Q and A


Will HIV test window period before PrEP lead to drug resistance?

TDF/TFC (Truvada) both prevents and helps to treat HIV. I’ve heard that it is very important to get tested before you start taking PrEP because if you have the virus and start taking truvada you can build drug resistance. Also important to notice that heathcare providers worldwide are planning to use PrEP in their prevention strategy.

But some people will receive a negative test whie actually being in the first weeks of HIV infection for example. It is uncertain when these individuals will next test for HIV test, so they would be positive and also taking truvada which is not a fully ART treatment – because it lacks a third drug like an integrase inhibitor.

My question is: will this situation (a certain amount of people unaware of their positive status using truvada as PrEP) result in a rapid surge of a drug-resistant HIV? Will these meds stop working as PrEP if this TDF/FTC-resistant strain spreads?



Thanks for you questions – all good ones.

PrEP guidelines recommend taking very recent potential HIV risk into account before starting PrEP. This caution should include that the HIV test results only refers to your HIV status 3-4 weeks before the test.

If someone has been at risk of HIV in the few weeks before the test, they should be offered an additional HIV tests a month later.

Although cases of drug resistance to PrEP drugs under these circumstances have been, luckily these are not very common. This doesn’t make the first HIV test after starting PrEP a particularly important one.

Large PrEP studies didn’t show a risk of major drug resistance as very few cases of drug resistance have been reported. A caution about the one-month testing window though is a good one.


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