Tim R Cressey’s research while affiliated with Chiang Mai University and other places

Background Tenofovir diphosphate concentration in red blood cells is an objective measure of long-term oral pre-exposure prophylaxis (PrEP) or antiretroviral therapy (ART) adherence. However, current methods for measuring tenofovir diphosphate are equipment and capital intensive, limiting widespread adoption. Objectives Low cost, rapid diagnostics for measuring tenofovir diphosphate may drive clinical adoption of routine drug level measurement as a tool for adherence monitoring of tenofovir disoproxil fumarate-based PrEP or ART. We validate a simple and accessible enzymatic assay [REverSe TRanscrIptase Chain Termination (RESTRICT)] for measuring tenofovir diphosphate in dried blood spots (DBS) obtained from a directly observed therapy study of individuals on PrEP. Methods We performed RESTRICT measurements on 74 DBS samples from individuals on tenofovir disoproxil fumarate/emtricitabine regimens. We compared RESTRICT measurements with those from a gold-standard method of liquid chromatography tandem mass spectrometry (LC-MS/MS). The ability of RESTRICT to correctly classify DBS tenofovir diphosphate concentrations to established steady-state adherence benchmark concentrations was determined using area under receiver operating characteristic curves (AUCs). Results The RESTRICT measurements of DBS samples were highly correlated with LC-MS/MS measurements of tenofovir diphosphate from DBS (r = −0.90; P < 0.0001). The RESTRICT assay correctly classified DBS samples as above or below established steady-state adherence benchmark concentrations corresponding to low (AUC = 0.974), moderate (AUC = 0.936) and high (AUC = 0.955) levels of adherence. Conclusions The enzymatic RESTRICT assay can accurately measure tenofovir diphosphate concentrations in DBS specimens using simple procedures and readily available laboratory equipment, offering accessible objective adherence monitoring for persons receiving tenofovir disoproxil fumarate-based PrEP or ART.

We investigated the steady-state pharmacokinetics of generic abacavir (ABC)/lamivudine (3TC) dispersible tablets (DTs) in young children living with HIV aged 3 months to <7 years, weighing 6 to <20 kg. Twenty-eight Thai children were enrolled and received ABC/3TC-DT plus pediatric dolutegravir-DT once daily. ABC/3TC was administered using WHO weight band (WB) doses: 180/90 mg, 240/120 mg and 300/150 mg for children weighing 6 to <10 kg (WB 1, n = 7), 10 to <14 kg (WB2, n = 9) and 14 to <20 kg (WB3, n = 12), respectively. ABC geometric mean (GM) AUC 0–24 h (CV%) was 14.2 (50.5%), 15.6 (32.6%) and 20.7 (28.3%) mg.h/L, respectively, and 3TC GM AUC 0–24 h was 14.8 (44.1%), 18.2 (28.0%) and 19.9 (26.2%) mg.h/L, respectively. ABC and 3TC exposures were within target ranges across WBs. These data supported current ABC/3TC-DT WHO-weight band dosing guidance for young children in Thailand.

This sub‐study sought to characterize the pharmacokinetics (PK) of favipiravir (FPV) within Thai adults and quantitatively assess differences in exposure to those previously reported in other populations as a basis to understand putative differences in efficacy between studies conducted in different regions. It was nested within a prospective trial of adults with symptomatic COVID‐19 infection without pneumonia receiving 1800 mg FPV twice‐daily on day 1 and 800 mg twice‐daily thereafter. Individual PK profiles were fitted with a one‐compartment disposition model (first‐order absorption). Eight adults (seven female) with a median age of 39 years and BMI of 27.9 kg/m² were included. Seven adults achieved plasma concentrations above the EC90 in vitro target (25 mg/L), with minimum–maximum concentrations decreasing with repeat dosing. The mean FPV apparent clearance observed in this study was 1.1 L/h (coefficient of variation [CV]: 60%), apparent volume of distribution 20.6 L (CV: 40%), absorption rate constant 6.1 h (CV: 100%), and 2.4 daily % change in apparent clearance (CV: 315%). Higher exposures were observed in these Thai adults compared with data from previous studies in Chinese, Japanese, and Turkish populations, respectively. Current FPV doses recommended in Thailand achieved target plasma concentrations with higher exposures than those described previously in other populations. The limited sample size prohibits firm conclusions from being drawn but the presented data warrants confirmation with a view to interrogate the appropriateness of doses used in randomized clinical trials that failed to demonstrate efficacy.

Treatment options for children living with HIV have historically been less effective, less practical and more difficult to implement compared with those for adults, as the research and development of new drugs for children has lagged behind. Significant progress has been achieved in response to the paediatric HIV epidemic over the last decade. Several optimised paediatric antiretroviral formulations are currently available or in development, including fixed-dose combination tablets containing a complete World Health Organization-recommended regimen. Despite these advancements, virological suppression rates in children are generally lower than in adults. Even when oral fixed-dose combinations with the optimal target profiles are developed, for some children virological suppression is not achievable for reasons such as adherence challenges, intolerance, toxicity and genotypic resistance. New safe, effective, well-tolerated antiretroviral agents from existing and novel classes, as well as innovative administration strategies are essential. To achieve the UNAIDS target of virological suppression in 95% of children receiving antiretroviral therapy, concerted efforts are required. This includes identifying priority drugs in line with latest developments, focusing drug development studies on these priorities, ensuring a timely technical knowledge transfer between originator and generic companies, accelerating regulatory approvals and facilitating procurement and implementation in countries. Success in these efforts depends on collaboration among all stakeholders, including communities, researchers, pharmaceutical companies, guideline and policymakers, governments, funders, regulators and healthcare providers. This review outlines which paediatric antiretroviral therapies are currently available, those which are under development and the future directions of paediatric HIV treatment.

Background/Objectives: Rivaroxaban and dabigatran are commonly used for thromboembolic disease management in active cancer patients. However, limited research explores the impact of concurrent chemotherapy on the pharmacodynamics of direct oral anticoagulants (DOAC). The aim of our study was to evaluate the impact of combined chemotherapy with rivaroxaban and dabigatran on the pharmacodynamics in patients with diffuse large B-cell lymphoma (DLBCL).; Methods: This was a prospective, pharmacodynamic study. Eligible subjects were ≥18 years old, diagnosed with DLBCL and initiating R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone) immunochemotherapy. The enrolled adults received either rivaroxaban (10 mg once daily) or dabigatran etixalate (110 mg twice daily). Plasma anti-factor Xa (FXa) in participants on rivaroxaban and diluted thrombin time (dTT) in participants on dabigatran were assessed over the dosing interval before and after R-CHOP administration. Pharmacodynamic parameters of rivaroxaban and dabigatran were determined using a non-compartmental analysis.; Results: Twenty-six adults participated, with twelve in the rivaroxaban group and fourteen in the dabigatran group. The mean age was 59 ± 14.4 years. In the rivaroxaban group, the AUEC of FXa inhibition showed no significant change after R-CHOP (mean difference 3.8 ng·h/mL, 95% confidence interval (CI) −155.4 to 163.0, p = 0.96). Similarly, in the dabigatran group, the AUEC of dTT remained unchanged post R-CHOP (mean difference 54.41 ng·h/mL, 95% CI −99.09 to 207.9 ng/mL, p = 0.46). However, the median time-to-peak dTT was significantly faster with R-CHOP (3 h, [min–max, 1.5–8] compared to without it (4 h, [min–max, 3–8], p = 0.04); Conclusions: Concurrent R-CHOP chemotherapy did not significantly impact FXa inhibition by rivaroxaban or dTT by dabigatran. The time-to-peak dTT was faster when dabigatran was administered with R-CHOP.

Objectives To develop a pragmatic twice daily lamivudine dosing strategy for preterm infants from 24 to 37 completed weeks of gestation. Methods Data were combined from eight pharmacokinetic studies in neonates and infants receiving lamivudine oral solution. A population pharmacokinetic model was developed using non-linear mixed effects regression. Different lamivudine dosing strategies, stratified by gestational age at birth (GA) bands, were simulated in a virtual population of preterm infants, aimed at maintaining lamivudine drug exposures (AUC0-12) within a reference target range of 2.95 to 13.25 µg·h/mL, prior to switching to WHO-weight band doses when ≥4 weeks of age and weighing ≥3 kg. Results A total of 154 infants (59% female) contributed 858 lamivudine plasma concentrations. Median (range) GA at birth was 38 (27–41) weeks. At the time of first pharmacokinetic sampling infants were older with median postnatal age (PNA) of 6.3 (0.52–26.6) weeks. Lamivudine concentrations were described by a one-compartment model, with CL/F and V/F allometrically scaled to weight. Maturation of CL/F was described using an Emax model based on PNA. CL/F was also adjusted on GA to allow extrapolation for extreme prematurity. Simulations predicted an optimal lamivudine dosing for infants GA ≥24 to <30 weeks of 2 mg/kg twice daily from birth until weighing 3 kg; and for GA ≥30 to <37 weeks, 2 mg/kg twice daily for the first 4 weeks of life, followed by 4 mg/kg twice daily until weighing 3 kg. Conclusions Model-based predictions support twice daily pragmatic GA band dosing of lamivudine for preterm infants, but clinical validation is warranted.

Once-daily fixed-dose combinations (FDC) containing abacavir (ABC), dolutegravir (DTG), and lamivudine (3TC) have been approved in the US for adults and children with HIV weighing ≥ 6 kg. This analysis assessed the ability of previously developed ABC, DTG, and 3TC pediatric population pharmacokinetic (PopPK) models using multiple formulations to describe and predict PK data in young children using dispersible tablet (DT) and tablet formulations of ABC/DTG/3TC FDC in the IMPAACT 2019 study. IMPAACT 2019 was a Phase I/II study assessing the PK, safety, tolerability, and efficacy of ABC/DTG/3TC FDC in children with HIV-1. Intensive and sparse PK samples were collected over 48 weeks. Existing drug-specific pediatric PopPK models for ABC (2-compartment), DTG (1-compartment), and 3TC (1-compartment) were applied to the IMPAACT 2019 drug concentration data without re-estimation (external validation) of PopPK parameters. Drug exposures were then simulated across World Health Organization weight bands for children weighing ≥ 6 to < 40 kg for each drug and compared with pre-defined exposure target ranges. Goodness-of-fit and visual predictive check plots demonstrated that the previously developed pediatric PopPK models sufficiently described and predicted the data. Thus, new PopPK models describing the IMPAACT 2019 data were unnecessary. Across weight bands, the predicted geometric mean (GM) for ABC AUC0–24 ranged from 14.89 to 18.50 μg*h/ml, DTG C24 ranged from 0.74 to 0.95 μg/ml, and 3TC AUC0–24 ranged from 10.50 to 13.20 μg*h/ml. These exposures were well within the pre-defined target ranges set for each drug. This model-based approach leveraged existing pediatric data and models to confirm dosing of ABC/DTG/3TC FDC formulations in children with HIV-1. This analysis supports ABC/DTG/3TC FDC dosing in children weighing ≥ 6 kg.