Dose-escalating study of the safety and pharmacokinetics of nelfinavir in HIV-exposed neonates

Pharmacokinetics and safety of maraviroc in neonates

OBJECTIVE

The aim of this study was to evaluate safety and pharmacokinetics of maraviroc administered with standard antiretroviral prophylaxis to HIV-1 exposed infants and to determine the appropriate dose of maraviroc during the first 6 weeks of life.

DESIGN

A phase I, multicentre, open-label study enrolling two sequential cohorts.

METHODS

IMPAACT 2007 participants enrolled by day 3 of life and were stratified by exposure to maternal efavirenz. Cohort 1 participants received two single 8 mg/kg maraviroc doses 1 week apart with pharmacokinetic sampling after each dose. Cohort 2 participants received 8 mg/kg maraviroc twice daily through 6 weeks of life with pharmacokinetic sampling at weeks 1 and 4. Maraviroc exposure target was Cavg at least 75 ng/ml. Laboratory and clinical evaluations assessed safety.

RESULTS

Fifteen Cohort 1 and 32 Cohort 2 HIV-exposed neonates were enrolled (median gestational age 39 weeks, 51% male). All 13 evaluable Cohort 1 infants met the pharmacokinetic target. Median exposure for the 25 evaluable Cohort 2 infants met the pharmacokinetic target but variability was high, with 17-33% of infants below target at Weeks 1 and 4. Pharmacokinetic target achievement was similar between efavirenz exposure strata. No Grade 3+ toxicities, early study or treatment discontinuations due to maraviroc occurred.

CONCLUSION

Median maraviroc exposure met the Cavg target in neonates receiving 8 mg/kg twice daily, although exposures were variable. Maternal efavirenz use did not impact maraviroc exposure and no discontinuations were due to maraviroc toxicity/intolerance. No infants acquired HIV-1 infection during follow-up. Maraviroc 8 mg/kg twice daily appears well tolerated during the first 6 weeks of life.

Safety of combination antiretroviral prophylaxis in high-risk HIV-exposed newborns: a retrospective review of the Canadian experience

Introduction

The optimal management of infants born to HIV-positive mothers who are untreated or have detectable viral load prior to delivery remains controversial. Despite the increasing use of combination antiretroviral therapy (cART) for post-exposure prophylaxis (PEP) of neonates at high risk of HIV infection, there is little safety and pharmacokinetic data to support this approach. The objective of this study was to evaluate the safety and tolerability of cART for PEP in HIV-exposed neonates.

Methods

Retrospective study on 148 cART and 145 Zidovudine (ZDV) monotherapy-exposed infants identified from four Canadian centres where cART for PEP has routinely been prescribed in high-risk situations. Physician-reported adverse events and clinical outcomes were extracted by chart review. Haematological and growth parameters at birth, one and six months of age were compared between cART and ZDV-exposed infants using multivariate mixed effects modelling.

Results

Non-specific signs and symptoms were reported in 10.2% of cART recipients versus none of the ZDV recipients. Treatment was discontinued prematurely in 9.5% of cART recipients versus 2.1% of ZDV recipients (p=0.01). In the multivariate model, cART recipients had lower mean haemoglobin (decrease of 2.07 g/L) over the 6-month period compared with ZDV recipients (p=0.04), but no effect was seen on absolute neutrophil count. cART recipients had lower weight and smaller head circumference at birth and one month of age compared with ZDV-exposed infants; these differences were no longer significant at six months of age.

Conclusions

cART administered at treatment doses for PEP in neonates was generally well tolerated, though a higher incidence of non-specific signs and symptoms and early treatment discontinuation occurred among cART recipients.

Pharmacokinetic considerations in the use of antivirals in neonates

INTRODUCTION

Neonatal patients, because of the inability of their immune system to properly respond to microbial challenge, are highly susceptible to viral infections. Immunoglobulins, monoclonal antibody and antiviral drugs are used for prophylaxis and treatment of viral diseases in neonates. Neonates and, especially, preterm infants differ in drug absorption, distribution, metabolism and excretion from adults and older children.

AREAS COVERED

This review will evaluate deficiencies of neonatal immune responses to microbial challenge that predispose newborns to viral infections, clinical manifestations and the treatment of viral diseases in neonates. We focus on published studies describing antiviral drug pharmacokinetics in neonates and make recommendations on the dosing of these drugs, allowing achievement of maximal clinical benefits in neonates.

EXPERT OPINION

While some efforts were undertaken to study pharmacokinetics and pharmacodynamics of antiviral drugs, much more needs to be done. Current data indicate that the pharmacokinetics of antiviral drugs may vary significantly depending on gestational age, maturation processes of drug-metabolizing enzymes and renal clearance. Specifics of pharmacokinetics of antiviral drugs need to be taken into consideration when they are prescribed to neonates and infants.

Nelfinavir and Lamivudine pharmacokinetics during the first two weeks of life

BACKGROUND

There are no previous data describing nelfinavir and lamivudine pharmacokinetics in neonates treated with weight-band dosing regimens.

DESIGN

Pharmacokinetic study of nelfinavir and lamivudine pharmacokinetics in infants during the first 2 weeks of life treated with weight-band dosing regimens.

METHODS

Intensive 12-hour pharmacokinetic profiles were performed between either days 4-7 or days 10-14 of life in 26 Brazilian infants.

RESULTS

Pharmacokinetic data were obtained from 26 infants who received median (range) per kg doses of 58.8 (48.4-79.0) mg/kg for nelfinavir and 2.0 (1.5-3.2) mg/kg for lamivudine. Median nelfinavir 12-hour AUC (AUC0-12) was 25.5 (1.7-183.5) μg*h/mL and median 12-hour concentration (C12h) was 1.09 (<0.04-14.44) μg/mL. AUC0-12 was less than 15 μg*h/mL (the 10% for adults) in 12 infants (46%). Median lamivudine AUC0-12 was 7.8 (2.7-15.6) μg*h/mL and median C12h was 0.23 (<0.04-0.74) μg/mL.

CONCLUSIONS

: Lamivudine pharmacokinetic parameters observed in this study were consistent with those seen in other studies of neonates. While median nelfinavir AUC and C12h in these neonates were above the exposure targets, interindividual variability in nelfinavir exposure was large and nelfinavir exposure failed to meet the exposure targets in 46% of infants.

Population pharmacokinetics and pharmacodynamics of nelfinavir and its active metabolite M8 in HIV-1-infected children

BACKGROUND

The objectives of this study are to develop and validate a population pharmacokinetic model that adequately describes the pharmacokinetics of nelfinavir and its active metabolite M8 in HIV-1-infected children; to define factors involved in the pharmacokinetic variability, which could aid in defining dosing strategies; and to correlate the pharmacokinetics to the treatment response.

METHODS

Protease inhibitor-naive, HIV-1-infected children were included. A population pharmacokinetic model of nelfinavir and M8 was developed using NONMEM. Bayesian analysis was used to estimate pharmacokinetic values. A pharmacokinetic-pharmacodynamic analysis was performed to study relationships between these values and the virologic response to therapy.

RESULTS

From 38 children, 724 nelfinavir and 636 M8 plasma concentrations were available. The pharmacokinetics of both compounds were described simultaneously with a one-compartment model with first-order elimination. Clearance (CL/F) and volume of distribution (V/F) were 32.6 L/h (interindividual variability [IIV]: 31.6%) and 281 L/h (IIV: 29.7%) for nelfinavir and 86.2 L/h (IIV: 43.1%) and 42.3 L/h for M8. No factors could be defined that affected the pharmacokinetics of nelfinavir or M8. The overall virologic response was 78% (HIV-1 RNA <500 copies/mL, on-treatment analysis). No differences in exposure to nelfinavir and M8 were observed between responders and nonresponders. The only factor distinguishing the two groups was a higher baseline HIV-1 RNA concentration in nonresponders.

CONCLUSION

A model was developed and validated that adequately described the population pharmacokinetics of nelfinavir and M8 in a childhood population. No factors affecting dosing strategies were identified, and no correlation could be demonstrated between the exposure to nelfinavir and M8 and the virologic treatment response.

Pharmacokinetics of antivirals in neonate

BACKGROUND

About 1000 neonates with HIV infection are born every day worldwide. The antiviral therapy for newborn infants is a real necessity. Pharmacokinetics is an important contribution to therapy and no review has been published on the pharmacokinetics of antivirals in neonates up to now.

AIMS

This article provides a review on the pharmacokinetics of antivirals in the neonate. The pharmacokinetic parameters in the neonate are compared with those of the adult, and when possible, the pharmacokinetic parameters were compared in neonates of different ages.

RESULTS

Zidovudine is the antiviral with the largest amount of information on its pharmacokinetics. The clearance (Cl; l/h/kg) of zidovudine is 0.15 (premature), 0.34 (1 day), 0.69 (7 days), 0.65 (< or =14 days), 1.14 (>14 days) and 1.56 (adult). t(1/2) (h) of zidovudine is 7.2 (premature), 4.2 (1 day), 4.0 (7 days), 3.1 (< or =14 days), 1.9 (>14 days) and 1.1 (adult). Zidovudine is mainly eliminated by conjugation with glucuronic acid and glucuronosyl transferase develops postnatally. Cl of lamivudine is 0.19 (1 day), 0.32 (7 days) and 0.30 (adult) and the Cl (l/h/m2) of didanosine is 65 (1 day) and 271 (7 days). A greater volume of distribution (Vd) has been observed in the neonate compared with the adult for nelfinavir, nevirapine and pleconaril.

CONCLUSIONS

The pharmacokinetic parameters of antivirals differ in the neonate and in the adult. The Cl is reduced and t(1/2) is increased in the neonate compared with the adult for zidovudine, lamivudine and ganciclovir. t(max) is generally greater in the neonate than in the adult due to reduced absorption rate in the neonate. The Vd of nelfinavir, nevirapine and pleconaril is greater in the newborn than in the adult. The neonate is a developing organism and the pharmacokinetic parameters of antivirals vary during the first weeks of life.

Pharmacotherapy of perinatal HIV

Continued spread of HIV infection among women has led to the use of antiretrovirals in pregnant women and their newborns. Regional strategies to prevent mother-to-child transmission are evolving. Altered drug disposition during pregnancy may require altered dosing or 'boosted' therapies to avoid treatment failure. Maturing drug elimination pathways in newborns must also be considered for effective therapy. Potential teratogenic effects and increased sensitivity to antiretroviral toxicities might be encountered in this population. Use of highly active antiretroviral therapy (HAART) to suppress viral replication combined with formula feeding can reduce the rate of mother-to-child HIV transmission to less than 2%. In resource-limited settings, less intensive regimens including zidovudine, lamivudine and nevirapine still substantially reduce mother-to-child transmission. Although difficult to perform, clinical trials to determine the safety, pharmacokinetics and optimal dosing of antiretroviral in pregnant women and their newborns are urgently needed.

Bayesian parameter estimates of nelfinavir and its active metabolite, hydroxy-tert-butylamide, in infants perinatally infected with human immunodeficiency virus type 1

The objective of the present study was to develop a population pharmacokinetic model for nelfinavir mesylate (NFV) and nelfinavir hydroxy-tert-butylamide (M8), the most abundant metabolite of NFV, in infants vertically infected with human immunodeficiency virus type 1 and participating in the Paediatric European Network for Treatment of AIDS 7 study. Plasma NFV concentrations were determined during repeated NFV administrations (two to three times a day). Eighteen infants younger that age 2 years participated in this study. The doses administered ranged from 71 to 203 mg/kg of body weight/day. Pharmacokinetic parameter estimates were obtained by a compartmental approach by using a kinetic model to simultaneously fit NFV and M8 (active metabolite) concentrations. M8 was shown to be formation rate limited and was characterized by first-order rate constants of formation and elimination. Body weight was found to be a more appropriate predictor than age of the changes in (i) the rate of metabolism, (ii) the elimination rate constant of NFV, and (iii) NFV clearance. Population parameters were computed to account for the relationship between the rate of metabolism and body weight. The estimated NFV and M8 elimination half-lives were 4.3 and 2.04 h, respectively. The estimated NFV clearance was 2.13 liters/h/kg. The M8 concentration-to-NFV concentration ratio was 0.64 +/- 0.44. In conclusion, the population pharmacokinetic model describing the dispositions of NFV and M8 should facilitate the design of future studies to elucidate the relative contributions of the parent compound and M8 to the pharmacological and toxic effects of NFV therapy.

Perinatal tuberculosis and HIV-1: considerations for resource-limited settings

Tuberculosis is the commonest HIV-1-related disease and the most frequent cause of mortality in young women in endemic regions. Tuberculosis and HIV-1 are independent risk factors for maternal mortality and adverse perinatal outcomes, and in combination have a greater impact on these parameters than their individual effects. In referral health centres in southern Africa around one-sixth of all maternal deaths are due to tuberculosis/HIV-1 coinfection. One-third (37%) of HIV-1-infected mothers with tuberculosis are severely immunocompromised, with CD4 counts of fewer than 200 cells/microL compared with 14-19% in mothers recruited into major mother-to-child intervention trials in Europe. Babies born to mothers with tuberculosis/HIV-1 also have higher rates of prematurity, low birthweight, and intrauterine growth restriction. Transmission rates of HIV-1 from mother to infant are around 25-45% in resource-limited settings, while that for mother-to-child-transmission of tuberculosis is 15% within 3 weeks of birth. We highlight this emergent problem, and discuss the dilemmas associated with diagnosis and management of pregnant HIV-1-infected mothers with tuberculosis, and their newborn babies.

Pharmacology considerations for antiretroviral therapy in human immunodeficiency virus (HIV)-infected children

The contemporary treatment of the child infected with human immunodeficiency virus (HIV) unavoidably requires combination therapy with antiretroviral agents and may include additional drugs for the prevention and treatment of opportunistic infections or other disease states. The current guidelines for the treatment of the HIV-infected child recommend that the same principles of treatment for adults should apply to children. However, the pharmacokinetic and pharmacodynamic characteristics of many agents and regimens used in adults have not been defined adequately in children, and large-scale clinical trials to establish safety and show efficacy have not been completed. Therefore, the clinician will be required to use agents with incomplete knowledge about their pharmacologic properties. The purpose of this article is to provide an overview of the pediatric pharmacologic principles, a review of the pharmacologic characteristics of selected antiretroviral agents in children, and a prospectus on the design of drug dosing regimens in children.