PrEP vs PEP
PrEP (Pre-Exposure Prophylaxis)
Indications
High-Risk Groups:
MSM, heterosexuals, transgender/gender-diverse persons at elevated risk
IV drug users with sharing equipment
Individuals with high HIV-related anxiety or foresee risk
Risk Assessment
Past 3-month behaviour: Condomless anal/vaginal sex, recent STIs, chemsex, needle sharing
Future/foreseeable risk: Travel to high-prevalence areas, leaving monogamous relationship, new partnerships
Investigations Prior to Initiation
HIV Testing: Must exclude existing HIV infection (acute HIV)
STI Screen: Hepatitis A/B/C, chlamydia, gonorrhoea, syphilis
Renal Function: eGFR >60 mL/min for safe use
Hepatitis B Status: Immunise if non-immune (tenofovir also active against HBV)
Discuss adherence and potential side effects (headache, nausea)
Monitoring
Every 3 Months: HIV test, STI testing
Kidney Function: At 3 months, then every 6 months if stable
Onset: Takes ~7 days for full rectal mucosal protection, possibly longer (21 days) for vaginal mucosa (some guidelines differ)
Side Effects: Headache, nausea (usually mild, self-limiting)
Check drug interactions (e.g., high-dose NSAIDs, other antivirals)
PEP (Post-Exposure Prophylaxis)
Post-exposure prophylaxis, must be started within 72 hours of possible exposure (sexual or needle-stick).
Typically 28-day course of combination antiretrovirals (e.g., tenofovir/emtricitabine + a third agent).
(Note: The “2-1-1 method” refers to on-demand (event-based) PrEP for MSM, not PEP. It is sometimes mistaken for PEP but is actually a type of PrEP used before and after intermittent exposures.)
On-Demand (Event-Based) PrEP (2-1-1) for MSM
Start: 2 tablets of tenofovir/emtricitabine 2–24 hours before sexual intercourse
Then: 1 tablet 24 hours after first dose, and 1 tablet 48 hours after first dose
Suited for infrequent sexual exposures (MSM).
Must ensure no existing HIV infection and normal renal function prior.
Summary of Differences
| | |
| Prevent HIV in high-risk individuals beforeexposure | Prevent HIV infection after a potential exposure |
| Daily or Event-Based (2-1-1) usage prior to risk | Within 72 hours of exposure, ideally ASAP |
| Ongoing (daily) for continuous risk, or short course around events (2-1-1 method) | 28-day regimen of antiretrovirals |
| Tenofovir/emtricitabine ± others if indicated (e.g. descovy or truvada) | Typically 2–3 drug combination: e.g. Tenofovir/emtricitabine + raltegravir or dolutegravir |
| HIV, STI screen, renal function every 3 months; more frequent if issues | Baseline HIV/renal function, repeat HIV testing at 4–6 weeks & 3 months post-exposure; LFTs, etc. |
Notes
PrEP reduces HIV acquisition risk by >90% when taken correctly.
PEP is emergency prophylaxis; start within 72 hours or efficacy drastically reduces.
On-demand PrEP (“2-1-1”) is not the same as PEP; it’s still a pre-exposure measure for those with intermittent exposures (commonly MSM).
Encourage safe sex, regular STI screening, and counselling for risk reduction.
