Fast Five Quiz: HIV Pre-exposure Prophylaxis: Selecting Appropriate Candidates

Jason F. Okulicz, MD


January 20, 2021

According to British HIV Association (BHIVA)/British Association for Sexual Health and HIV (BASHH) guidelines, same-day PrEP initiation can be considered for at-risk individuals who have a negative result on a third-generation or higher blood-based point-of-care test on the same day or for those with a negative result on a combined HIV antigen/antibody test in the preceding 4 weeks. HIV viral load measurement should be considered for patients who have had a high-risk exposure in the preceding month. PrEP should be deferred for individuals who report condomless anal intercourse in the preceding month and who are symptomatic of possible HIV seroconversion.

When starting PrEP, a 90-day supply of medication is suggested. Additional maintenance doses (90 days) can be prescribed after obtaining a negative combined HIV antigen/antibody test result.

PrEP is currently available in two combinations approved by the US Food and Drug Administration: tenofovir disoproxil fumarate-emtricitabine (TDF/FTC) and tenofovir alafenamide-emtricitabine (TAF/FTC). However, TDF/FTC has not been studied in cisgender women, and TDF/FTC is the only combination indicated to prevent HIV acquisition via receptive vaginal intercourse in cisgender women and transgender men.

The time from initiation of daily oral TDF/FTC to maximal protection is unknown. There is no scientific consensus on what intracellular concentrations are protective or the protective contribution of each drug in specific body tissues. Maximum intracellular concentrations of tenofovir diphosphate (the activated form of the medication) are reached in blood after approximately 20 days, in rectal tissue at approximately 7 days, and in cervicovaginal tissues at approximately 20 days. No data are yet available about intracellular drug concentrations in penile tissues to inform considerations of protection for male insertive sex partners.

For additional information regarding HIV PrEP, refer to the BHIVA/BASHH guidelines.

Learn more about initiating HIV PrEP.


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