Potential Weak Interaction
Emtricitabine/Tenofovir-DF (FTC/TDF, PrEP)
Quality of Evidence:
Coadministration has not been studied. As para-aminosalicylic acid, emtricitabine and tenofovir are predominantly renally eliminated, including by active tubular secretion, there is potential for competition for elimination via renal transport proteins, which may lead to increased concentrations of aminosalicylic acid, emtricitabine or tenofovir. However, a clinical study performed with tenofovir and the calcium salt of para-aminosalicylic acid showed an unexpected substantial reduction in tenofovir exposure. The mechanism is unclear but could relate to reduced absorption in presence of the calcium salt of para-aminosalicylic acid. Until further data are available on the mechanism on the interaction, caution is needed when coadministering tenofovir with the calcium salt of para-aminosalicylic acid.
The effects of para-aminosalicylic acid -calcium formulation (PAS-Ca; 5.28 g twice daily) on the pharmacokinetics of tenofovir disoproxil fumarate (300 mg single dose) were studied in 18 healthy male Korean subjects. Coadministration significantly reduced tenofovir systemic exposure, with tenofovir Cmax decreasing by 67% and AUC decreasing by 71%. The mechanism is unclear but could relate to reduced absorption in presence of the calcium salt of para-aminosalicylic acid.
Para-aminosalicylic acid significantly reduced tenofovir exposure in human subjects; mismatched findings from in vitro to in vivo translational research. Parvez MM, Kalkisim S, Nguyen PTT, et al. Br J Clin Pharmacol. 2021. Epub ahead of print.
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