Despite significant progress in paediatric HIV treatment, optimal antiretroviral formulations for infants, children and adolescents remain limited. The paediatric antiretroviral drug optimization group regularly reviews medium-and long-term priorities for antiretroviral drug development, to guide industry and other stakeholders on formulations most needed for low-and middle-income countries. Ongoing medium-term priorities include a scored dispersible dolutegravir tablet (10mg), a dolutegravir-containing fixed-dose combination, and fixed-dose combinations containing tenofovir alafenamide. Darunavir/ritonavir combination tablet remain a priority for second-line treatment. Future treatment options of potential interest for paediatrics include broadly neutralizing antibodies, long acting/extended release formulations, and novel technologies. Issues specific to neonatal prophylaxis and treatment, and to the investigation of novel antiretrovirals in adolescents and pregnant and lactating women are also discussed. Continued focus on identifying, prioritizing and ensuring access to optimal formulations suitable for infants, children and adolescents is key to ensuring that global HIV treatment targets can be met.
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.
IntroductionDespite 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.DiscussionThe 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.ConclusionsGAP‐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.
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 (C max ; 335 ng/ml), time to C max (T max ; 2.4 h), area under the concentration-time curve from 0 to 24 h (AUC 0 -24 ; 3,045 ng · h/ml), and concentration at 24 h (C 24 ; 48.3 ng/ml) were all within a 0.5-fold difference from the simulated C max (238 ng/ml), T max (3 h), AUC 0 -24 (3,036 ng · h/ml), and C 24 (42.7 ng/ml). Simulated TDF absorption was higher in duodenum and jejunum than in ileum (pϽ0.05). 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.KEYWORDS tenofovir disoproxil fumarate, physiologically based pharmacokinetic modeling, HIV, bioavailability, HAART H uman immunodeficiency virus (HIV) is the cause of a currently incurable disease which constitutes a serious global health crisis. Oral antiretroviral therapy is the mainstay of current therapy and involves coadministration of drugs targeting multiple viral targets. Both drug-related adverse reactions and drug resistance have led to the development of newer antiretroviral drugs and drug classes. However, the cost and dosing schedule of treatments are a significant concern in low-and middle-income countries (L&MICs). Several effective antiretroviral drugs are now manufactured as generics and are marketed with significant cost savings to payers (1, 2).Tenofovir disoproxil fumarate (TDF), a prodrug of tenofovir (TFV), is a cornerstone of first-line treatment in low-income and middle-income countries. TDF is a nucleotide
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.
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