due to large intersubject variability a relatively high proportion had subtherapeutic nevirapine C12 h levels, particularly those aged less than 5 months.

Drug resistance in human immunodeficiency virus type-1 infected Zambian children using adult fixed dose combination stavudine, lamivudine, and nevirapine.

BACKGROUND: There are few medium-term virologic data in children from resource-limited settings taking adult fixed-dose-combination antiretroviral therapy (cART) without viral load monitoring. METHODS: CHAP2 (Children with HIV Antibiotic Prophylaxis 2) is a prospective cohort of Zambian children using d4T/3TC/NVP adult Triomune30 dosed according to WHO guidelines. RESULTS: A total of 103 children (19 with previous antiretroviral therapy) had follow-up >6 months. Median age at cART initiation was 8 years (IQR, 6-12) and CD4 8% (4-12). At 24 months, CD4% had increased by a median of 15% (7-25). For 74 children viral load was known/inferred: 51 of 74 (69%) had viral load <50 copies/mL (45 of 63 [71%] with no previous cART, 6 of 11 [55%] with previous cART; difference P = 0.30); 22 of 74 (30%) had viral load >1000 copies/mL. Of 26 children with resistance data, 25 (96%) had NNRTI resistance; 22 (84%) had M184V; 2 (8%) had Q151M; and 1 (4%) each had K65R, L74V, or K70E. Eight (31%) had > or =1 TAM. Those failing virologically with a genotypic sensitivity score of 0 for first-line therapy had a somewhat smaller increase in CD4% from baseline compared with those failing therapy with a genotypic sensitivity score >0 (+3 vs. +8, P = 0.13), and had somewhat lower CD4% at initiation of cART (2 vs. 11, P = 0.09). In 6 children with >1 resistance test, the estimated rate of accumulation of TAMs was 0.59/yr (95% confidence interval: 0.22-1.29). CONCLUSIONS: Twenty-four month virologic responses to cART were good. However, the rate of TAM accumulation in those with rebound was higher than reported in Western adult cohorts, and there was some indication of a detrimental effect of high level resistance on CD4% change from baseline.

Nevirapine, stavudine and lamivudine pharmacokinetics in African children on paediatric fixed-dose combination tablets.

OBJECTIVE: Triomune Baby and Junior have been developed in response to the urgent need for appropriate paediatric fixed-dose combination antiretroviral tablets, with higher nevirapine to stavudine and lamivudine ratios than adult tablets, in accordance with paediatric recommendations. We determined whether this ratio results in optimal exposure in the target population. METHODS: Seventy-one Zambian children were treated with Triomune Baby or Junior dosed according to weight bands. After 4 weeks or more, a 12-h pharmacokinetic curve was recorded. Antiretroviral plasma concentrations were assayed by high-performance liquid chromatography. RESULTS: Six children were excluded because of poor adherence. Of the remaining 65, 24 (37%) were female, 24 (37%) weighed less than 15 kg and most were malnourished. Mean (range) nevirapine C12h, Cmax and AUC12h of 6.0 (1.4, 16.9) mg/l, 10.0 (3.8, 22.5) mg/l and 94.4 (32.1, 232) mg/l per hour were higher than those reported in adults. Nevirapine C12h was subtherapeutic (< 3.0 mg/l) in four children (6%). Mean stavudine and lamivudine C12h, Cmax, AUC12h (< 0.015 mg/l, 0.45 mg/l, 1.05 mg/l per hour and 0.09 mg/l, 1.33 mg/l, 5.42 mg/l per hour) were comparable to adults. There was no evidence of a difference in nevirapine AUC12h across weight bands (P = 0.2), whereas the difference in stavudine (P = 0.0003) and lamivudine AUC12h (P = 0.01) was driven by the single weight band with unequal dosing. CONCLUSION: Nevirapine concentrations were higher but more variable than in adults; the pharmacokinetic parameters of stavudine and lamivudine were comparable to adults. As nevirapine underdosing is of greater concern than overdosing, the Triomune Baby and Junior ratio appears to be appropriate for children weighing 6 kg and over. Further research is required for children under 6 kg.