A case of a man contracting HIV while taking daily doses of Truvada as pre-exposure prophylaxis (PrEP) has led scientists to conclude that while PrEP is highly effective, it is possible for someone to get HIV when exposed to a virus resistant to both drugs in Truvada.
These findings were presented at the 2016 Conference on Retroviruses and Opportunistic Infections (CROI) in Boston.
Truvada is actually a combination of two drugs: tenofovir and emtricitabine. Recent research suggests that resistance to emtricitabine is more common, though mutations in HIV resistant to tenofovir have started to emerge. This recent case study, however, is the first time a virus has been resistant to both tenofovir and emtricitabine.
Evidence suggests that the individual in question, a 43-year-old man who has sex with men, adhered well to PrEP over the long-term. Nevertheless, after 24 months on Truvada he tested positive for HIV. Initial tests indicated that he was acutely (very recently) infected....Pharmacy records indicated that the man in the case study had consistently filled his Truvada prescription on schedule....
Tests also indicated that his drug resistance had been transmitted from another person, rather than acquired post-transmission. And a genetic analysis of his virus conducted on a sample taken a week after he tested positive suggested that he contracted the virus from a single individual.
According to Richard Harrigan, PhD, one of the researchers on the case study, this is not “a situation which calls for panic."
"It is an example that demonstrates that PrEP can sometimes be ineffective in the face of drug resistant virus, in the same way that treatment itself can sometimes be ineffective in the face of drug resistant virus," he said. "This case demonstrates that while PrEP is beneficial, we can’t rely on it to be an infallible magic bullet.”
Clinical and real-world trials have proven PrEP's efficacy at or near 100%, though the medication still leaves users open to other sexually transmitted infections, which is why the CDC recommends using PrEP in addition to—not instead of—condoms.