Pharmacokinetics of nelfinavir in human immunodeficiency virus-infected infants

Impact of Drug Treatment at Neonatal Ages on Variability of Drug Metabolism and Drug-drug Interactions in Adult Life

PURPOSE OF REVIEW

As the number of patients taking more than one medication concurrently continues to increase, predicting and preventing drug-drug interactions (DDIs) is now more important than ever. Administration of one drug can cause changes in the expression and activity of drug metabolizing enzymes (DMEs) and alter the efficacy or toxicity of other medications that are substrates for these enzymes, resulting in a DDI. In today's medical practice, potential DDIs are evaluated based on the current medications a patient is taking with little regard to drugs the patient has been exposed to in the past. The purpose of this review is to discuss potential impacts of drug treatment at neonatal ages on the variability of drug metabolism and DDIs in adult life.

RECENT FINDINGS

Existing evidence from the last thirty years has shown that exposure to certain xenobiotics during neonatal life has the potential to persistently alter DME expression through adult life. With recent advancements in the understanding of epigenetic regulation on gene expression, this phenomenon is resurfacing in the scientific community in hopes of defining possible mechanisms. Exposure to compounds that have the ability to bind nuclear receptors and trigger epigenetic modifications at neonatal and pediatric ages may have long-term, if not permanent, consequences on gene expression and DME activity.

SUMMARY

The information summarized in this review should challenge the way current healthcare providers assess DDI potential and may offer an explanation to the significant interindividual variability in drug metabolism that is observed among 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.

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.

Early initiation of lopinavir/ritonavir in infants less than 6 weeks of age: pharmacokinetics and 24-week safety and efficacy

BACKGROUND

With increasing recognition of the benefits of early antiretroviral therapy initiation in perinatally HIV-infected infants, data are needed regarding the pharmacokinetics (PK), safety, and efficacy of recommended first-line protease inhibitors such as lopinavir/ritonavir (LPV/r).

METHODS

A prospective, phase I/II, open-label, dose-finding trial evaluated LPV/r at a dose of 300/75 mg/m twice daily plus 2 nucleoside analogs in HIV-1-infected infants > or =14 days to <6 weeks of age. Intensive 12-hour PK evaluations were performed after 2 weeks of LPV/r therapy, and doses were modified to maintain LPV predose concentrations >1 microg/mL and area under the curve (AUC) <170 microg hr/mL.

RESULTS

Ten infants enrolled [median age 5.7 (range, 3.6-5.9) weeks] with median HIV-1 RNA of 6.0 (range, 4.7-7.2) log10 copies/mL; all completed 24 weeks of follow-up. Nine completed the intensive PK evaluation at a median LPV dose of 267 (range, 246-305) mg/m q12 hours; median measures were AUC = 36.6 (range, 27.9-62.6) microg hr/mL; predose concentration = 2.2 (range, 0.99-4.9) microg/mL; maximum concentration = 4.76 (range, 2.84-7.28) microg/mL and apparent clearance (L/h/m) = 6.75 (range, 2.79-12.83). Adverse events were limited to transient grade 3 neutropenia in 3 subjects. By week 24, 2 of 10 subjects had experienced a protocol-defined virologic failure.

CONCLUSIONS

Although the LPV AUC in this population was significantly lower than that observed in infants ages 6 weeks to 6 months, LPV/r-based antiretroviral therapy in doses of 300/75 mg/m BID was well tolerated and resulted in virologic control in 8 of 10 infants by 24 weeks. Additional investigation is needed to understand the long-term implications of the lower LPV exposure in this age group.

Pharmacokinetics, safety and efficacy of lopinavir/ritonavir in infants less than 6 months of age: 24 week results

OBJECTIVE

To investigate pharmacokinetics, safety and efficacy of lopinavir/ritonavir (LPV/r)-based therapy in HIV-1-infected infants 6 weeks to 6 months of age.

METHODS

A prospective, multicenter, open-label trial of 21 infants with HIV-1 RNA > 10 000 copies/ml and treated with LPV/r 300/75 mg/m twice daily plus two nucleoside reverse transcriptase inhibitors. Intensive pharmacokinetic sampling was performed at 2 weeks and predose concentrations were collected every 8 weeks; safety and plasma HIV-1 RNA were monitored every 4-12 weeks for 24 weeks.

RESULTS

Median age at enrollment was 14.7 weeks (range, 6.9-25.7) and 19/21 completed > or= 24 weeks of study. Although LPV/r apparent clearance was slightly higher than in older children, the median area under the concentration-time curve 0-12 h (67.5 mug.h/ml) was in the range reported from older children taking the recommended dose of 230/57.5 mg/m. Predose concentrations stabilized at a higher level after the first 2 weeks of study. In as-treated analysis at week 24, 10/19 (53%) had plasma HIV-1 RNA < 400 copies/ml (median change, -3.33 log10 copies/ml); poor adherence contributed to delayed viral suppression, which improved with longer follow-up. Three infants (14%) had transient adverse events of grade 3 or more that were possibly related to study treatment but did not require permanent treatment discontinuation.

CONCLUSION

Despite higher clearance in infants 6 weeks to 6 months of age, a twice daily dose of 300/75 mg/m LPV/r provided similar exposure to that in older children, was well tolerated and provided favorable virological and clinical efficacy.

Population pharmacokinetics of lamivudine in human immunodeficiency virus-exposed and -infected infants

This study aimed to determine lamivudine disposition in infants and to construct an appropriate dose adjustment for age, given the widespread use of lamivudine for both the prevention of mother-to-child transmission of human immunodeficiency virus (HIV) and the treatment of HIV-infected infants. Using a pooled-population approach, the pharmacokinetics of lamivudine in HIV-exposed or -infected infants from four Pediatric AIDS Clinical Trials Group studies were assessed. Ninety-nine infants provided 559 plasma samples for measurement of lamivudine concentrations. All infants received combination antiretroviral therapy including lamivudine dosed at 2 mg/kg of body weight every 12 h (q12h) for the first 4 to 6 weeks of life and at 4 mg/kg q12h thereafter. Lamivudine's apparent clearance was 0.25 liter/h/kg at birth, doubling by 28 days. In the final model, age and weight were the only significant covariates for lamivudine clearance. While lamivudine is predominantly renally eliminated, the serum creatinine level was not an independent covariate in the final model, possibly because it was confounded by age. Inclusion of interoccasion variability for bioavailability improved the individual subject clearance prediction over the age range studies. Simulations based on the final model predicted that by the age of 4 weeks, 90% of infant lamivudine concentrations with the standard 2 mg/kg dose of lamivudine fell below the adult median concentration. This population pharmacokinetic analysis affirms that adjusting the dose of lamivudine from 2 mg/kg to 4 mg/kg q12 h at the age of 4 weeks for infants with normal maturation of renal function will provide optimal lamivudine exposure, potentially contributing to more successful therapy.

A Computer-Based System to aid in the Interpretation of Plasma Concentrations of Antiretrovirals for Therapeutic Drug Monitoring

Objectives

To develop a computer-based system for modelling and interpreting plasma antiretroviral concentrations for therapeutic drug monitoring (TDM).

Methods

Data were extracted from a prospective TDM study of 199 HIV-infected patients (CCTG 578). Lopinavir (LPV) and efavirenz (EFV) pharmacokinetic (PK) parameters were modelled using a Bayesian method and interpreted by an expert committee of HIV specialists and pharmacologists who made TDM recommendations. These PK models and recommendations formed the knowledge base to develop an artificial intelligence (AI) system that could estimate drug exposure, interpret PK data and generate TDM recommendations. The modelled PK exposures and expert committee TDM recommendations were considered optimum and used to validate results obtained by the AI system.

Results

A group of patients, 67 on LPV, 46 on EFV and three on both drugs, were included in this analysis. Correlations were high for LPV and EFV estimated trough and 4 h post-dose concentrations between the AI estimates and modelled values (r>0.79 for all comparisons; P<0.0001). Although trough concentrations were similar, significant differences were seen for mean predicted 4 h concentrations for EFV (4.16 μg/ml versus 3.89 μg/ml; P=0.02) and LPV (7.99 μg/ml versus 8.79 μg/ml; P<0.001). The AI and expert committee TDM recommendations agreed in 53 out of 69 LPV cases [kappa (κ)=0.53; P<0.001] and 47 out of 49 EFV cases (κ=0.91; P<0.001).

Conclusions

The AI system successfully estimated LPV and EFV trough concentrations and achieved good agreement with expert committee TDM recommendations for EFV- and LPV-treated patients.

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.

Age-related effects on nelfinavir and M8 pharmacokinetics: a population study with 182 children

As a relationship between nelfinavir antiretroviral efficacy and plasma concentrations has been previously established, nelfinavir pharmacokinetics was investigated in order to optimize the individual treatment schedule in a pediatric population. A population pharmacokinetic model was developed to describe the concentration-time course of nelfinavir and its active metabolite M8. Individual characteristics were used to explain the large interindividual variability in children. Data from therapeutic drug monitoring in 182 children treated with nelfinavir were analyzed with NONMEM. Then Food and Drug Administration (FDA) current recommendations were evaluated estimating the percentage of children who reached the target minimum plasma concentration (0.8 mg/liter) by using Bayesian estimates. Nelfinavir pharmacokinetics was described by a one- compartment model with linear absorption and elimination. Pharmacokinetic estimates and the corresponding intersubject variabilities for the model were as follows: nelfinavir total clearance, 0.93 liters/h/kg (39%); volume of distribution, 6.9 liters/kg (109%); absorption rate, 0.5 h(-1); formation clearance fraction to hydroxy-tert-butylamide (M8), 0.025; M8 elimination rate, 1.88 h(-1) (49%). Apparent nelfinavir total clearance and volume of distribution decreased as a function of age. M8 elimination rate was increased by concomitant administration of nevirapine or efavirenz. Our data confirm that the FDA recommendations for children from 2 to 13 years are optimal and that the dose recommended for children younger than 2 years is adequate for the children from 2 months to 2 years old. However, in children younger than 2 months, the proposed nelfinavir newborn dose of 40 mg/kg of body weight twice daily is inadequate and we suggest increasing the dose to 50 to 60 mg/kg administered thrice daily. This assumption should be further evaluated.

Pharmacokinetics of nelfinavir and efavirenz in antiretroviral-naive, human immunodeficiency virus-infected subjects when administered alone or in combination with nucleoside analog reverse transcriptase inhibitors

Pharmacokinetic studies were conducted with human immunodeficiency virus-infected patients receiving efavirenz, nelfinavir, or both agents at weeks 4 and 32. Reductions of 25% and 45% were observed in the mean nelfinavir area under the concentration-time curve and minimum concentration of the drug in serum, and there was a 31% more rapid half-life for patients receiving both drugs compared to patients receiving nelfinavir alone. There were no significant differences in efavirenz pharmacokinetics.

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.

Therapeutic Drug Monitoring: Role for a Pharmacist in Multidisciplinary Antiretroviral Management

The current treatment guidelines for HIV pharmacotherapy recommend combinations of antiretrovirals (ARVs) to achieve optimal suppression of HIV replication. However, the initiation and long-term management of ARV therapy in a patient is often complicated by variable medication adherence, complex medication use with multiple drug interactions, the occurrence of drug toxicity, and drug therapy for comorbid conditions that require additional patient education and laboratory monitoring. For these reasons, the inclusion of a well-trained pharmacist in multidisciplinary health system management strategies has been increasing. Furthermore, the use of fixed-dose ARVs is accompanied by considerable interpatient variation in pharmacokinetics yielding a range of drug exposures from any given ARV dose. One approach to overcoming this variable drug exposure is to use plasma concentration monitoring (eg, therapeutic drug monitoring [TDM]) as a clinical tool to adjust doses to achieve targeted concentration ranges, often in conjunction with HIV resistance tests. While data in support of TDM are emerging, the development of programs that include an HIV pharmaceutical care specialist and an adherence program with an integrated clinical pharmacology resource that can provide reliable TDM assays has been reported and provides the rationale for including pharmacists in the implementation of ARV TDM programs.

Recomendaciones CEVIHP/SEIP/AEP/PNS respecto al tratamiento antirretroviral en niños y adolescentes infectados por el VIH

OBJECTIVE

To update antiretroviral recommendations in antiretroviral therapy (ART) in HIV-infected children and adolescents.

METHODS

Theses guidelines have been formulated by a panel of members of the Plan Nacional sobre el SIDA (PNS) and the Asociacion Espanola de Pediatria (AEP) by reviewing the current available evidence of efficacy, safety, and pharmacokinetics in pediatric studies. Three levels of evidence have been defined according to the source of data: Level A: randomized and controlled studies; Level B: Cohort and case-control studies; Level C: Descriptive studies and experts' opinion.

RESULTS

When to start ART should be made on an individual basis, discussed with the family, considering the risk of progression according to age, CD4 and viral load, the ART-related complications and adherence. The ART goal is to reach a maximum and durable viral suppression. This is not always possible, even with clinical and immunologic improvement. The difficulties of permanent adherence and side-effects are resulting in a more conservative trend to initiate ART, and to less toxic and simpler strategies. Currently, combinations of at least three drugs are of first choice both in acute and chronic infection. They must include 2 NA 1 1 NN or 2 NA 1 1 PI. ART is recommended in all symptomatic patients and, with few exceptions, in all infants in the first year of life. Older asymptomatic children should start ART according to CD4 count, especially CD4 percentage, that vary with age. Despite potent salvage therapies, it is common not to reach viral undetectability. Therapeutical options when ART fails are scarce due to cross-resistance. The cause of failure must be identified. Occasionally, there exists clinical and/or immunological progression, and a change of therapy with at least two new drugs still active for the patient, is warranted with the aim of increasing the CD4 count to a lower level of risk. Toxicity and adherence must be regularly monitored. Some aspects about post exposure prophylaxis and coinfection with HCV or HBV are discussed.

CONCLUSIONS

A higher level of evidence with regard to ART effectiveness and toxicity in pediatrics is currently available, leading to a more conservative and individualized approach. Clinical symptoms and CD4 count are the main determinants to start and change ART.

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.

Principles of antiretroviral treatment of children and adolescents with human immunodeficiency virus infection

Human immunodeficiency virus (HIV) infection requires life-long therapy to attain durable suppression of HIV replication and prevent or reverse HIV-related symptoms or immune system dysfunction. Combination therapy with 3 or more antiretroviral medications is currently widely recommended for treatment of children and adolescents with HIV infection. While potent regimens can initially reduce virus load to below assay quantitation limits in the majority of persons with HIV infection, 30% to 80% of children will have regimen failure and return of detectable plasma virus within 1 year. Adherence to therapy is critical to regimen success. Optimal treatment requires careful use of potent combinations of drugs, with attention to adherence, palatability, toxicity, and pharmacokinetics. Practitioners with experience caring for children and adolescents with HIV infection should be involved.

Pharmacokinetics of indinavir and nelfinavir in treatment-naive, human immunodeficiency virus-infected subjects

AIDS Clinical Trials Group protocol 388 was designed to compare a three-drug regimen (indinavir with dual nucleosides) to a four-drug regimen (indinavir plus nelfinavir or indinavir plus efavirenz with dual nucleosides). Blood samples from patients taking indinavir and nelfinavir were collected over 8 to 12 h following a specified dose and were analyzed with high-performance liquid chromatography. Pharmacokinetic data were derived by using noncompartmental analysis. Following administration of indinavir every 8 h in the absence of nelfinavir (n = 8), the median predose indinavir concentration (C(0)) was 369 ng/ml (range, <10 to 949 ng/ml; one subject had a concentration of <10 ng/ml), and the concentration 8 h after administration of the study dose was 159 ng/ml (range, 85 to 506 ng/ml). In the group receiving 1000 mg of indinavir every 12 h with nelfinavir (n = 10), the median indinavir C(0) was <10 ng/ml (range, <10 to 3740 ng/ml; six subjects had a value of <10 ng/ml), and the C(12 h) was 44 ng/ml (range, <10 to 4236 ng/ml; five subjects had a value of <10 ng/ml), while the subjects who received 1200 mg of indinavir every 12 h with nelfinavir (n = 7) had a C(0) of 146 ng/ml (range, 58 to 5215 ng/ml) and a C(12 h) of 95 ng/ml (range, 12 to 954 ng/ml). Indinavir clearance was significantly lower in the presence of nelfinavir (median [interquartile range], 34.1 liters/h [range, 22.6 to 45.8 liters/h] versus 47.9 liters/h [range, 42.7 to 70.3 liters/h]; P < 0.017). For subjects receiving 1,000 mg of indinavir every 12 h, the median C(0) value for nelfinavir (n = 9) was 1,779 ng/ml (range, <187.5 to 4579 ng/ml), and the C(12 h) was 1554 ng/ml (range, <187.5 to 5,540 ng/ml). Due to the unacceptable number of undetectable indinavir trough concentrations, 1200 mg of indinavir appears to be the preferred dose in a twice-daily regimen that includes nelfinavir.

Highly active antiretroviral therapy started in infants under 3 months of age: 72-week follow-up for CD4 cell count, viral load and drug resistance outcome

OBJECTIVE

To assess the feasibility and impact of highly active antiretroviral therapy (HAART) started in vertically HIV-1-infected infants less than 3 months of age.

DESIGN

A multicentre, phase I/II, non-randomized, open-label study (PENTA 7).

METHODS

Adverse events, plasma HIV-1 RNA, CD4 cell counts, CD4 cell percentage (CD4%) and clinical progression were recorded at baseline and prospectively to 72 weeks in order to assess the toxicity, tolerability and efficacy of a combination of stavudine, didanosine and nelfinavir. Selection of genotypic resistance was also investigated.

RESULTS

Twenty infants, of whom only three had Centers for Disease Control and Prevention stage B, initiated HAART at median age 2.5 months (range, 0.9-4.7) with median HIV-1 RNA concentration 5.5 log10 copies/ml (range, 3.2-6.8) and CD4% 33% (range, 11-66). Median follow-up was 96 weeks (range, 60-144). At week 72, 11 infants were still taking the original treatment. Few adverse events were reported related to treatment, all minor and causing treatment interruption in only three infants. No AIDS-defining events occurred; one child died of non-HIV-related causes (prematurity). All but two had CD4% > 25% at 72 weeks; however, 14 infants had virological failure and six acquired resistance mutations.

CONCLUSIONS

Early treatment with stavudine, didanosine and nelfinavir was well tolerated and associated with good clinical and immunological outcomes at week 72. However, a high rate of virological failure with emergence of genotypic resistance is of great concern. More palatable drug combinations for infants and closer drug monitoring are required.

Nelfinavir pharmacokinetics in stable human immunodeficiency virus-positive children: Pediatric AIDS Clinical Trials Group Protocol 377

OBJECTIVE

Pharmacokinetic data obtained from children who have human immunodeficiency virus (HIV) infection are essential for the safe and effective use of antiretroviral agents in pediatric populations. The objective of this study was to assess the impact of body weight on the pharmacokinetic disposition of nelfinavir (NFV) in the absence and presence of nevirapine (NVP) and compare the pharmacokinetic profiles of twice-daily (BID) and three-times-daily (TID) NFV regimens.

METHODS

This was an intensive pharmacokinetic substudy nested in a phase II, multicenter, randomized, open-label trial. Forty-five HIV-infected children receiving NFV 30 mg/kg TID and 6 HIV-infected children receiving NFV 55 mg/kg BID were enrolled in this study and assigned to 1 of 4 stavudine-containing regimens, 3 containing NFV and 2 containing NVP. Area under the plasma concentration-time curves from 0 to 8 hours (AUC(0-8 hours)) and from 0 to 12 hours (AUC(0-12 hours)) for the TID and BID regimens, respectively, were determined. For comparative purposes, the AUC(0-24 hours) was also calculated for each regimen.

RESULTS

NFV exposure in the absence of NVP was decreased in children who were <25 kg compared with those who were >25 kg (a 2.6-fold difference in median AUC(0-8 hours)). NFV pharmacokinetics in the presence of NVP did not differ between the <25 kg and >25 kg groups. The AUC(0-24 hours) for children who were <30 kg and on NFV BID was comparable to the AUC(0-24 hours) for children who were >25 kg and on NFV TID but was 2.7-fold greater than AUC(0-24 hours) for children who were <25 kg and on NFV TID.

CONCLUSIONS

NFV in the absence of NVP resulted in less than half the drug exposure in children who were <25 kg compared with children who were >25 kg. NFV dosed at 55 mg/kg BID in children who are <30 kg provides comparable exposure to that measured in children who are >25 kg and receiving NFV 30 mg/kg TID.

Pharmacokinetics and pharmacodynamics of nelfinavir administered twice or thrice daily to human immunodeficiency virus type 1-infected children

We studied the pharmacokinetics and pharmacodynamics of nelfinavir administered 2 or 3 times per day to human immunodeficiency virus type 1 (HIV-1)-infected children receiving highly active antiretroviral therapy containing nelfinavir. The geometric mean trough concentrations of nelfinavir for the thrice- and twice-daily regimens were 1.55 mg/L and 1.11 mg/L, respectively (P=not significant). Nelfinavir concentrations did not correlate with total daily dose, dose per kilogram of weight, age, weight, previous protease inhibitor (PI) experience, or CD4(+) cell percentage. In the 25 PI-naive children, the virus load reductions at 24 weeks of treatment with the twice- and thrice-daily regimens were comparable. A significantly higher percentage of children in the twice-daily group had a trough concentration of nelfinavir of less than the inhibitory concentration of 95% (P=.042). The decrease in the virus load at 24 weeks of treatment was not correlated with the trough concentration of nelfinavir. The variability of trough concentrations was extremely high, particularly among recipients of the twice-daily regimen, resulting in a higher number of patients with subinhibitory concentrations of nelfinavir in this group.

Ritonavir-enhanced pharmacokinetics of nelfinavir/M8 during rifampin use

OBJECTIVE

To describe a case of successful protease inhibitor-based highly active antiretroviral therapy (HAART) concomitant with rifampin.

CASE SUMMARY

In a 7-month-old male infant with tuberculosis and HIV-1 infection, tuberculosis therapy including rifampin and HAART containing the protease inhibitor nelfinavir 40 mg/kg every 8 hours was started. Intensive steady-state pharmacokinetic sampling from baseline to 8 hours revealed very low plasma concentrations of nelfinavir: area under the plasma concentration-time curve (AUC(0-24)) <10% of adult population values for 750 mg every 8 hours and nonquantifiable concentrations of nelfinavir's principal metabolite (M8). Nelfinavir 40 mg/kg every 8 hours was then substituted with nelfinavir 30 mg/kg twice daily plus ritonavir 400 mg/m(2) twice daily. Intensive steady-state (0-12 h) pharmacokinetic sampling was repeated. Nelfinavir concentrations had improved, but remained low when compared with adult population values of 1250 mg every 12 hours: AUC(0-24) 21.9 versus 47.6 mg/L*h (46%) and 12-hour trough level (C(12)) 0.25 versus 0.85 mg/L (29%). However, concentrations of M8 considerably exceeded population values: AUC(0-24) 57.5 versus 13.6 mg/L*h (443%) and C(12) 1.35 versus 0.28 mg/L (482%). Since M8 concentrations were highly elevated, pharmacokinetic parameters for (nelfinavir + M8) were used rather than those for nelfinavir alone. Thus, AUC(0-24) (nelfinavir + M8) and C(12) (nelfinavir + M8) comprised 130% and 142%, respectively of the adult population values. This, in addition to good clinical response and tolerability, favored continuation of the regimen.

CONCLUSIONS

In an infant, nelfinavir-containing HAART was successfully used with rifampin after the addition of ritonavir. Ritonavir resolved the pharmacokinetic interaction between rifampin and nelfinavir by boosting nelfinavir and, especially, M8 concentrations. More research is needed to confirm these results.

The role of protease inhibitor therapy in children with HIV infection

In comparison with HIV infection in adults, higher HIV RNA levels in children with perinatal HIV infection, differences in the natural history of HIV disease progression, and the presence of a relatively immature immune system contribute to the more complex and problematic nature of pediatric antiretroviral therapy. Current US treatment guidelines for pediatric HIV infection advocate aggressive therapy with potent combination antiretroviral regimens, to achieve profound and durable suppression of viral replication and preservation of immune function. The combination of a protease inhibitor (PI) and dual nucleoside reverse transcriptase inhibitors (NRTIs) is the most commonly recommended form of highly active antiretroviral treatment (HAART). However, use of PI therapy in pediatrics has been constrained by the lack of suitable drug formulations, a paucity of pharmacokinetic and safety data, and drug intolerance. Pharmacokinetic studies of PIs demonstrate frequent differences between children and adults, and greater variability among children, which has led to subtherapeutic dosage regimens and the development of viral resistance. The optimal dosage of many PIs in younger children is not yet known. A therapeutically important drug interaction associated with PIs is that occurring between the various PIs themselves, which allows lower doses of PI at less frequent intervals. Dual PI regimens will probably become more common, as they permit a simpler antiretroviral regimen, lower pill/medication burden, fewer adverse effects and improved adherence. Poor adherence to antiretroviral therapy remains the greatest barrier to overall success in the treatment of HIV-infected children. The key to improving adherence in HIV-infected children is to find treatment regimens that are better suited to their normal life. With improvements in existing PIs and the development of newer ones, simplification of current antiretroviral therapy to once-daily regimens without loss of potency should be achievable. PI-containing HAART has transformed HIV infection into a chronic illness, and HIV-infected children now live longer.

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

BACKGROUND

In children younger than 2 years of age vertically infected with HIV-1, the recommended pediatric dosing regimen for nelfinavir (20 to 30 mg/kg three times a day) provides insufficient drug exposure. This study was conducted to determine the steady state pharmacokinetics of nelfinavir and its active metabolite, M8, in this population.

METHODS

Fourteen infants (2.3 to 8.5 months) underwent 18 intensive pharmacokinetic studies of nelfinavir and M8 at steady state. Nelfinavir and M8 concentrations were measured by high performance liquid chromatography coupled with mass spectrometry, and individual pharmacokinetic values were determined.

RESULTS

A mean nelfinavir daily dose of 135.7 +/- 18.8 mg/kg (twice or three times a day) resulted in median C(min), C(max), area under the plasma concentration-time curve (AUC(0-24 h)) and CL/ for nelfinavir of 0.627 mg/l, 2.39 mg/l, 30.6 mg*h/l and 4.2 liters/h/kg, respectively. When normalized for a daily dose of nelfinavir of 150 mg/kg/day, 16.7% of C(max) and 27.8% of AUC(0-24 h) values were below the tenth percentile for adult values.

CONCLUSIONS

During the first year of life, nelfinavir requirement is much higher than in older children and adults to obtain similar drug exposure. The mechanisms underlying such differences may involve higher first past metabolism and/or drug interactions or might be related to feeding conditions.

Efavirenz liquid formulation in human immunodeficiency virus-infected children

BACKGROUND

This study determined the safety, pharmacokinetics, antiviral activity and immunologic effects of efavirenz liquid formulation, nelfinavir and nucleoside reverse transcriptase inhibitors (NRTIs) in HIV-infected children, 3 to 9 years of age.

METHODS

Plasma HIV-1 RNA and lymphocyte subsets were measured at various intervals after initiation of therapy. Pharmacokinetic studies were performed at Week 2, and doses of efavirenz and nelfinavir were adjusted if area under the curve values fell outside specified target ranges.

RESULTS

This combination of antiretrovirals was well-tolerated. Pharmacokinetic values were similar to those observed in a previous study of older children who received efavirenz capsules in combination with nelfinavir and NRTIs. After 48 weeks of therapy 63% of subjects had plasma HIV RNA levels of <400 copies/ml, and 58% had <50 copies/ml in an intent-to-treat analysis. CD4 cell count and percentage rose significantly over this time, whereas the number of activated CD8 cells declined.

CONCLUSIONS

Combination therapy with efavirenz liquid formulation, nelfinavir and NRTIs is an attractive treatment option for HIV-infected children >3 years of age who are unable to take efavirenz capsules.

Early multitherapy including a protease inhibitor for human immunodeficiency virus type 1-infected infants

BACKGROUND

To assess tolerance and efficacy of early multitherapy including a protease inhibitor for infants perinatally infected with HIV.

METHODS

Observational study of tolerance and clinical and immunovirologic evolution in HIV-infected infants treated before the age of 1 year in the French Perinatal Study.

RESULTS

Thirty-one infants were included. The median age was 3.7 months at initiation of multitherapy. Clinical stage was C (n = 8), B (n = 5) or A/N (n = 18). The median HIV RNA viral load was 5.8 log copies/ml, and the median CD4 cell percentage was 29%. Median follow-up of treatment was 27 months. Of 31 infants 15 experienced mild to moderate adverse events. No infant had clinical or immunologic progression. The median change in viral load was -2.7 log copies/ml after 3 months, -2.0 log after 12 months and -1.7 log after 24 months of treatment. The proportion of infants with a viral load below 500 copies/ml decreased from 53% at 6 months to 18% at 24 months of treatment. The virologic response was not correlated with viral load at baseline. However, the slope of the viral load decrease during the first month of treatment was predictive of the virologic response at 3 and 6 months. Fourteen infants with a viral load of >500 copies/ml after 6 months of treatment displayed viruses with antiretroviral resistance mutations in reverse transcriptase and/or protease genes.

CONCLUSIONS

Despite the absence of clinical or immunologic progression, the high frequency of virologic failure associated with genotypic resistance reveals the difficulties associated with implementing antiretroviral multitherapy in infants. Suboptimal doses of protease inhibitor could be a factor contributing to treatment failure.

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

The pharmacokinetics of nelfinavir (NFV) in neonates younger than 4 weeks of age was assessed. Three cohorts of HIV-exposed neonates were enrolled in cohorts to receive 15, 30, and 45 mg of NFV/kg twice daily in combination with stavudine and didanosine for 4 weeks after birth. Trough NFV concentrations (C(min)) were measured at 1 and 7 days of age. Intensive pharmacokinetic evaluations were performed at 14 and 28 days of age. The median NFV C(min) values in the 15 mg/kg (6 patients), 30 mg/kg (5), and 45 mg/kg (11) cohorts at 1, 7, 14, and 28 days of age were 0.19, 1.21, 0.51, and 0.33; 1.02, 3.18, 0.73, and 0.55; and 0.67, 3.21, 0.70, and 0.73 mg/L, respectively. The median area under the plasma concentration-versus-time curve values over 12 hours in the three cohorts at 14 and 28 days of age were 14.4 and 8.7, 19.4 and 15.8, and 23.4 and 18.5 (h. mg)/L, respectively. No serious adverse events were observed. In conclusion, the systemic exposure of NFV decreased after 7 days of age, possibly because of hepatic enzyme maturation, autoinduction of NFV metabolism, and/or changes in NFV absorption. The highly variable systemic exposure observed in the study indicates that therapeutic drug monitoring seems warranted to ensure adequate NFV dosing in this population.

Pharmacokinetics of Nelfinavir in Children: Influencing Factors and dose Implications

Objectives

The study describes the pharmacokinetics (PK) of the protease inhibitor nelfinavir and its active metabolite M8 in children and evaluates the influence of patient-related factors on nelfinavir plasma levels.

Methods

HIV-1-infected children treated with nelfinavir every 8 h (q8h) were eligible for inclusion in this retrospective study. 0–8 h intensive plasma pharmacokinetics (PK) sampling was performed at steady state. Nelfinavir maximum concentration (Cmax), area under the plasma concentration-time curve in 0–8 h (AUC0-8), trough level at the 8 h time point (C8) and relative apparent oral clearance (Cl*F/kg) were calculated.

Results

Twenty-four children (median age: 4.5 years, median nelfinavir dose: 28 mg/kg q8h) were included. Nelfinavir PK were highly variable: 10/24 children had an AUC0-8 below the value of 12.5 mg/l*h, which has previously been associated with an increased virological failure rate in children. With children aged <2 years and a dose of 20 mg/kg q8h, a non-significant trend was observed to more AUC0-8<12.5 mg/l*h [odds ratio (OR) (95% CI): 2.44 (0.41–14.7) and 8.7 (0.79–95), respectively]. Nelfinavir C8 correlated strongly with AUC0-8 (r=0.89, P<0.001). C8 >0.69 mg/l predicted an AUC0-8 >12.5 mg/l*h with 71% sensitivity and 80% specificity. Dose of nelfinavir per body surface area was a better predictor of AUC0-8 than dose per body weight.

Conclusion

Nelfinavir PK show high interindividual variability in children. Children <2 years old tend to be at increased risk for low nelfinavir levels. These data show that the nelfinavir dose of 20 mg/kg q8h is inadequate in most children. Also, these data suggest that paediatric dosing of nelfinavir based on body surface area should be considered. Therapeutic drug monitoring (TDM) can detect abnormal plasma levels and is therefore useful in optimizing nelfinavir therapy in HIV-infected children. However, further research is needed to more firmly establish a therapeutic range for nelfinavir in children.