After tenofovir alafenamide dosing in vivo , tenofovir-dp was unquantifiable in most tissues (91%) although cervical and vaginal epithelial cells efficiently formed tenofovir-dp from tenofovir alafenamide in vitro . These findings warrant further investigation of tenofovir alafenamide's pharmacology.
The goal of this work was to evaluate dosing strategies for tenofovir disoproxil fumarate (TDF), tenofovir alafenamide (TAF), and emtricitabine (FTC) for pre-exposure prophylaxis (PrEP) with injection drug use with a pharmacokinetic/pharmacodynamics analysis of concentration data generated from two single-dose clinical studies conducted in healthy women. Population pharmacokinetic models were developed using measured intracellular metabolite, endogenous nucleotide competitors, and extracellular parent drug concentrations. Intracellular metabolite concentrations were normalized to endogenous competitors and compared with an EC target for PrEP efficacy. Monte Carlo simulations were used to select effective dose strategies of single agents (TAF, TDF, and FTC) and combinations (TDF + FTC and TAF + FTC). Daily, intermittent, and event-driven dosing regimens at varying dosage amounts were explored. When combined, TDF + FTC and TAF + FTC both provided quick (0.5 hours) and durable (up to 84 and 108 hours, respectively) protection of ≥99% after a single dose. When dosed twice per week, protection remained at 100%. Single-agent regimens provided lower estimates of protection than either combination tested. Here, the application of pharmacokinetic modeling to in vitro target concentrations demonstrates the added utility of including FTC in a successful PrEP regimen. While no TAF-based PrEP data are currently available for comparison, this analysis suggests TAF + FTC could completely protect against percutaneous exposure with as little as two doses per week.
The use of enteral feeding tubes to administer antiretroviral medication administration is necessary in certain patients with human immunodeficiency virus (HIV) infection. However, adequacy of drug exposures after these administration routes are largely unknown, making dosing recommendations and the attainment of viral suppression challenging in this patient population. This report describes a patient with advanced HIV infection and a complicated medical history, including long-term intractable nausea/vomiting necessitating antiretroviral medication administration via a Roux-en-Y jejunostomy (J)-tube. Pharmacokinetic assessments were performed to compare differences in antiretroviral drug absorption and plasma exposure following oral and J-tube administration of dolutegravir, tenofovir disoproxil fumarate, and emtricitabine. Results were also compared to published pharmacokinetic data in HIV-infected individuals. Exposure to dolutegravir and tenofovir were similar between J-tube and oral administration routes, whereas emtricitabine exposure was 38% lower when administered via J-tube. However, in comparison to reference data in HIV-infected individuals taking these medications orally, exposure to dolutegravir and tenofovir was 75%–76% and 55%–61% lower, respectively, following both routes of administration. Emtricitabine exposure was similar to and 71% higher than reference data following J-tube and oral administration, respectively. This report highlights the importance of performing pharmacokinetic assessments in patients with the potential for impaired drug absorption to ensure antiretroviral treatment success.
Two large Phase III HIV prevention trials conducted in women, FEM-PrEP and VOICE, failed to show HIV prevention efficacy for TDF taken with or without FTC 3,4 , whereas women in a third clinical trial, Partners PrEP, had a high degree of protection 2 . These results were attributed to differing rates of adherence in the studies. However, the degree of adherence needed to effectively prevent HIV infection may be dependent on the route of acquisition as evidenced by recent data from the iPrEX clinical trial demonstrating that two doses of Truvada ® per week were sufficient to reduce rectal HIV acquisition in MSM 5 . This same level of adherence failed to protect women against vaginal HIV acquisition in 4 .Together, these clinical trial data indicate the importance of understanding the relationship between drug concentrations at sites of HIV acquisition (pharmacokinetics [PK]) and efficacy (pharmacodymamics [PD]) in
Enteral tubes are necessary for certain patients; however, medication absorption can be affected by this route of administration potentially resulting in decreased efficacy. All first-line treatments for Hepatitis C Virus (HCV) infection are only available as tablets and may have decreased absorption if administered via an enteral tube.This report describes the first case of a pegylated interferon and ribavirin treatmentexperienced patient who successfully achieved HCV cure after 12 weeks of elbasvir/ grazoprevir administered via percutaneous gastrostomy tube. We further review the available pharmacokinetic and clinical literature regarding administration via enteral feeding tubes for all first-line direct-acting antivirals (DAAs). The literature suggests that crushed administration can be considered for DAAs in patients with gastric access. However, caution should be exercised in patients with extragastric enteral tubes and in those with altered gastrointestinal tract anatomy.
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