Fundamental aspects of long-acting tenofovir alafenamide delivery from subdermal implants for HIV prophylaxis.

Global efforts aimed at preventing human immunodeficiency virus type one (HIV-1) infection in vulnerable populations appear to be stalling, limiting our ability to control the epidemic. Long-acting, controlled drug administration from subdermal implants holds significant potential by reducing the compliance burden associated with frequent dosing. We, and others, are exploring the development of complementary subdermal implant technologies delivering the potent prodrug, tenofovir alafenamide (TAF). The current report addresses knowledge gaps in the preclinical pharmacology of long-acting, subdermal TAF delivery using several mouse models. Systemic drug disposition during TAF implant dosing was explained by a multi-compartment pharmacokinetic (PK) model. Imaging mass spectrometry was employed to characterize the spatial distribution of TAF and its principal five metabolites in local tissues surrounding the implant. Humanized mouse studies determined the effective TAF dose for preventing vaginal and rectal HIV-1 acquisition. Our results represent an important step in the development of a safe and effective TAF implant for HIV-1 prevention.

Prescribing rates and characteristics of recipients of tenofovir-containing regimens before and after market entry of tenofovir alafenamide.

BACKGROUND: Tenofovir alafenamide (TAF) is a new formulation of tenofovir disoproxil fumarate (TDF) that was approved in 2015. While clinical trial evidence suggests that TAF has more favorable outcomes related to kidney injury and loss of bone mineral density, TAF also leads to higher lipid levels compared with TDF. OBJECTIVES: To (a) determine prescribing rates of TDF and TAF among new recipients from 2014 to 2018 in a large academic health system and (b) compare baseline patient characteristics of those newly prescribed TDF versus TAF before and after the approval of TAF in November 2015. METHODS: Electronic health record data were used to identify new recipients of TDF or TAF from 2014 to 2018 and describe their total monthly TDF and TAF prescriptions by indication. Patient characteristics were compared among new recipients of TDF before November 2015, new recipients of TDF after November 2015, and new recipients of TAF. RESULTS: Monthly TAF prescribing rates increased to match TDF prescribing rates by April 2018 (82 vs. 88 prescriptions per month). TAF recipients and new recipients of TDF before November 2015 had similar racial distributions; both of these groups were more likely to be Black compared with new recipients of TDF after November 2015 (55% and 53% vs. 37%; P < 0.0001). TAF recipients also tended to have more comorbidities, including chronic kidney disease (7% vs. 2% and 2%; P < 0.0001), hepatitis C virus (8% vs. 5% and 3%; P < 0.0001), diabetes (13% vs. 5% and 6%; P < 0.0001), hypertension (27% vs. 13% and 13%; P < 0.0001), coronary artery disease (5% vs. 3% and 2%; P < 0.0001), hyperlipidemia (21% vs. 6% and 7%; P < 0.0001), and congestive heart failure (3% vs. 1% and 1%; P < 0.0001), compared with both new recipients of TDF before and after November 2015. CONCLUSIONS: TAF prescribing rates grew substantially in the 2.5 years after FDA approval. TAF is being prescribed more often than TDF in patients with chronic kidney disease and in patients with cardiovascular disease, suggesting that prescribers may be prioritizing the kidney safety profile over the effect on lipids. DISCLOSURES: This work was supported by the Duke Clinical Research Institute Executive Director's Pathway for Supplemental Funding. The research team received additional support from the National Institute of Diabetes, Digestive, and Kidney Disease R01DK112258 and P01DK056492 (CW) and from the National Institute of Allergy and Infectious Diseases 5T32AI100851 (MHM). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Hung reports past employment by Blue Cross Blue Shield Association and CVS Health and a grant from Pharmaceutical Research and Manufacturers of America (PhRMA), unrelated to this work. The other authors have nothing to disclose. This work was accepted as a poster presentation for the AMCP Nexus 2020 Virtual, October 19-23, 2020.

Mechanism for effective lymphoid cell and tissue loading following oral administration of nucleotide prodrug GS-7340.

GS-7340 is a prodrug of tenofovir (TFV) that more efficiently delivers TFV into lymphoid cells and tissues than the clinically used prodrug TFV disoproxil fumarate, resulting in higher antiviral potency at greatly reduced doses and lower systemic TFV exposure. First-pass extraction by the intestine and liver represents substantial barriers to the oral delivery of prodrugs designed for rapid intracellular hydrolysis. In order to understand how GS-7340 reduces first-pass clearance to be an effective oral prodrug, its permeability and stability were characterized in vitro and detailed pharmacokinetic studies were completed in dogs. GS-7340 showed concentration-dependent permeability through monolayers of caco-2 cells and dose-dependent oral bioavailability in dogs, increasing from 1.7% at 2 mg/kg to 24.7% at 20 mg/kg, suggesting saturable intestinal efflux transport. Taking into account a 65% hepatic extraction measured in portal vein cannulated dogs, high dose GS-7340 is nearly completely absorbed. Consistent with the proposed role of intestinal efflux transport, coadministration of low dose GS-7340 with a transport inhibitor substantially increased GS-7340 exposure. The result of effective oral absorption and efficient lymphoid cell loading was reflected in the high and persistent levels of the pharmacologically active metabolite, TFV diphosphate, in peripheral blood mononuclear cells following oral administration to dogs. In conclusion, GS-7340 reaches the systemic circulation to effectively load target cells by saturating intestinal efflux transporters, facilitated by its high solubility, and by maintaining sufficient stability in intestinal and hepatic tissue.