A gay man who apparently adhered to the daily regimen of Truvada (tenofovir/emtricitabine) as pre-exposure prophylaxis (PrEP) has contracted a multi-drug resistant HIV virus strain.
Researches says that this case is rare and inconclusive but it might be possible for individuals who are adhere to PrEP to contract HIV when they are exposed to a virus that is resistant to both drugs included in Truvada.
David Knox, MD, an HIV specialist at Tronto’s Maple Leaf Medical Clinic and the lead author of the case study, presented findings at the 2016 Conference on Retroviruses and Opportunistic Infections (CROI) in Boston.
He reported the patient is a 43-year-old gay man who had been on PrEP for two years and has an HIV-positive partner who was undetectable on antiretroviral therapy, as well as having casual sex contacts.
According to pharmacy records the man in the case study had consistently filled his Truvada prescription on schedule. Dried blood-spot testing on a sample taken 16 days after he tested positive for HIV indicated that he had adhered well to Truvada during the previous one to two months, a period that overlapped with the estimated time when he contracted the virus.
Tests for antiretroviral (ARV) resistance that were conducted on a sample taken a week after the man tested positive for HIV drug resistant strain that had been transmitted from another person, rather than acquired post-transmission. 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.
Despite all these resistance mutations, the man in the case study is currently on successful HIV treatment, with a fully suppressed undetectable viral load.
“After 32 years of experience with HIV research, I have learned never to say ‘never’,” said Robert M. Grant, MD, MPH, a professor at the University of California, San Francisco, who was the head of the iPrEx trial that first proved PrEP’s effectiveness among MSM and transgender women in 2010. “Yet I also think that gay men benefit from feeling safer during sex, and I am grateful that PrEP affords that feeling.”
Although this single case raises some concern experts in the PrEP field believe that such failures of PrEP will remain rare.
According to research people who take PrEP at least four times a week are more than 99 percent protected against HIV.
Recent research suggested that, among HIV-positive individuals failing treatment regimens, resistance to tenofovir, which is the most commonly prescribed ARV in the world, is increasing. Perhaps as much as 1 percent of all individuals who contract HIV today inherit virus that has mutations conferring resistance to tenofovir. Resistance to emtricitabine is more common, likely because only a single resistance mutation is required to confer resistance to that drug, while for tenofovir more than one mutation is usually required.
According to Grant an HIV virus that is highly resistant to both tenofovir and emtricitabine, as in this new case report, is extremely rare, and was found only in this person alone out of more more than 9,200 participants in the clinical trials of PrEP.
Reflecting on the new case study, Dr. Richard Harrigan, one of the researchers on this case study said: “I certainly don’t think that this is 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 added, “This case demonstrates that while PrEP is beneficial, we can’t rely on it to be an infallible magic bullet.”
Commenting on the case, Gus Cairns, an expert on PrEP and AIDSmap Editor, said: “It is not unexpected that there would be occasional cases of PrEP failure; but the fact that this is the first case report among the tens of thousands of people now taking PrEP shows that it is very rare.”