MKSAP 18 "Quiz Me!" Question: Answer and Critique


D: Tenofovir disoproxil fumarate and emtricitabine daily

Educational Objective

Prevent HIV infection in persons at risk with pre-exposure prophylaxis.


The most appropriate preventive measure for this patient is daily tenofovir disoproxil fumarate and emtricitabine (TDF-FTC). He has multiple risk factors for acquiring HIV infection, including having sex with multiple partners without consistent condom use. Data support the use of pre-exposure prophylaxis (PrEP) in specific populations with ongoing high risk for infection, such as sexual partners of infected persons, men who have sex with men, and injection drug users. PrEP is recommended for persons in such groups who can adhere to the daily regimen. Efficacy has varied depending on adherence to the regimen; rates of reduction in new infections ranged from 42% to 75% and up to 92% in patients whose adherence was documented by monitoring drug blood levels. This patient is in a group shown in clinical trials to benefit from PrEP for HIV. Daily combination tenofovir alafenamide and emtricitabine is approved for PrEP as well, except in women engaging in receptive vaginal intercourse. Risk of kidney dysfunction from TDF is low, but kidney function should be checked every 6 months during PrEP. Patients taking PrEP should be counseled to continue using barrier precautions and should undergo testing for HIV, other sexually transmitted infections (STIs), and pregnancy in women, every 3 months.

TDF-FTC given as a single dose before or after each sexual exposure has not been proven effective, and because of concerns for lower effectiveness and possible selection for resistance, these methods should not be used for prevention.

Patients should be counseled regarding the need for continued barrier precautions during sex because the effectiveness of PrEP is less than 100% and to reduce transmission of other STIs. However, counseling the patient about consistent condom use without PrEP places the patient at unnecessary risk for HIV infection. PrEP and barrier protection is now the standard of prevention for men who have sex with men at risk for HIV infection.

Key Point

The combination of tenofovir disoproxil fumarate (or tenofovir alafenamide, except in women engaging in receptive vaginal intercourse) plus emtricitabine taken once daily is more than 90% effective, if taken consistently, in preventing HIV acquisition.


US Preventive Services Task Force, Owens DK, Davidson KW, Krist AH, et al. Preexposure Prophylaxis for the Prevention of HIV Infection: US Preventive Services Task Force Recommendation Statement. JAMA. 2019 Jun 11;321(22):2203-2213. doi: 10.1001/jama.2019.6390

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