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In addition to the safety data obtained in PrEP clinical trials, data on drug-drug interactions and longer-term toxicities have been obtained by studying the component drugs individually for their use in treatment of people with HIV infection. Studies have also been performed in small numbers of healthy adults without HIV infection. No significant effect was seen, and no dosage adjustment was necessary for TD*, but there are no data on FTC (21, 22).

FTC and TD* are primarily excreted by the kidneys by a combination of glomerular filtration and active tubular secretion. Since both drugs are primarily eliminated by the kidneys, co-administration of TD*/ FTC with drugs that reduce renal function or compete for active tubular secretion may increase serum concentrations of TD*, FTC and other renally eliminated drugs including (but not limited to) cidofovir, aciclovir, valaciclovir, ganciclovir, valganciclovir, aminoglycosides and high-dose or multiple nonsteroidal anti-inflammatory drugs (21).

Cocaine, methamphetamine and alcohol use were not seen to influence the concentrations of PrEP drugs (23) but use of these drugs may have an effect on the person’s ability to maintain full adherence to PrEP.