Journal of pharmaceutical sciences 2016 12 14106(3) 906-919 pii 10.1016/j.xphs.2016.12.003
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.