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

Lamivudine dosing for preterm infants exposed to HIV: a population pharmacokinetic modelling and simulation study

OBJECTIVES

To develop a pragmatic twice daily lamivudine dosing strategy for preterm infants from 24 to 37 completed weeks of gestation.

METHODS

Data were combined from eight pharmacokinetic studies in neonates and infants receiving lamivudine oral solution. A population pharmacokinetic model was developed using non-linear mixed effects regression. Different lamivudine dosing strategies, stratified by gestational age at birth (GA) bands, were simulated in a virtual population of preterm infants, aimed at maintaining lamivudine drug exposures (AUC0-12) within a reference target range of 2.95 to 13.25 µg·h/mL, prior to switching to WHO-weight band doses when ≥4 weeks of age and weighing ≥3 kg.

RESULTS

A total of 154 infants (59% female) contributed 858 lamivudine plasma concentrations. Median (range) GA at birth was 38 (27-41) weeks. At the time of first pharmacokinetic sampling infants were older with median postnatal age (PNA) of 6.3 (0.52-26.6) weeks. Lamivudine concentrations were described by a one-compartment model, with CL/F and V/F allometrically scaled to weight. Maturation of CL/F was described using an Emax model based on PNA. CL/F was also adjusted on GA to allow extrapolation for extreme prematurity. Simulations predicted an optimal lamivudine dosing for infants GA ≥24 to <30 weeks of 2 mg/kg twice daily from birth until weighing 3 kg; and for GA ≥30 to <37 weeks, 2 mg/kg twice daily for the first 4 weeks of life, followed by 4 mg/kg twice daily until weighing 3 kg.

CONCLUSIONS

Model-based predictions support twice daily pragmatic GA band dosing of lamivudine for preterm infants, but clinical validation is warranted.

Comparison of three galenic forms of lamivudine in young West African children living with Human Immunodeficiency Virus

Background

Few pharmacokinetic data were reported on dispersible tablets despite their increasing use. One hundred fifty HIV-infected children receiving lamivudine were enrolled in the MONOD ANRS 12,206 trial. Three galenic forms were administered: liquid formulation, tablet form and dispersible scored tablet.

Method

HIV-infected children <4 years old were enrolled in the MONOD ANRS 12,206 trial designed to assess the simplification of a successful 12-months lopinavir-based antiretroviral treatment with efavirenz. Lamivudine plasma concentrations were analysed using nonlinear mixed effects modelling approach.

Results

One hundred and fifty children (age: 2.5 years (1.9–3.2), weight 11.1 (9.5–12.5) kg (median (IQR)) were included in this study. Over the study period, 79 received only the syrup form, 29 children switched from syrup form to tablet 3TC/AZT form, 36 from syrup to the orodispersible ABC/3TC form and two from the 3TC/AZT form to the orodispersible ABC/3TC form. The 630 lamivudine concentrations were best described by a two-compartment model allometrically scaled. Galenic form had no significant effect on 3TC pharmacokinetic.

Conclusion

This trial provided an opportunity to compare three galenic forms (liquid formulation, tablet form and dispersible scored tablet) of lamivudine in the target population of young HIV–1-infected children. Galenic form had no significant effect on lamivudine pharmacokinetics.

Potential pharmacokinetic interaction between orally administered drug and osmotically active excipients in pediatric polypharmacy

Poorly absorbable sugar alcohols (e.g., mannitol, sorbitol, and maltitol) are the excipients frequently contained in pediatric dosage forms. Due to their osmotically active properties, certain amount of sugar alcohols reportedly reduces oral bioavailability of concomitant drugs. This fact implies the possible pharmacokinetic interaction between orally administered drug and sugar alcohols which are present in other concomitant medications. The purpose of this study was to identify the possibility and likeliness of the osmotically active excipient-induced pharmacokinetic interaction in pediatric polypharmacy. Previously developed in silico model that captured the osmotic effect of sugar alcohols in adults was expanded to pediatric population. This mathematical model successfully explained the impaired bioavailability of lamivudine by the co-administered sorbitol in other dosage forms. In the meantime, sugar alcohol contents in marketed pediatric dosage forms were investigated by reverse engineering technology. Considering the critical administration dose of sugar alcohols estimated by in silico model, it was revealed that 25 out of 153 pediatric dosage forms were identified as possible perpetrators even under the approved administration and dosage in Japan. This study shed light on the potential pharmacokinetic interaction that cannot be dismissed throughout the pediatric pharmaceutical dosage form design and development.

Development of a Pediatric Relative Bioavailability/Bioequivalence Database and Identification of Putative Risk Factors Associated With Evaluation of Pediatric Oral Products

Generally, bioequivalence (BE) studies of drug products for pediatric patients are conducted in adults due to ethical reasons. Given the lack of direct BE assessment in pediatric populations, the aim of this work is to develop a database of BE and relative bioavailability (relative BA) studies conducted in pediatric populations and to enable the identification of risk factors associated with certain drug substances or products that may lead to failed BE or different pharmacokinetic (PK) parameters in relative BA studies in pediatrics. A literature search from 1965 to 2020 was conducted in PubMed, Cochrane Library, and Google Scholar to identify BE studies conducted in pediatric populations and relative BA studies conducted in pediatric populations. Overall, 79 studies covering 37 active pharmaceutical ingredients (APIs) were included in the database: 4 bioequivalence studies with data that passed BE evaluations; 2 studies showed bioinequivalence results; 34 relative BA studies showing comparable PK parameters, and 39 relative BA studies showing differences in PK parameters between test and reference products. Based on the above studies, common putative risk factors associated with differences in relative bioavailability (DRBA) in pediatric populations include age-related absorption effects, high inter-individual variability, and poor study design. A database containing 79 clinical studies on BE or relative BA in pediatrics has been developed. Putative risk factors associated with DRBA in pediatric populations are summarized.

Effects of Sorbitol on the Pharmacokinetics of Lamivudine Solution and the FDA's Decision to Increase the Dose of Lamivudine Solution for Pediatric Patients

The article by Adkison et al. described sorbitol effects on lamivudine exposures. The results indicate a plausible mechanism for lower lamivudine exposures in pediatric patients receiving the solution formulation with concomitant medications containing sorbitol. In this commentary, we discuss lower lamivudine exposures in pediatric patients receiving the solution formulation, the impact of sorbitol on lamivudine exposures, and the US Food and Drug Administration's (FDA's) decision to increase the dose of the lamivudine solution for all pediatric patients.

Effect of Sorbitol on the Pharmacokinetic Profile of Lamivudine Oral Solution in Adults: An Open-Label, Randomized Study

In children aged ≤4 years, the relative bioavailability of lamivudine oral solution was 37% lower than that of a tablet formulation. An open-label, four-way crossover study was conducted in healthy adults to evaluate the effect of sorbitol, a common liquid excipient, on the pharmacokinetics of lamivudine oral solution (ClinicalTrials.gov identifier, NCT02634073). Sixteen subjects were randomized to one of four sequences consisting of four doses of lamivudine 300 mg (10 mg/mL) alone or with sorbitol 3.2, 10.2, or 13.4 g. Sorbitol 3.2, 10.2, and 13.4 g decreased lamivudine maximum concentration (C_max ) by 28%, 52%, and 55% and area under the concentration-time curve from time 0 to 24 h (AUC_0-24 ) by 20%, 39%, and 44%, respectively. Three subjects (19%) reported five nonserious adverse events (one drug-related). The dose-dependent effects of sorbitol on lamivudine C_max and AUC_0-24 reveal an absorption-based interaction that may decrease lamivudine exposure in patients coadministered sorbitol-containing medicines.

K. HK, Ramachandran G, Shet A. Sub-therapeutic nevirapine concentration during antiretroviral treatment initiation among children living with HIV: Implications for therapeutic drug monitoring

Nevirapine, a component of antiretroviral therapy (ART) in resource-limited settings, known for auto-induction of metabolism, is initiated at half therapeutic dose until day 14 (‘lead-in period’), and subsequently escalated to full dose. However, studies have shown that this dosing strategy based on adult studies may not be appropriate in children, given that younger children have higher drug clearance rates. In this prospective cohort study, we studied trough plasma nevirapine levels by high performance liquid chromatography (HPLC) at days 7, 14 (lead-in period) and 28 (full dose period) after ART initiation amongst HIV-1 infected children initiating nevirapine-based ART in southern India. Among the 20 children (50% male, median age 9 years) included in the study, sub-therapeutic trough plasma nevirapine concentration (<4μg/ml) was seen in 65% (13/20) of children during the lead-in period within two weeks of ART initiation and among 10% of children at 4 weeks during full-dose nevirapine. Adherence was documented as ≥95% in all children by both caregiver self-report and pill count. Median nevirapine concentrations achieved at week 1 was 4.8 μg/ml, significantly lower than 8 μg/ml, the concentration achieved at week 4 (p = 0.034). Virological failure at one year of ART was observed in six children, and was not associated with median nevirapine concentration achieved during week 1, 2 or 4. We conclude that the dose escalation strategy currently practiced among young children living with HIV-1 resulted in significant subtherapeutic nevirapine concentration (≤4μg/ml) during the lead-in period. We call for a closer look at pediatric-focused dosing strategies for nevirapine initiation in young children. Further studies to establish age-appropriate threshold nevirapine concentration are warranted in young children to corroborate the role of therapeutic drug monitoring in predicting virological outcome.

Dose evaluation of lamivudine in human immunodeficiency virus-infected children aged 5 months to 18 years based on a population pharmacokinetic analysis

AIM

The objectives of this study were to characterize age-related changes in lamivudine pharmacokinetics in children and evaluate lamivudine exposure, followed by dose recommendations for subgroups in which target steady state area under the daily plasma concentration-time curve (AUC_0-24h ) is not reached.

METHODS

Population pharmacokinetic modelling was performed in NONMEM using data from two model-building datasets and two external datasets [n = 180 (age 0.4-18 years, body weight 3.4-60.5 kg); 2061 samples (median 12 per child); daily oral dose 60-300 mg (3.9-17.6 mg kg^-1 )]. Steady state AUC_0-24h was calculated per individual (adult target 8.9 mg·h l^-1 ).

RESULTS

A two-compartment model with sequential zero order and first order absorption best described the data. Apparent clearance and central volume of distribution (% RSE) were 13.2 l h^-1 (4.2%) and 38.9 l (7.0%) for a median individual of 16.6 kg, respectively. Bodyweight was identified as covariate on apparent clearance and volume of distribution using power functions (exponents 0.506 (20.2%) and 0.489 (32.3%), respectively). The external evaluation supported the predictive ability of the final model. In 94.5% and 35.8% of the children with a body weight >14 kg and <14 kg, respectively, the target AUC_0-24h was reached.

CONCLUSION

Bodyweight best predicted the developmental changes in apparent lamivudine clearance and volume of distribution. For children aged 5 months-18 years with a body weight <14 kg, the dose should be increased from 8 to 10 mg kg^-1  day^-1 if the adult target for AUC_0-24h is aimed for. In order to identify whether bodyweight influences bioavailability, clearance and/or volume of distribution, future analysis including data on intravenously administered lamivudine is needed.

Effect of diurnal variation, CYP2B6 genotype and age on the pharmacokinetics of nevirapine in African children

OBJECTIVES

To characterize the effects of CYP2B6 polymorphisms, diurnal variation and demographic factors on nevirapine pharmacokinetics in African children.

METHODS

Non-linear mixed-effects modelling conducted in NONMEM 7.3 described nevirapine plasma concentration-time data from 414 children aged 0.3-15 years.

RESULTS

Nevirapine pharmacokinetics was best described using a one-compartment disposition model with elimination through a well-stirred liver model accounting for a first-pass effect and transit-compartment absorption. Intrinsic clearance was affected by diurnal variation (characterized using a cosine function with peak amplitude 29% at 12 noon) and CYP2B6 metabolizer status [extensive metabolizer (EM) 516GG|983TT, reference; intermediate metabolizer (IM) 516GT|983TT or 516GG|983TC, 17% lower; slow metabolizer (SM) 516TT|983TT or 516GT|983TC, 50% lower; ultra-slow metabolizer (USM) 516GG|983CC, 68% lower]. Age was found to affect pre-hepatic bioavailability: 31.7% lower at birth and increasing exponentially. Median (90% CI) evening Cmin values in the different metabolizer groups were 5.01 (3.01-7.47), 6.55 (3.65-13.32), 11.59 (5.44-22.71) and 12.32 (12.32-27.25) mg/L, respectively. Evening Cmin values were <3 mg/L in 43% of EM weighing <6 kg and 26% of IM weighing <6 kg, while 73% of SM and 88% of USM in all weight-bands had evening Cmin values >8 mg/L. Cmin was not markedly affected by administration time, but was altered by unequal splitting of the daily dose.

CONCLUSIONS

Diurnal variation does not greatly affect nevirapine exposure. However, when daily doses cannot be split equally, the larger dose should be given in the morning. To achieve homogeneous exposures, nevirapine doses for SM and USM should be reduced by 50%, and children weighing <6 kg with EM or IM metabolizer status should receive the same dose as children weighing 6-10 kg.

Optimization of the strength of the efavirenz/lamivudine/abacavir fixed-dose combination for paediatric patients

BACKGROUND

Child-friendly, low-cost, solid, oral fixed-dose combinations (FDCs) of efavirenz with lamivudine and abacavir are urgently needed to improve clinical management and drug adherence for children.

METHODS

Data were pooled from several clinical trials and therapeutic drug monitoring datasets from different countries. The number of children/observations was 505/3667 for efavirenz. Population pharmacokinetic analyses were performed using a non-linear mixed-effects approach. For abacavir and lamivudine, data from 187 and 920 subjects were available (population pharmacokinetic models previously published). Efavirenz/lamivudine/abacavir FDC strength options assessed were (I) 150/75/150, (II) 120/60/120 and (III) 200/100/200 mg. Monte Carlo simulations of the different FDC strengths were performed to determine the optimal dose within each of the WHO weight bands based on drug efficacy/safety targets.

RESULTS

The probability of being within the target efavirenz concentration range 12 h post-dose (1-4 mg/L) varied between 56% and 60%, regardless of FDC option. Option I provided a best possible balance between efavirenz treatment failure and toxicity risks. For abacavir and lamivudine, simulations showed that for option I >75% of subjects were above the efficacy target.

CONCLUSIONS

According to simulations, a paediatric efavirenz/lamivudine/abacavir fixed-dose formulation of 150 mg efavirenz, 75 mg lamivudine and 150 mg abacavir provided the most effective and safe concentrations across WHO weight bands, with the flexibility of dosage required across the paediatric population.

Safe and effective pharmacotherapy in infants and preschool children: importance of formulation aspects

Safe and effective paediatric pharmacotherapy requires careful evaluation of the type of drug substance, the necessary dose and the age-appropriateness of the formulation. Generally, the younger the child, the more the attention that is required. For decades, there has been a general lack of (authorised) formulations that children are able to and willing to take. Moreover, little was known on the impact of pharmaceutical aspects on the age-appropriateness of a paediatric medicine. As a result of legislative incentives, such knowledge is increasingly becoming available. It has become evident that rapidly dissolving tablets with a diameter of 2 mm (mini-tablets) can be used in preterm neonates and non-rapidly dissolving 2 mm mini-tablets in infants from 6 months of age. In addition, uncoated 4 mm mini-tablets can be used in infants from the age of 1 year. Also, there is some evidence that children prefer mini-tablets over a powder, suspension or syrup. Other novel types of age-appropriate oral formulations such as orodispersible films may further add to the treatment possibilities. This review provides an overview of the current knowledge on oral formulations for infants and preschool children, the advantages and disadvantages of the different types of dosage forms and the age groups by which these can likely be used.

The Need for Pediatric Formulations to Treat Children with HIV

Over 3.2 million children worldwide are infected with HIV, but only 24% of these children receive antiretroviral therapy (ART). ART adherence among children is a crucial part of managing human-immunodeficiency virus (HIV) infection and extending the life and health of infected children. Important causes of poor adherence are formulation- and regimen-specific properties, including poor palatability, large pill burden, short dosing intervals, and the complex storage and transportation of drugs. This review aims to summarize the various regimen- and formulation-based barriers to ART adherence among children to support the need for new and innovative pediatric formulations for antiretroviral therapy (ART). Detailing the arguments both for and against investing in the development of pediatric HIV medications, as well as highlighting recent advances in pediatric ART formulation research, provides a synopsis of the current data related to pediatric ART formulations and adherence.

Plasma pharmacokinetics of once-daily abacavir- and lamivudine-containing regimens and week 96 efficacy in HIV-infected Thai children

BACKGROUND

Abacavir and lamivudine are approved for once-daily use in HIV-infected adults. Limited pharmacokinetic (PK) data for abacavir and lamivudine in children are available.

METHODS

A crossover study to compare PK of once- versus twice-daily abacavir and lamivudine was conducted in virologically suppressed HIV-infected Thai children aged <18years, with bodyweight of at least 14 kg, HIV RNA <50 copies/mL and HLA-B*5701 negative. Abacavir and lamivudine daily doses by bodyweight were 300 and 150 mg for 14-<20 kg, 450 and 300 mg for 20-<25 kg, and 600 and 300 mg for ≥25 kg, respectively. Originator abacavir and lamivudine scored tablets were administered. Intensive PK sampling was performed after 14 days of each dose. PK parameters were determined using non-compartmental analysis.

RESULTS

Thirty children (57% male) were enrolled, 10 per weight band. Median (IQR) age was 8.8 (6.6-11.3) years and bodyweight was 21.9 (19.2-30.6) kg. The geometric means (GM) AUC0-24 of once- and twice-daily abacavir were 14.43 and 10.65 mg.h/L, respectively. The geometric mean ratio (GMR) of AUC0-24 for once- versus twice-daily abacavir dosing was 1.36 [90% confidence interval (CI) 1.11-1.66]. The GM AUC0-24 of once- and twice-daily lamivudine were 17.70 and 18.11 mg.h/L, respectively. The GMR of AUC0-24 for once- versus twice-daily lamivudine dosing was 0.98 (90% CI 0.84-1.14). At 96 weeks, 90% had HIV RNA <50 copies/mL and there were no serious adverse events.

CONCLUSION

Abacavir exposure was greater with once-daily dosing, while lamivudine once- and twice-daily exposures were bioequivalent. Once-daily abacavir and lamivudine using weight-band dosing is a treatment option for children.

Pharmacokinetics of nevirapine, stavudine and lamivudine in Indian HIV-infected children receiving generic fixed dose combinations

OBJECTIVE

To determine the trough and two hour plasma levels of nevirapine, stavudine, and lamivudine when administered in fixed dose combinations (FDC).

DESIGN

Cross sectional.

SETTING

Tertiary care hospital in Northern India.

PARTICIPANTS

79 HIV-infected children receiving antiretroviral therapy with FDCs for more than month.

INTERVENTION

Two-point sampling (0 and 2 hours after the morning dose).

OUTCOME MEASURES

Plasma concentrations of all three drugs were simultaneously assayed by liquid chromatography/mass spectroscopy.

RESULTS

Majority (77%) of children were receiving fixed dose combination of stavudine, lamivudine, nevirapine in the ratio of 6:30:50 mg. The median (IQR) trough and 2-hour plasma levels (µg/mL) of nevirapine, stavudine and lamivudine were 5.2 (4.0, 6.3) and 7.9 (6.0, 9.7); 0.1 (0.06, 0.16) and 1.1 (0.59, 1.6); 0.1 (0.02, 0.2) and 2.5 (1.4, 3.1), respectively. Very few children had sub-therapeutic plasma drug levels of stavudine (2.5%), lamivudine (7.6%) and nevirapine (10%). Inadequate viral suppression at 6 months follow up was significantly associated with initial high viral load, low CD4 percentage at the time of enrolment in study, and lower doses of lamivudine and stavudine.

CONCLUSIONS

The currently available generic pediatric fixed dose antiretroviral combinations in India provide adequate drug exposure in majority of children.

Formulations for children: problems and solutions

Paediatric formulation design is complex as there is a need to understand the developmental physiological changes that occur during childhood and their impact on the absorption of drugs. Paediatric dose adjustments are usually based on achieving pharmacokinetic or pharmacodynamic profiles equivalent to those achieved in adult populations. However, differences in the way in which children handle adult products or the use of bespoke paediatric formulations can result in unexpected pharmacokinetic drug profiles with altered clinical efficacy. Differences in drug formulations need to be understood by healthcare professionals involved in the prescribing, administration or dispensing of drugs to children such that appropriate advice is given to ensure that therapeutic outcomes are achieved. This issue is not confined to oral medicines but is applicable for all routes of administration encountered in paediatric therapy.

Pediatric drug formulations: a review of challenges and progress

Children differ from adults in many aspects of pharmacotherapy, including capabilities for drug administration, medicine-related toxicity, and taste preferences. It is essential that pediatric medicines are formulated to best suit a child's age, size, physiologic condition, and treatment requirements. To ensure adequate treatment of all children, different routes of administration, dosage forms, and strengths may be required. Many existing formulations are not suitable for children, which often leads to off-label and unlicensed use of adult medicines. New regulations, additional funding opportunities, and innovative collaborative research initiatives have resulted in some recent progress in the development of pediatric formulations. These advances include a paradigm shift toward oral solid formulations and a focus on novel preparations, including flexible, dispersible, and multiparticulate oral solid dosage forms. Such developments have enabled greater dose flexibility, easier administration, and better acceptance of drug formulations in children. However, new pediatric formulations address only a small part of all therapeutic needs in children; moreover, they are not always available. Five key issues need to be addressed to stimulate the further development of better medicines for children: (1) the continued prioritization of unmet formulation needs, particularly drug delivery in neonates and treatment gaps in pediatric cancers and childhood diseases in developing countries; (2) a better use of existing data to facilitate pediatric formulation development; (3) innovative technologies in adults that can be used to develop new pediatric formulations; (4) clinical feedback and practice-based evidence on the impact of novel formulations; and (5) improved access to new pediatric formulations.

Estimating age-based antiretroviral therapy costs for HIV-infected children in resource-limited settings based on World Health Organization weight-based dosing recommendations

BACKGROUND

Pediatric antiretroviral therapy (ART) has been shown to substantially reduce morbidity and mortality in HIV-infected infants and children. To accurately project program costs, analysts need accurate estimations of antiretroviral drug (ARV) costs for children. However, the costing of pediatric antiretroviral therapy is complicated by weight-based dosing recommendations which change as children grow.

METHODS

We developed a step-by-step methodology for estimating the cost of pediatric ARV regimens for children ages 0-13 years old. The costing approach incorporates weight-based dosing recommendations to provide estimated ARV doses throughout childhood development. Published unit drug costs are then used to calculate average monthly drug costs. We compared our derived monthly ARV costs to published estimates to assess the accuracy of our methodology.

RESULTS

The estimates of monthly ARV costs are provided for six commonly used first-line pediatric ARV regimens, considering three possible care scenarios. The costs derived in our analysis for children were fairly comparable to or slightly higher than available published ARV drug or regimen estimates.

CONCLUSIONS

The methodology described here can be used to provide an accurate estimation of pediatric ARV regimen costs for cost-effectiveness analysts to project the optimum packages of care for HIV-infected children, as well as for program administrators and budget analysts who wish to assess the feasibility of increasing pediatric ART availability in constrained budget environments.

Evaluation of nevirapine dosing recommendations in HIV-infected children

AIMS

Nevirapine (NVP) is a non-nucleoside reverse transcriptase inhibitor used for chronic human immunodeficiency virus infections in adults and children. The aims of this study were to investigate the population pharmacokinetics of NVP in children, establish factors that influence NVP pharmacokinetics and evaluate the current dosing recommendations.

METHODS

Concentrations were measured on a routine basis in 94 children aged from 2 months to 17 years. A total of 390 NVP plasma concentrations were retrospectively collected, and a population pharmacokinetic model was developed with Monolix 4.0.

RESULTS

Nevirapine pharmacokinetics was best described by a one-compartment model with first-order absorption and elimination. After standardization to a 70 kg adult using allometry, postmenstrual age had a significant effect on the bioavailability. Estimates of apparent clearance and volume of distribution were 3.9 l h(-1) (70 kg)(-1) and 140 l (70 kg)(-1) , respectively. Based on simulations of European Medicines Agency (EMA) and World Health Organization (WHO) dosing recommendations, the probability of observing minimal concentrations below the efficacy target of 3 mg l(-1) is higher following the EMA recommendations than the WHO recommendations. However, NVP underdosing persists for the 3-6 and 6-10 kg weight ranges following the WHO recommendations.

CONCLUSIONS

It is suggested to increase doses to 75 and 100 mg twice daily for the 3-6 and 6-10 kg weight ranges, respectively, in order to obtain more than 95% of children with concentrations above 3 mg l(-1) .

Developmental pharmacokinetic changes of Lamivudine in infants and children

Lamivudine is a nucleoside reverse transcriptase inhibitor widely used in infants and children in combination antiretroviral therapy to treat human immunodeficiency virus (HIV) infection. Developmental changes in lamivudine pharmacokinetic disposition were assessed by combining data from 7 studies of lamivudine (Pediatric AIDS Clinical Trials Group 300, 353, 356, 358, 386, 1056, and 1069) representing subjects across the pediatric age continuum. A population pharmacokinetic model was developed to identify factors that influence lamivudine disposition. Age and Thai race were independent predictors of apparent clearance (CL/F), whereas the use of a fixed drug combination formulation (GPO-VIR) was an independent predictor of bioavailability, with CL/F more than doubling from birth to adolescence. Serum creatinine was not associated with CL/F. Monte Carlo simulations were used to compare the lamivudine exposure achieved with World Health Organization (WHO) weight band and Food and Drug Administration (FDA) label dosing recommendations. WHO dosing yielded higher exposure during the first few months of life, but this difference was less pronounced between 6 months and 14 years of age. Overall, both FDA and WHO dosing provided similar AUC values to those previously reported in HIV-infected adults. Lamivudine WHO weight band dosing results in therapeutic exposure in infants and children and may improve drug dosing in resource-limited countries.

Managing HIV-infected children in a low-resource, public clinic: a comparison of nurse vs. clinical officer practices in ART refill, calculation of adherence and subsequent appointments

Background

In Malawi, as in other sub-Saharan African countries, nurses manage patients of all ages on antiretroviral treatment (ART). Nurse management of children is rarely studied. We compare ART prescribing between nurses and clinical officers during routine clinic visits at an urban, public clinic to inform policy in paediatric ART management.

Methods

Caregivers of children on first-line ART provided information about visit dates, pill counts, ART dosage and formulation to a nurse and, subsequently, to a clinical officer. Nurses and clinical officers independently calculated adherence, dosage based on body weight, and set next appointment date. Clinical officers, but not nurses, accessed an electronic data system that made the calculations for them based on information from prior visits, actual and expected pill consumption, and standard drug supplies. Nurses calculated with pen and paper. For numerical variables, Bland-Altman graphs plot differences of each nurse–clinical officer pair against the mean, show the 95% limits of agreement (LoA), and also show the mean difference across all reviews. Kappa statistics assess agreement for categorical variables.

Results

A total of 704 matched nurse–clinical officer reviews of 367 children attending the ART clinics between March and July 2010 were analyzed. Eight nurses and 18 clinical officers were involved; two nurses and five clinical officers managed 100 visits or more. Overall, there was a good agreement between the two cadres. Differences between nurses and clinical officers were within narrow LoA and mean differences showed little deviation from zero, indicating little skewing towards one cadre. LoA of adherence and morning and evening ART dosages varied from −24% to 24%, −0.4 to 0.4 and −0.41 to 0.40 tablets, respectively, with mean differences (95% CI) of 0.003 (−0.9, 0.91), −0.005 (−0.02, 0.01) and −0.009 (−0.02, 0.01). Next appointment calculations differed more between cadres with LoA from −40 to 42 days [mean difference: 0.96 days (95% CI:−0.6 to 2.5)], but agreement in the ART formulation prescribed was very good (kappa 0.93).

Conclusions

Nurses’ ART prescribing practices and calculations of adherence and next appointments are similar to clinical officers, although clinical officers used an electronic system. Our findings support the decision of Malawi's health officials to utilize nurses to manage paediatric ART patients.

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.

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.

Pharmacokinetics of antiretroviral drug varies with formulation in the target population of children with HIV-1

The bioequivalence of formulations is usually evaluated in healthy adult volunteers. In our study in 19 HIV-1-infected Ugandan children (1.8-4 years of age, weight 12 to <15 kg) receiving zidovudine, lamivudine, and abacavir solutions twice a day for ≥24 weeks, the use of scored tablets allowed comparison of plasma pharmacokinetics of oral solutions vs. tablets. Samples were collected 0, 1, 2, 4, 6, 8, and 12 h after each child's last morning dose of oral solution before changing to scored tablets of Combivir (coformulated zidovudine + lamivudine) and abacavir; this was repeated 4 weeks later. Dose-normalized area under curve (AUC)(0-12) and peak concentration (C(max)) for the tablet formulation were bioequivalent with those of the oral solution with respect to zidovudine and abacavir (e.g., dose-normalized geometric mean ratio (dnGMR) (tablet:solution) for zidovudine and abacavir AUC(0-12) were 1.01 (90% confidence interval (CI) 0.87-1.18) and 0.96 (0.83-1.12), respectively). However, lamivudine exposure was ~55% higher with the tablet formulation (AUC(0-12) dnGMR = 1.58 (1.37-1.81), C(max) dnGMR = 1.55 (1.33-1.81)). Although the clinical relevance of this finding is unclear, it highlights the impact of the formulation and the importance of conducting bioequivalence studies in target pediatric populations.

Antiretroviral therapy for children in resource-limited settings: current regimens and the role of newer agents

WHO antiretroviral treatment guidelines for HIV-infected children have influenced the design of treatment programmes in resource-limited settings. This review analyses the latest WHO first- and second-line regimen recommendations. The recommendation to use lopinavir/ritonavir-containing first-line regimens in young children with prior non-nucleoside reverse transcriptase inhibitor (NNRTI) exposure is based on good quality evidence. Recent research suggests that lopinavir/ritonavir-containing first-line regimens should be extended to all young children, irrespective of prior NNRTI exposure. Strategies for overcoming the adverse metabolic effects of rifampicin-containing anti-tuberculosis therapy on antiretroviral therapy regimens have been under-researched in HIV-infected children, creating uncertainty about global recommendations. Preferred second-line recommendations are largely predictable. The exception is that NNRTI-containing second-line regimens are recommended for children previously exposed to NNRTIs and who subsequently did not respond to lopinavir/ritonavir-containing first-line therapy. In these patients, second-line regimens containing newer protease inhibitors (PIs) such as darunavir and tipranavir, or integrase inhibitors such as raltegravir, should be evaluated. Newer antiretroviral agents including second-generation NNRTIs and PIs, C-C chemokine receptor type 5 inhibitors, and integrase inhibitors may assist in further refinement of existing regimen options.