February 01, 2017
2 min read

Letter describes PrEP failure in Canadian patient who contracted HIV

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A letter published in The New England Journal of Medicine described what is considered to be the first case of a patient contracting HIV despite long-term adherence to pre-exposure prophylaxis, or PrEP.

David C. Knox, MD, of the Maple Leaf Medical Clinic in Toronto, first presented data about the case in February 2016. Knox said it was the first case to demonstrate failure with Truvada (emtricitabine/tenofovir disoproxil fumarate, Gilead Sciences; FTC/TDF), which is associated with nearly 100% (95% CI, 86-100) HIV prevention efficacy in patients who adhere to treatment.

The patient, a man aged 43 years from Toronto who reported having sex with men, initiated FTC/TDF in April 2013 and had seven nonreactive fourth-generation HIV screening tests over the next 21 months before testing positive for HIV, according to Knox and colleagues. They said tests supported clinical suspicion that the patient was infected during reported condomless anal receptive sex with multiple partners 2 to 6 weeks before testing positive.

According to Knox and colleagues, the patient reported “perfect” adherence to FTC/TDF over 24 months. Knox said there was no reason to doubt the claim, which was backed up by testing and pharmacy records.

“He was adherent to Truvada,” Knox told Infectious Disease News.

Knox and colleagues said the failure of FTC/TDF in the patient was “probably” due to a mutation, M184V, which compromises FTC activity; plus several thymidine analogue mutations, revertant substitutions (or both), which slightly decrease TDF susceptibility.

Knox said the letter includes new information not presented at CROI last year, including patient data from Vancouver on the prevalence of circulating HIV virus with specific FTC/TDF-resistant mutations. Such data were not available for Toronto, Knox and colleagues said.

According to them, 1.7% of the Vancouver patients had a plasma sample that contained virus that was resistant to FTC, compared with 0.004% that were resistant to TDF and 0.001% resistant to both.

“Continued surveillance of mutations that may affect the efficacy of pre-exposure prophylaxis is needed,” Knox and colleagues wrote. They said patients should be counseled on the use of FTC/TDF as part of a “combination approach to HIV prevention.”

“PrEP, like anything in medicine, in not 100% effective,” Knox told Infectious Disease News. “Patients can use this information and decide what is right for them when considering their sexual practices. PrEP plus condoms is your best defense against HIV.” – by Gerard Gallagher


Knox DC, et al. N Engl J Med. 2017;doi:10.1056/NEJMc1611639.

Disclosure: Please see the full letter for a list of all authors’ relevant financial disclosures.