Background Dolutegravir is a component of preferred antiretroviral therapy (ART) regimens. We characterised the pharmacogenetics of dolutegravir exposure following 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 non-linear mixed-effects modelling. 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 nine 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 = 0.02), 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 to 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.

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-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.

BACKGROUND: Pharmacokinetic variability arising from drug-drug interactions and pharmacogenetics may influence the effectiveness of treatment regimens for TB. The Improving Treatment Success Trial compared the WHO-recommended standard treatment in TB patients with an experimental regimen substituting ethambutol with moxifloxacin (MFX) in Durban, South Africa.METHODS: Non-linear mixed-effects modelling was used to investigate the population pharmacokinetics of rifampicin (RIF), isoniazid (INH) and pyrazinamide (PZA). A total of 25 single-nucleotide polymorphisms, including pregnane-X-receptor, were selected for analysis.RESULTS: TB drug concentrations were available in a subset of 101 patients: 58 in the MFX arm and 43 in the control arm. Baseline characteristics were well-balanced between study arms: median age and weight were respectively 36 years and 57.7 kg; 75.2% of the patients were living with HIV. Although weight-based drug dosing was the same in the two arms, we found that RIF exposure was increased by 19.3%, INH decreased by 19% and PZA decreased by 19.2% when administered as part of the MFX-containing regimen. Genetic variation in pregnane-X-receptor (rs2472677) was associated with a 25.3% reduction in RIF exposure.CONCLUSION: Optimised weight-based TB treatment dosing is essential when RIF, INH and PZA are co-administered with fluoroquinolones. The reduction in RIF exposure associated with pharmacogenetic variation is worrying.

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 coadministered 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 coadministration and compare dolutegravir trough concentrations with the IC 90 and EC 90 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 IC 90 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.