Simulating Intestinal Transporter and Enzyme Activity in a Physiologically Based Pharmacokinetic Model for Tenofovir Disoproxil Fumarate.

Tenofovir disoproxil fumarate (TDF), a prodrug of tenofovir, has oral bioavailability (25%) limited by intestinal transport (P-glycoprotein), and intestinal degradation (carboxylesterase). However, the influence of luminal pancreatic enzymes is not fully understood. Physiologically based pharmacokinetic (PBPK) modeling has utility for estimating drug exposure from in vitro data. This study aimed to develop a PBPK model that included luminal enzyme activity to inform dose reduction strategies. TDF and tenofovir stability in porcine pancrelipase concentrations was assessed (0, 0.48, 4.8, 48, and 480 U/ml of lipase; 1 mM TDF; 37°C; 0 to 30 min). Samples were analyzed using mass spectrometry. TDF stability and permeation data allowed calculation of absorption rates within a human PBPK model to predict plasma exposure following 6 days of once-daily dosing with 300 mg of TDF. Regional absorption of drug was simulated across gut segments. TDF was degraded by pancrelipase (half-lives of 0.07 and 0.62 h using 480 and 48 U/ml, respectively). Previously reported maximum concentration (Cmax; 335 ng/ml), time to Cmax (Tmax; 2.4 h), area under the concentration-time curve from 0 to 24 h (AUC0-24; 3,045 ng · h/ml), and concentration at 24 h (C24; 48.3 ng/ml) were all within a 0.5-fold difference from the simulated Cmax (238 ng/ml), Tmax (3 h), AUC0-24 (3,036 ng · h/ml), and C24 (42.7 ng/ml). Simulated TDF absorption was higher in duodenum and jejunum than in ileum (p<0.05). These data support that TDF absorption is limited by the action of intestinal lipases. Our results suggest that bioavailability may be improved by protection of drug from intestinal transporters and enzymes, for example, by coadministration of enzyme-inhibiting agents or nanoformulation strategies.

Securing accelerated access to long-acting injectable cabotegravir for HIV prevention in low- and middle-income countries.

INTRODUCTION: Reductions in HIV acquisition have slowed, and the global community is significantly off track from global goals. Oral pre-exposure prophylaxis (PrEP) alone cannot address the diverse needs of the millions of people at risk of HIV acquisition. Long-acting injectable cabotegravir (CAB-LA) received United States Food and Drug Administration approval for HIV prevention in December 2021. When studied, CAB-LA demonstrated high effectiveness, provides months of protection versus daily use, is preferred by some users and has the potential to achieve commodity cost reduction. These factors position CAB-LA to catalyse transformation in HIV prevention. Significant work must be undertaken to ensure at-scale uptake in low- and middle-income countries. Leveraging decades of product introduction experience, Clinton Health Access Initiative (CHAI) has developed an innovative roadmap to support equitable CAB-LA introduction, comprising tightly executed market-shaping, product development, regulatory, and programmatic and implementation action. DISCUSSION: Proven models exist (e.g. long-acting reversible contraceptives, paediatric tuberculosis treatment and antiretrovirals (ARVs), such as paediatric dolutegravir and tenofovir disoproxil fumarate, lamivudine, and dolutegravir) for partnership-driven, accelerated, impactful product introduction. Based on learnings from these models and needs in the prevention space, CHAI developed a roadmap to maximize the near-term impact of CAB-LA and accelerate the development of, access to and impact of quality-assured, low-cost generic CAB-LA. This roadmap is intended to inform introduction planning and investment decision-making across a range of stakeholders, including donors, governments, manufacturers and other partners working in the HIV prevention space. Elements include (1) ensuring coordination and alignment across partners, and avoiding redundancy experienced during oral PrEP introduction; (2) preparing national programmes and providing support to maximize impact, including the development of national policies, guidelines and introduction plans; system strengthening; quantification and procurement; and addressing evidence needs, among other areas; (3) supporting community engagement, ensuring that demand generation and delivery approaches are person-centred and community-led; (4) incentivizing generic product development through, for example, milestone-based commercialization incentives and product development cost-sharing; and (5) expediting regulatory reviews. CONCLUSIONS: Accelerating access to affordable, generic CAB-LA can transform progress towards HIV epidemic control. This vision of impact at scale in prevention is achievable, if informed by results-backed approaches to introduction.

Pediatric COVID-19 Therapeutics: Seizing the Right Research and Development Opportunities to Accelerate Access for Children.

Children, although at lower risk of poor outcomes from COVID-19 relative to adults, still stand to benefit from therapeutic interventions. Understanding of COVID-19 clinical presentation and prognosis in children is essential to optimize therapeutic trials design. This perspective illustrates how to collectively accelerate pediatric COVID-19 therapeutic research and development, based on the experience of the Global Accelerator for Paediatric Formulations.

Advancing the prevention and treatment of HIV in children: priorities for research and development.

Safe and effective paediatric formulations of the most promising antiretroviral drugs are crucial to advance the treatment and prevention of HIV in neonates, infants, children, and adolescents. The WHO Paediatric Drug Optimization for HIV (PADO-HIV) group brings together stakeholders and experts every 2-3 years to identify priority products and define research gaps in the development of new HIV drugs and formulations for children in low-income and middle-income countries. PADO-HIV 5 met from Sept 27 to Oct 15, 2021. The group evaluated HIV agents from known and novel drug classes, oral and parenteral long-acting formulations, and developments in broadly neutralising antibodies, and included focused sessions on neonates and new delivery technologies. A list of medium-term and long-term priorities was generated, and research questions were defined. This forward-looking analysis is intended to provide guidance to funders, drug developers, and researchers, and to accelerate access for children to the best HIV drugs and formulations.

Adaption of an ongoing clinical trial to quickly respond to gaps in changing international recommendations: the experience of D2EFT.

A rapidly changing landscape of antiretrovirals and their procurement at scale has permitted the evaluation of new optimised second-line antiretroviral therapy (ART) in low- and middle-income countries. D2EFT is an open-label randomised controlled non-inferiority phase IIIB/IV trial in people living with HIV-1 (PWH) whose first-line non-nucleoside reverse transcriptase inhibitor (NNRTI)-based ART is failing. At inception, it compared a standard of care of boosted darunavir with two nucleos(t)ide reverse transcriptase inhibitors (NRTIs) to the novel NRTI-sparing regimen of boosted darunavir with dolutegravir. Implemented in 2017, participating sites were across Africa, Asia and Latin America. Around the time of implementation, the World Health Organization updated its treatment guidelines and recommended scaling up tenofovir disoproxil fumarate-lamivudine-dolutegravir (TLD). This situation pushed D2EFT investigators to consider the impact of the roll-out of TLD on the D2EFT research question. The protocol team agreed it was important to study TLD in second-line when an NNRTI regimen was failing, and focused on options to expedite the work by studying the question within the existing trial and network. All key issues (statistical, programmatic and financial) were reviewed to assess the benefits and risks of adding a third arm to the ongoing study, as opposed to developing a new randomised clinical trial with the same control arm and within the same network. The development of a new trial was deemed to be longer than adding a third arm, and to create a challenging situation with two competing clinical trials at the same sites which would slow down recruitment and impair both trials. On the other hand, adding a third arm would be demanding in terms of operationalisation, increased sample size and statistical biases to control. The optimal strategy was deemed to be the addition of a third arm, arriving retrospectively at a simplified multi-arm multi-stage clinical trial design to achieve statistical validity. The D2EFT study maintains additional value in a quickly evolving second-line ART strategy allowed by the progress in global access to ART.

Shortening the decade-long gap between adult and paediatric drug formulations: a new framework based on the HIV experience in low- and middle-income countries.

INTRODUCTION: Despite the coordinated efforts by several stakeholders to speed up access to HIV treatment for children, development of optimal paediatric formulations still lags 8 to 10 years behind that of adults, due mainly to lack of market incentives and technical complexities in manufacturing. The small and fragmented paediatric market also hinders launch and uptake of new formulations. Moreover, the problems affecting HIV similarly affect other disease areas where development and introduction of optimal paediatric formulations is even slower. Therefore, accelerating processes for developing and commercializing optimal paediatric drug formulations for HIV and other disease areas is urgently needed. DISCUSSION: The Global Accelerator for Paediatric Formulations (GAP-f) is an innovative collaborative model that will accelerate availability of optimized treatment options for infectious diseases, such as HIV, tuberculosis and viral hepatitis, affecting children in low- and middle-income countries (LMICs). It builds on the HIV experience and existing efforts in paediatric drug development, formalizing collaboration between normative bodies, research networks, regulatory agencies, industry, supply and procurement organizations and funding bodies. Upstream, the GAP-f will coordinate technical support to companies to design and study optimal paediatric formulations, harmonize efforts with regulators and incentivize manufacturers to conduct formulation development. Downstream, the GAP-f will reinforce coordinated procurement and communication with suppliers. The GAP-f will be implemented in a three-stage process: (1) development of a strategic framework and promotion of key regulatory efficiencies; (2) testing of feasibility and results, building on the work of existing platforms such as the Paediatric HIV Treatment Initiative (PHTI) including innovative approaches to incentivize generic development and (3) launch as a fully functioning structure. CONCLUSIONS: GAP-f is a key partnership example enhancing North-South and international cooperation on and access to science and technology and capacity building, responding to Sustainable Development Goal (SDG) 17.6 (technology) and 17.9. (capacity-building). By promoting access to the most needed paediatric formulations for HIV and high-burden infectious diseases in low-and middle-income countries, GAP-f will support achievement of SDG 3.2 (infant mortality), 3.3 (end of AIDS and combat other communicable diseases) and 3.8 (access to essential medicines), and be an essential component of meeting the global Start Free, Stay Free, AIDS Free super-fast-track targets.

Catalysing the development and introduction of paediatric drug formulations for children living with HIV: a new global collaborative framework for action.

Progress in the development and introduction of paediatric formulations for key infectious diseases is poor in low-income and middle-income countries (LMICs). Although major steps have been made in the scale-up of antiretroviral medicines in LMICs, the development and deployment of formulations for infants and children is suboptimal. Of the children living with HIV globally (most in Africa), only 43% are receiving antiretroviral therapy (ART), many with suboptimal formulations. These shortfalls pose a series of challenges to meeting global treatment targets of 1·6 million children (aged 0-14 years) on ART by the end of 2018 (95% coverage) and to ensuring that 95% of those on ART are virologically suppressed. The Global Accelerator for Paediatric Formulations (GAP-f) has been developed to accelerate research, development, regulatory filing, introduction, and uptake of prioritised paediatric antiretrovirals in age-appropriate formulations by 2020, with innovative, strategic, and sustainable financing. The GAP-f will build on existing efforts to maximise coordination and alignment of policy makers, research networks, regulatory agencies, funding organisations, and manufacturers in paediatric HIV and other paediatric diseases, including tuberculosis, viral hepatitis, and other infectious diseases. Paediatric drug development and scale-up will require special efforts to bring greater visibility and new solutions to ensure that children in LMICs have access to effective and appropriate treatment options.

Antiretroviral dose optimization: the future of efavirenz 400 mg dosing.

PURPOSE OF REVIEW: Antiretroviral (ARV) therapy costs in low-income and middle-income countries are major concerns, and lower doses of first-line treatment components, when possible, would save millions of dollars, which could be used to treat more people living with HIV. RECENT FINDINGS: The Encore-1 study, followed by a detailed pharmacokinetic analysis of efavirenz 400 versus 600 mg once daily, produced enough information for the most recent ARV treatment WHO guidelines to include efavirenz 400 mg among agents used for first-line treatment. However, data on efavirenz 400 mg plasma concentrations during pregnancy and when coadministered with rifampicin-containing antituberculosis (TB) treatment are not yet available as formal pharmacokinetic studies under these circumstances are ongoing. SUMMARY: Although efavirenz at a daily dose of 400 mg once daily in combination with tenofovir disoproxil fumarate and emtricitabine has shown noninferiority to the approved 600 mg once-daily dose, large global uptake has been delayed by the lack of data on drug exposure during pregnancy and anti-TB treatment. Knowledge on efavirenz 400 mg exposure in these scenarios will arise in mid-late 2017.

Development of a Novel Formulation That Improves Preclinical Bioavailability of Tenofovir Disoproxil Fumarate.

Tenofovir disoproxil fumarate (TDF), the bisphosphonate ester prodrug of tenofovir (TFV), has poor bioavailability due to intestinal degradation and efflux transport. Reformulation using U.S. Food and Drug Administration-approved esterase and efflux inhibitors to increase oral bioavailability could provide lower dose alternatives and reduce costs for patients with HIV in resource-limited settings. Inhibition of mucosal and intracellular esterases was studied in human and rat intestinal extracts (S9), where TDF was protected by the carboxylesterase inhibitor bis-para-nitrophenylphosphate, the ester mix EM1, and the generally recognized-as-safe (GRAS) excipient propylparaben. Permeability studies using Madin-Darby canine kidney and Caco-2 cell monolayers demonstrated that TDF was a substrate for the permeability glycoprotein with permeability glycoprotein inhibitors reducing basolateral to apical transport of TDF. These studies also showed that transport was increased by esterase inhibitors. TDF, TFV, and tenofovir monophosphonate ester transport across Caco-2 monolayers with esterase and efflux inhibitors revealed a maximum 38.7-fold increase in apical to basolateral TDF transport with the potent non-GRAS combination of EM1 and GF120918. Transport was increased 22.8-fold by the GRAS excipients, propylparaben, and d-a-tocopheryl polyethylene glycol 1000 succinate (a vitamin E derivative). TFV pharmacokinetics in rats following oral administration of TDF and GRAS esterase and efflux inhibitors confirmed enhanced bioavailability. Area under the curve increased 1.5- to 2.1-fold with various combinations of parabens and d-a-tocopheryl polyethylene glycol 1000 succinate. This significant inhibition of TDF hydrolysis and efflux in vivo exhibits the potential to safely increase TDF bioavailability in humans.