Attaining Equity of Access to Research: Perspective on Research in Pregnancy and Breastfeeding Following Dolores Shockley Lecture at ASCPT2024.

Everybody deserves access to evidence-based information to make decisions about their health. However, in many situations, clinical trial eligibility criteria mean that specific data do not exist for certain groups of individuals. These include pregnant and breastfeeding women, children, older people, those with hepatic and renal dysfunction, those with acute severe illness, and those with multiple co-morbidities and interacting medications. Resultantly, there may not be specific drug-dosing information for many patients who are treated in a clinical setting. The ASCPT2024 Dolores Shockley Lecture focused on the equitable access to research with a specific focus on clinical pharmacology studies in pregnancy and breastfeeding. To ensure the safe, effective use of medication in pregnancy and breastfeeding, women should be included in clinical trials and pharmacokinetic studies when a medication is anticipated to be used in women of childbearing potential. Community groups should be involved at all stages of research to maintain transparency and trust. This ensures that local priorities are investigated, that communities understand the findings and are empowered to make evidence-based decisions about their own medication use. Principles informing the design of such studies in pregnancy and lactation are in existence. Mathematical techniques such as physiologically-based pharmacokinetic modeling and stochastic simulation and estimation can enhance study design, and population pharmacokinetic modeling be used to understand variability within and between individuals. Data should be made findable, accessible, interoperable, and reusable (FAIR). Information (and where necessary, training) regarding the use of these approaches should be provided to decision-making stakeholders such as ethics committees and regulatory bodies.

Determinants of early change in serum creatinine after initiation of dolutegravir-based antiretroviral therapy in South Africa.

AIMS: Dolutegravir increases serum creatinine by inhibiting its renal tubular secretion and elimination. We investigated determinants of early changes in serum creatinine in a southern African cohort starting first-line dolutegravir-based antiretroviral therapy (ART). METHODS: We conducted a secondary analysis of data from participants in a randomized controlled trial of dolutegravir, emtricitabine and tenofovir disoproxil fumarate (TDF) or tenofovir alafenamide fumarate (TAF) (ADVANCE, NCT03122262). We assessed clinical, pharmacokinetic and genetic factors associated with change in serum creatinine from baseline to Week 4 using linear regression models adjusted for age, sex, baseline serum creatinine, HIV-1 RNA concentration, CD4 T-cell count, total body weight and co-trimoxazole use. RESULTS: We included 689 participants, of whom 470 had pharmacokinetic data and 315 had genetic data. Mean change in serum creatinine was 11.3 (SD 9.9) µmol.L-1. Factors that were positively associated with change in serum creatinine at Week 4 were increased log dolutegravir area under the 24-h concentration-time curve (change in creatinine coefficient [ß] = 2.78 µmol.L-1 [95% confidence interval (CI) 0.54, 5.01]), TDF use (ß = 2.30 [0.53, 4.06]), male sex (ß = 5.20 [2.92, 7.48]), baseline serum creatinine (ß = -0.22 [-0.31, -0.12]) and UGT1A1 rs929596 A→G polymorphism with a dominant model (ß = -2.33 [-4.49, -0.17]). The latter did not withstand correction for multiple testing. CONCLUSIONS: Multiple clinical and pharmacokinetic factors were associated with early change in serum creatinine in individuals initiating dolutegravir-based ART. UGT1A1 polymorphisms may play a role, but further research on genetic determinants is needed.

A systematic review on maternal-to-infant transfer of drugs through breast milk during the treatment of malaria, tuberculosis, and neglected tropical diseases.

BACKGROUND: Exclusive breastfeeding of infants under 6 months of age is recommended by the World Health Organization. In 2021, over 300 million combined incident cases of malaria, tuberculosis, and neglected tropical diseases (NTDs) were reported, predominantly in low-income countries. For many of the drugs used as first-line treatments for these conditions, there is limited knowledge on infant exposure through breastfeeding with poorly understood consequences. This review summarized available knowledge on mother-to-infant transfer of these drugs to inform future lactation pharmacokinetic studies. METHODOLOGY: A list of first-line drugs was generated from the latest WHO treatment guidelines. Using standard online databases, 2 independent reviewers searched for eligible articles reporting lactation pharmacokinetics studies and extracted information on study design, participant characteristics, and the mathematical approach used for parameter estimation. A third reviewer settled any disagreements between the 2 reviewers. All studies were scored against the standardized "ClinPK" checklist for conformity to best practices for reporting clinical pharmacokinetic studies. Simple proportions were used to summarize different study characteristics. FINDINGS: The most remarkable finding was the scarcity of lactation pharmacokinetic data. Only 15 of the 69 drugs we listed had lactation pharmacokinetics fully characterized. Most studies enrolled few mothers, and only one evaluated infant drug concentrations. Up to 66% of the studies used non-compartmental analysis to estimate pharmacokinetic parameters rather than model-based compartmental analysis. Unlike non-compartmental approaches, model-based compartmental analysis provides for dynamic characterization of individual plasma and breast milk concentration-time profiles and adequately characterizes variability within and between individuals, using sparsely sampled data. The "ClinPK" checklist inadequately appraised the studies with variability in the number of relevant criteria across different studies. CONCLUSIONS/SIGNIFICANCE: A consensus is required on best practices for conducting and reporting lactation pharmacokinetic studies, especially in neglected diseases such as malaria, tuberculosis, and NTDs, to optimize treatment of mother-infant pairs.

Pharmacogenetics of tenofovir clearance among Southern Africans living with HIV.

BACKGROUND: Tenofovir is a component of preferred combination antiretroviral therapy (ART) regimens in Africa. Few pharmacogenetic studies have been conducted on tenofovir exposure in Africa, where genetic diversity is greatest. OBJECTIVE: We characterized the pharmacogenetics of plasma tenofovir clearance in Southern Africans receiving tenofovir disoproxil fumarate (TDF) or tenofovir alafenamide (TAF). METHODS: Adults randomized to TAF or TDF in dolutegravir-containing arms of the ADVANCE trial (NCT03122262) were studied. Linear regression models stratified by study arm examined associations with unexplained variability in tenofovir clearance. We investigated genetic associations with polymorphisms selected a priori followed by genome-wide associations. RESULTS: A total of 268 participants (138 and 130 in the TAF and TDF arm, respectively) were evaluable for associations. Among polymorphisms previously associated with any drug-related phenotype, IFNL4 rs12979860 was associated with more rapid tenofovir clearance in both arms (TAF: P = 0.003; TDF: P = 0.003). Genome-wide, the lowest P values for tenofovir clearance in TAF and TDF arms were LINC01684 rs9305223 (P = 3.0 × 10-8) and intergenic rs142693425 (P = 1.4 × 10-8), respectively. CONCLUSION: Among Southern Africans randomized to TAF or TDF in ADVANCE, unexplained variability in tenofovir clearance was associated with a polymorphism in IFNL4, an immune-response gene. It is unclear how this gene would affect tenofovir disposition.

Population pharmacokinetics of tenofovir given as either tenofovir disoproxil fumarate or tenofovir alafenamide in an African population.

Tenofovir disoproxil fumarate (TDF) and tenofovir alafenamide (TAF) are prodrugs of the nucleotide analogue tenofovir, which acts intracellularly to inhibit HIV replication. Whereas TDF converts to tenofovir in plasma and may cause kidney and bone toxicity, TAF mostly converts to tenofovir intracellularly, so it can be administered at lower doses. TAF leads to lower tenofovir plasma concentrations and lower toxicity, but there are limited data on its use in Africa. We used data from 41 South African adults living with HIV from the ADVANCE trial and described, with a joint model, the population pharmacokinetics of tenofovir given as TAF or TDF. The TDF was modeled to appear in plasma as tenofovir with a simple first-order process. Instead, two parallel pathways were used for a TAF dose: an estimated 32.4% quickly appeared as tenofovir into the systemic circulation with first-order absorption, whereas the rest was sequestered intracellularly and released into the systemic circulation as tenofovir slowly. Once in plasma (from either TAF or TDF), tenofovir disposition followed two-compartment kinetics and had a clearance of 44.7 L/h (40.2-49.5), for a typical 70-kg individual. This semimechanistic model describes the population pharmacokinetics of tenofovir when dosed as either TDF or TAF in an African population living with HIV and can be used as a tool for exposure prediction in patients, and to simulate alternative regimes to inform further clinical trials.

Drug-drug interaction between rifabutin and dolutegravir: A population pharmacokinetic model.

Rifampicin, a potent enzyme inducer, causes marked reduction of dolutegravir exposure. Rifabutin, a less potent enzyme inducer, may offer an alternative to rifampicin. We aimed to characterize the population pharmacokinetics of dolutegravir when co-administered with rifabutin. We extended an existing dolutegravir model to include data from volunteers co-administered with dolutegravir 50 mg and rifabutin 300 mg once daily. We ran simulations of dolutegravir with and without rifabutin co-administration and compare dolutegravir trough concentrations with the IC90 and EC90 of 0.064 and 0.3 mg/L, respectively. Rifabutin decreased dolutegravir's volume of distribution by 33.1% (95% confidence interval 25.1%-42.3%) but did not affect the area under the concentration-time curve. Simulations showed that when 50 mg dolutegravir is co-administered with rifabutin once daily, the probability to attain trough concentrations above the IC90 of 0.064 mg/L is more than 99%. Therefore, there is no need for dolutegravir dose adjustment. Rifabutin may offer an alternative to rifampicin for the treatment of HIV/tuberculosis co-infected individuals.

Pharmacogenetics of Dolutegravir Plasma Exposure Among Southern Africans With Human Immunodeficiency Virus.

BACKGROUND: Dolutegravir is a component of preferred antiretroviral therapy (ART) regimens. We characterized the pharmacogenetics of dolutegravir exposure after ART initiation in the ADVANCE trial in South Africa. METHODS: Genome-wide genotyping followed by imputation was performed. We developed a population pharmacokinetic model for dolutegravir using nonlinear mixed-effects modeling. Linear regression models examined associations with unexplained variability in dolutegravir area under the concentration-time curve (AUCVAR). RESULTS: Genetic associations were evaluable in 284 individuals. Of 9 polymorphisms previously associated with dolutegravir pharmacokinetics, the lowest P value with AUCVAR was UGT1A1 rs887829 (P = 1.8 × 10-4), which was also associated with log10 bilirubin (P = 8.6 × 10-13). After adjusting for rs887829, AUCVAR was independently associated with rs28899168 in the UGT1A locus (P = .02), as were bilirubin concentrations (P = 7.7 × 10-8). In the population pharmacokinetic model, rs887829 T/T and C/T were associated with 25.9% and 10.8% decreases in dolutegravir clearance, respectively, compared with C/C. The lowest P value for AUCVAR genome-wide was CAMKMT rs343942 (P = 2.4 × 10-7). CONCLUSIONS: In South Africa, rs887829 and rs28899168 in the UGT1A locus were independently associated with dolutegravir AUCVAR. The novel rs28899168 association warrants replication. This study enhances understanding of dolutegravir pharmacogenetics in Africa.

Population Pharmacokinetic Model and Alternative Dosing Regimens for Dolutegravir Coadministered with Rifampicin.

Dolutegravir-based regimens are recommended as first-line therapy for HIV in low- and middle-income countries where tuberculosis is the most common opportunistic infection. Concurrent HIV/tuberculosis treatment is challenging because of drug-drug interactions. Our analysis aimed to characterize dolutegravir's population pharmacokinetics when coadministered with rifampicin and assess alternative dolutegravir dosing regimens. We developed a population pharmacokinetic model of dolutegravir in NONMEM with data from two healthy-volunteer studies (RADIO and ClinicalTrials.gov identifier NCT01231542) and validated it with data from the INSPIRING study, which consisted of participants living with HIV. The model was developed with 817 dolutegravir plasma concentrations from 41 participants. A 2-compartment model with first-order elimination and lagged absorption best described dolutegravir's pharmacokinetics. For a typical 70-kg individual, we estimated a clearance, absorption rate constant, central volume, and peripheral volume of 1.03 L/h, 1.61 h-1, 12.7 L, and 3.85 L, respectively. Rifampicin coadministration increased dolutegravir clearance by 144% (95% confidence interval [CI], 126 to 161%). Simulations showed that when 50 or 100 mg once-daily dolutegravir is coadministered with rifampicin in 70-kg individuals, 71.7% and 91.5% attain trough concentrations above 0.064 mg/L, the protein-adjusted 90% inhibitory concentration (PA-IC90), respectively. The model developed from healthy-volunteer data describes patient data reasonably well but underpredicts trough concentrations. Although 50 mg of dolutegravir given twice daily achieves target concentrations in more than 99% of individuals cotreated with rifampicin, 100 mg of dolutegravir, once daily, in the same population is predicted to achieve satisfactory pharmacokinetic target attainment. The efficacy of this regimen should be investigated since it presents an opportunity for treatment simplification.

Concentration-response relationships of dolutegravir and efavirenz with weight change after starting antiretroviral therapy.

Dolutegravir is associated with more weight gain than efavirenz in people starting antiretroviral therapy (ART). We investigated the concentration-response relationships of efavirenz and dolutegravir with weight gain. We determined concentration-response relationships of dolutegravir and efavirenz (both combined with tenofovir disoproxil fumarate and emtricitabine) with changes in weight and fat distribution, derived from dual-energy x-ray absorptiometry scans, in a nested study of ART-naïve participants from a randomised controlled trial. Pharmacokinetic parameters used in analyses were efavirenz mid-dosing interval concentrations and estimated dolutegravir area under the concentration-time curve using a population pharmacokinetic model developed in the study population. Study outcomes were percentage changes from baseline to week 48 in weight, and visceral and subcutaneous adipose tissue mass. Pharmacokinetic data were available for 158 and 233 participants in the efavirenz arm and dolutegravir arms respectively; 57.0% were women. On multivariable linear regression there were independent negative associations between efavirenz concentrations and changes in both weight (P < .001) and subcutaneous adipose tissue mass (P = .002). Estimated dolutegravir area under the concentration-time curve up to 24 hours was not associated with change in weight (P = .109) but was negatively associated with change in visceral adipose tissue mass (P = .025). We found an independent negative concentration-response relationship between efavirenz concentrations and weight change in ART-naïve participants. Dolutegravir concentrations were not independently associated with weight change. These findings suggest that weight gain differences between efavirenz and dolutegravir are driven by efavirenz toxicity impairing weight gain rather than by off-target effects of dolutegravir causing weight gain.

Dolutegravir pharmacokinetics during co-administration with either artemether/lumefantrine or artesunate/amodiaquine.

BACKGROUND: In sub-Saharan Africa, artemisinin-containing therapies for malaria treatment are regularly co-administered with ART. Currently, dolutegravir-based regimens are recommended as first-line therapy for HIV across most of Africa. OBJECTIVES: To investigate the population pharmacokinetics of dolutegravir during co-administration with artemether/lumefantrine or artesunate/amodiaquine, two commonly used antimalarial therapies. METHODS: We developed a population pharmacokinetic model of dolutegravir with data from 26 healthy volunteers in two Phase 2 studies with a total of 403 dolutegravir plasma concentrations at steady state. Volunteers received 50 mg of dolutegravir once daily alone or in combination with standard treatment doses of artemether/lumefantrine (80/480 mg) or artesunate/amodiaquine (200/540 mg). RESULTS: A two-compartment model with first-order elimination and transit compartment absorption best described the concentration-time data of dolutegravir. Typical population estimates for clearance, absorption rate constant, central volume, peripheral volume and mean absorption transit time were 0.713 L/h, 1.68 h-1, 13.2 L, 5.73 L and 1.18 h, respectively. Co-administration of artemether/lumefantrine or artesunate/amodiaquine increased dolutegravir clearance by 10.6% (95% CI 4.09%-34.5%) and 26.4% (95% CI 14.3%-51.4%), respectively. Simulations showed that simulated trough concentrations of dolutegravir alone or in combination with artemether/lumefantrine or artesunate/amodiaquine are maintained above the dolutegravir protein-adjusted IC90 of 0.064 mg/L for more than 99% of the individuals. CONCLUSIONS: Dolutegravir dose adjustments are not necessary for patients who are taking standard 3 day treatment doses of artemether/lumefantrine or artesunate/amodiaquine.