Abacavir dosing in neonates from birth to 3 months of life: a population pharmacokinetic modelling and simulation study

BACKGROUND

No evidence-based optimal dosing guidance is available for abacavir liquid formulation use from birth. We used abacavir pharmacokinetic data from neonates and infants to determine an exact abacavir dosing strategy (mg/kg) for infants aged 0-3 months and to propose dosing by WHO weight band for neonates.

METHODS

Abacavir pharmacokinetic and safety data were pooled from three completed studies (1997-2020): PACTG 321 (USA), the Tygerberg Cohort (South Africa), and IMPAACT P1106 (South Africa). PACTG 321 and the Tygerberg Cohort were performed in neonates exposed to HIV receiving a single dose of abacavir. IMPAACT P1106 included predominantly low birthweight (<2500 g) infants on antiretroviral therapy enrolled when they were younger than 3 months. We developed a population pharmacokinetic model and performed simulations to achieve abacavir exposures (area under the curve for 0-12 h) within the target range of 3·2-25·2 μg·h/mL, previously reported in older children.

FINDINGS

45 infants contributed 308 abacavir concentrations; 21 neonates were younger than 15 days. At first pharmacokinetic assessment, median postnatal age for PACTG 321 was 1 day and median bodyweight was 3·1 kg; for the Tygerberg Cohort it was 10 days and 3·3 kg; and for IMPAACT P1106 it was 73 days and 3·8 kg. Our model predicted a slow abacavir clearance of 2·51 mL/min per kg at birth, which doubled by 4 weeks of age. Therapeutic targets were achieved with exact abacavir doses of 2·0 mg/kg twice daily from 0 weeks to 4 weeks and 4·0 mg/kg twice daily from 4 weeks to 12 weeks. A fixed weight-band dosing strategy of 8 mg (for 2-3 kg), 10 mg (3-4 kg), and 12 mg (4-5 kg) abacavir twice daily achieved target exposures throughout the first 4 weeks of life without the need for dose adjustment due to age or bodyweight changes. No adverse events of grade 3 or higher were related to abacavir.

INTERPRETATION

Integration of these dosing strategies into national and international guidelines for the abacavir liquid formulation will expand antiretroviral options from birth and simplify the clinical management of neonates with HIV.

FUNDING

National Institute of Allergy and Infectious Diseases, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institute of Mental Health, and the Collaborative Initiative for Paediatric HIV Education and Research Programme.

Abacavir pharmacokinetics in African children living with HIV: A pooled analysis describing the effects of age, malnutrition and common concomitant medications

Aims

Abacavir is part of WHO‐recommended regimens to treat HIV in children under 15 years of age. In a pooled analysis across four studies, we describe abacavir population pharmacokinetics to investigate the influence of age, concomitant medications, malnutrition and formulation.

Methods

A total of 230 HIV‐infected African children were included, with median (range) age of 2.1 (0.1–12.8) years and weight of 9.8 (2.5–30.0) kg. The population pharmacokinetics of abacavir was described using nonlinear mixed‐effects modelling.

Results

Abacavir pharmacokinetics was best described by a two‐compartment model with first‐order elimination, and absorption described by transit compartments. Clearance was predicted around 54% of its mature value at birth and 90% at 10 months. The estimated typical clearance at steady state was 10.7 L/h in a child weighing 9.8 kg co‐treated with lopinavir/ritonavir, and was 12% higher in children receiving efavirenz. During coadministration of rifampicin‐based antituberculosis treatment and super‐boosted lopinavir in a 1:1 ratio with ritonavir, abacavir exposure decreased by 29.4%. Malnourished children living with HIV had higher abacavir exposure initially, but this effect waned with nutritional rehabilitation. An additional 18.4% reduction in clearance after the first abacavir dose was described, suggesting induction of clearance with time on lopinavir/ritonavir‐based therapy. Finally, absorption of the fixed dose combination tablet was 24% slower than the abacavir liquid formulation.

Conclusion

In this pooled analysis we found that children on lopinavir/ritonavir or efavirenz had similar abacavir exposures, while concomitant TB treatment and super‐boosted lopinavir gave significantly reduced abacavir concentrations.

Pharmacokinetic modelling of darunavir/ritonavir dose reduction (800/100 to 400/100 mg once daily) in a darunavir/ritonavir-containing regimen in virologically suppressed HIV-infected patients: ANRS 165 DARULIGHT sub-study

Background

In the ANRS 165 DARULIGHT study (NCT02384967) carried out in HIV-infected patients, the use of a darunavir/ritonavir-containing regimen with a switch to a reduced dose of darunavir maintained virological efficacy (≤50 copies/mL) for 48 weeks with a good safety profile.

Objectives

To assess the total and unbound blood plasma pharmacokinetics of darunavir and associated antiretrovirals, and their penetration into semen before and after dose reduction.

Patients and methods

Patients receiving a darunavir/ritonavir (800/100 mg q24h)-containing regimen for >6 months with plasma HIV-RNA ≤50 copies/mL for >12 months were switched to 400/100 mg darunavir/ritonavir q24h at week 0. A 24 h intensive pharmacokinetic blood sampling and a trough seminal sampling were performed before (week 0) and after (week 12) dose reduction. Individual pharmacokinetic parameter estimates were obtained using non-linear mixed-effect modelling for darunavir/ritonavir in blood plasma and used to test for bioequivalence, whereas darunavir/ritonavir in seminal plasma and NRTIs were analysed using a non-compartmental approach.

Results and conclusions

Fifteen patients completed the intensive pharmacokinetic analysis. There was no significant decrease in total and unbound darunavir blood plasma exposure despite a 50% decrease in darunavir daily dose from 800 to 400 mg (AUC0-24 = 65 563 versus 52 518 ng·h/mL; P = 0.25). A decrease in apparent oral clearance (CL/F) of both darunavir and ritonavir at week 12 suggests a modification of the initial darunavir/ritonavir daily dose balance (800/100 to 400/100 mg), in favour of a reduced inducer effect of darunavir on cytochrome P450 and efflux transporters compared with the standard dose.

A 10-year cohort analysis of routine paediatric ART data in a rural South African setting

South Africa's paediatric antiretroviral therapy (ART) programme is managed using a monitoring and evaluation tool known as TIER.Net. This electronic system has several advantages over paper-based systems, allowing profiling of the paediatric ART programme over time. We analysed anonymized TIER.Net data for HIV-infected children aged <15 years who had initiated ART in a rural district of South Africa between 2005 and 2014. We performed Kaplan–Meier survival analysis to assess outcomes over time. Records of 5461 children were available for analysis; 3593 (66%) children were retained in care. Losses from the programme were higher in children initiated on treatment in more recent years (P < 0·0001) and in children aged ≤1 year at treatment initiation (P < 0·0001). For children aged <3 years, abacavir was associated with a significantly higher rate of loss from the programme compared to stavudine (hazard ratio 1·9, P < 0·001). Viral load was suppressed in 48–52% of the cohort, with no significant change over the years (P = 0·398). Analysis of TIER.Net data over time provides enhanced insights into the performance of the paediatric ART programme and highlights interventions to improve programme performance.

Computational drug design strategies applied to the modelling of human immunodeficiency virus-1 reverse transcriptase inhibitors

Reverse transcriptase (RT) is a multifunctional enzyme in the human immunodeficiency virus (HIV)-1 life cycle and represents a primary target for drug discovery efforts against HIV-1 infection. Two classes of RT inhibitors, the nucleoside RT inhibitors (NRTIs) and the nonnucleoside transcriptase inhibitors are prominently used in the highly active antiretroviral therapy in combination with other anti-HIV drugs. However, the rapid emergence of drug-resistant viral strains has limited the successful rate of the anti-HIV agents. Computational methods are a significant part of the drug design process and indispensable to study drug resistance. In this review, recent advances in computer-aided drug design for the rational design of new compounds against HIV-1 RT using methods such as molecular docking, molecular dynamics, free energy calculations, quantitative structure-activity relationships, pharmacophore modelling and absorption, distribution, metabolism, excretion and toxicity prediction are discussed. Successful applications of these methodologies are also highlighted.

Drug resistance in non-B subtype HIV-1: impact of HIV-1 reverse transcriptase inhibitors

Human immunodeficiency virus (HIV) causes approximately 2.5 million new infections every year, and nearly 1.6 million patients succumb to HIV each year. Several factors, including cross-species transmission and error-prone replication have resulted in extraordinary genetic diversity of HIV groups. One of these groups, known as group M (main) contains nine subtypes (A-D, F-H and J-K) and causes ~95% of all HIV infections. Most reported data on susceptibility and resistance to anti-HIV therapies are from subtype B HIV infections, which are prevalent in developed countries but account for only ~12% of all global HIV infections, whereas non-B subtype HIV infections that account for ~88% of all HIV infections are prevalent primarily in low and middle-income countries. Although the treatments for subtype B infections are generally effective against non-B subtype infections, there are differences in response to therapies. Here, we review how polymorphisms, transmission efficiency of drug-resistant strains, and differences in genetic barrier for drug resistance can differentially alter the response to reverse transcriptase-targeting therapies in various subtypes.

Abacavir/lamivudine fixed-dose combination antiretroviral therapy for the treatment of HIV

In the past 15 years, improvements in the treatment of HIV infection have dramatically reduced morbidity and mortality. Nucleoside reverse transcriptase inhibitors are the backbone of combination antiretroviral therapy for the treatment of HIV. One of the recommended and commonly used therapies in this class is the once-daily fixed-dose combination of abacavir/lamivudine. Clinical studies and practice have shown these drugs to be potent, safe, and easy to use in a variety of settings; however, several recent reports have challenged the safety and efficacy claims among certain patient populations, including those at risk for cardiovascular disease and in those with high viral loads prior to treatment initiation. We reviewed abacavir/lamivudine as a treatment for HIV and discussed limitations of its use due to these controversial issues.