HIV Pre-Exposure Prophylaxis
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Direct answer
HIV pre-exposure prophylaxis, or PrEP, is the use of antiretroviral drugs by HIV-negative people to prevent acquisition of HIV before exposure. The standard oral regimen is tenofovir disoproxil fumarate with emtricitabine, taken once daily, and it protects only when adherence is sustained. Confirming HIV-negative status, checking renal function and screening for hepatitis B are essential before the first dose.
What you must remember
- Eligibility: HIV-negative adults at substantial ongoing risk, including serodiscordant partners, men who have sex with men, transgender women, sex workers, people who inject drugs and those with recent sexually transmitted infections.
- Oral regimen: tenofovir disoproxil fumarate 300 mg with emtricitabine 200 mg once daily; tenofovir alafenamide with emtricitabine is an alternative with less renal and bone toxicity.
- Pre-test checks: a fourth-generation HIV antigen-antibody test to exclude infection, serum creatinine with estimated clearance, and hepatitis B surface antigen.
- Hepatitis B link: both drugs are active against hepatitis B virus, so stopping the regimen in a coinfected person can cause a severe hepatitis flare.
- Monitoring: HIV testing about every three months, periodic creatinine checks, more often with kidney risk, plus STI screening and an adherence review at each visit.
- Long-term toxicity: renal tubular injury and loss of bone mineral density are concerns with prolonged tenofovir disoproxil use.
- Post-exposure prophylaxis: a separate 28-day course started within 72 hours of a single exposure, never a substitute for PrEP in ongoing risk.
- Newer options: long-acting injectables such as cabotegravir are approved in some countries, and availability depends on the national programme.
A pathway from risk assessment to sustained use
PrEP is a schedule of tests, prescriptions and follow-up rather than a single prescription. Each step protects the person and protects the regimen from failure.
- Assess the risk: take a sexual and drug-use history, ask about partner status and recent exposures, and discuss how the person would use PrEP.
- Exclude HIV first: confirm negative status with a fourth-generation antigen-antibody test. Starting tenofovir-emtricitabine in undiagnosed infection risks selecting drug resistance.
- Check the kidneys and liver: measure serum creatinine and estimated clearance, and test for hepatitis B surface antigen. Reduced clearance calls for a review of the regimen before starting.
- Prescribe and counsel: start one tablet daily and explain that protection takes days to build up, longer after vaginal exposure. Missed doses reduce protection, so adherence is the central teaching point.
- Follow up regularly: repeat HIV testing about every three months, recheck renal function periodically, and address side effects such as early nausea or headache.
- Plan the stop: when PrEP is stopped, continue HIV testing for a period afterwards, because infection acquired during the tail of exposure can be missed.
Where the exam tries to catch you
Questions on PrEP usually turn on the testing sequence, the hepatitis B trap and the difference from PEP.
- Trap: starting PrEP in someone who looks well without testing Correct: HIV must be excluded first, because prescribing into undiagnosed infection can select resistance.
- Trap: stopping tenofovir-emtricitabine in a patient with hepatitis B without a plan Correct: discontinuation can trigger a severe flare, so liver monitoring must continue.
- Trap: confusing PrEP with PEP Correct: PEP is a 28-day course begun within 72 hours of exposure, whereas PrEP is taken continuously before exposure.
- Trap: dropping condoms once on PrEP Correct: PrEP prevents HIV only, so other sexually transmitted infections still need separate protection.
Frequently asked questions
Which tests must be done before starting HIV pre-exposure prophylaxis?
Confirm HIV-negative status with a fourth-generation antigen-antibody test, check serum creatinine with estimated clearance, and screen for hepatitis B surface antigen. Baseline screening for other sexually transmitted infections is also part of the assessment before PrEP begins.
Why does hepatitis B status matter in HIV pre-exposure prophylaxis?
Tenofovir and emtricitabine are both active against hepatitis B virus, so the regimen can suppress the virus in a coinfected person. Stopping PrEP in someone with hepatitis B can cause a severe hepatitis flare, so liver function must be monitored after discontinuation.
How does PrEP differ from post-exposure prophylaxis for HIV?
PrEP is a daily regimen taken before exposure to keep an HIV-negative person protected. Post-exposure prophylaxis is a 28-day course started within 72 hours after a single high-risk exposure. The two are not interchangeable, and PEP does not replace PrEP for someone at ongoing risk.
Which oral regimen is standard for HIV pre-exposure prophylaxis?
Tenofovir disoproxil fumarate 300 mg with emtricitabine 200 mg, taken once daily, is the standard oral regimen. Tenofovir alafenamide with emtricitabine is an alternative with less renal and bone toxicity, and the choice depends on local guidance.
What monitoring does a person on HIV pre-exposure prophylaxis need?
HIV testing about every three months, periodic creatinine checks, STI screening and an adherence review form the core monitoring. People with kidney risk need more frequent renal function tests while taking the regimen.