Antiretroviral pharmacokinetics in the paediatric population: a review

Abstract

Characteristics unique to paediatric pharmacotherapy should be considered when treating children infected with human immunodeficiency virus (HIV). Processes of growth and development in the paediatric patient can significantly affect drug absorption and disposition. Immature renal function, altered hepatic enzyme activity and differences in drug absorption lead to variations in systemic exposure of antiretrovirals among children. Paediatric patients are also subject to unique circumstances that may prevent adherence to antiretroviral regimens. The pharmacokinetics of nucleoside reverse transcriptase inhibitors differ significantly among preterm infants, full-term infants and older children. Decreased hepatic glucuronidation activity in neonates results in pharmacokinetic differences in zidovudine disposition when compared with older children. Didanosine, stavudine and lamivudine are renally eliminated, thus resulting in differences among young children with immature renal function. Pharmacokinetic data for non-nucleoside reverse transcriptase inhibitors in children are limited. Decreased elimination of nevirapine among neonates has been observed, primarily due to decreased enzymatic activity. Pharmacokinetic differences across age groups have been noted for efavirenz, but no formal assessments have been conducted in children weighing less than 10kg. Protease inhibitors are metabolised by the cytochrome P450 enzyme system, which is not fully developed in younger children. Decreased metabolism can result in elevated plasma concentrations, thereby increasing the chance of toxicity. Unfortunately, few studies exist evaluating the pharmacokinetics of antiretrovirals in children. As a result, dosage selection of antiretrovirals in children often occurs without adequate data. As the life expectancy of HIV-infected children increases, use of antiretrovirals to prevent disease progression also increases. If prevention of treatment failure continues to be the goal of antiretroviral therapy, the pharmacokinetics of antiretrovirals in children need to be assessed early in the drug development process.