HIV and Post-Exposure Prophylaxis (PEP)

🧬 HIV Post-Exposure Prophylaxis (PEP) - UK Guideline-Based Practical Guide

⏱️ What is PEP?
PEP (Post-Exposure Prophylaxis) is a time-critical 28-day course of combination antiretroviral therapy given after a significant potential exposure to HIV, to reduce the chance of HIV establishing infection. PEP works best when started as soon as possible (ideally within 24 hours) and is generally not recommended if starting beyond 72 hours after exposure.

1️⃣ ✅ When should PEP be considered?

• PEP is considered for exposures with a meaningful transmission risk, including:
  • 🍑 Sexual exposure: condomless receptive anal intercourse (highest sexual risk), condom failure with anal sex, or other high-risk exposures depending on source viral status and exposure details.
  • 🩸 Occupational exposure: percutaneous injury (e.g., hollow-bore needle), mucous membrane splash with blood/body fluid, or rarely a bite in clearly blood-to-blood scenarios.
  • 💉 Injecting exposure: sharing needles or injecting equipment in higher-risk contexts, including sexualised drug use (“chemsex”).
  • 🚨 Sexual assault: assess urgently; consider PEP where exposure risk is significant (often via SARC/ED pathways).
• PEP is usually NOT indicated for negligible-risk exposures, for example:
  • 🧷 Community needlestick injuries (generally not recommended).
  • 👄 Oral sex exposures (usually negligible unless blood present and high-risk circumstances).
  • 🦷 Human bites (generally not recommended; consider only in rare, clear blood-to-blood high-risk scenarios).
• Key risk-assessment principle 🔎 depends on:
  • 📌 Type of exposure (anal vs vaginal vs oral; percutaneous vs splash).
  • 🧑‍⚕️ Whether the source is known HIV-positive and whether they have a documented undetectable viral load (U=U context).
  • 🌍 If source status unknown: local prevalence + likelihood of transmissible viraemia.

2️⃣ ⏰ Timing - the “72-hour rule”

• ⚡ Start immediately (ideally within 24 hours).
• 🕒 Can be considered up to 72 hours after exposure.
• ⛔ Do not start beyond 72 hours unless specialist advice for exceptional circumstances.
• 📅 Duration: 28 days (full course; avoid starter packs where possible).

3️⃣ 🏥 Where can patients access PEP in the UK?

• 🚑 Emergency Department (24/7 initiation).
• 🩺 Sexual Health / HIV clinics (risk assessment, follow-up, STI screening, prevention counselling).
• 👷 Occupational Health (healthcare and workplace exposures; review urgently).
• 🧾 SARC (Sexual Assault Referral Centre) where relevant.

4️⃣ 🧾 Immediate assessment checklist (do not delay PEP if indicated)

• 🕓 Exposure details: exact time, type, fluids involved, condom use/failure, ejaculation, trauma/bleeding, injury depth, device type (hollow-bore vs solid), visible blood.
• 🧑‍⚕️ Source assessment:
  • ✅ Known HIV status? On ART? Most recent viral load and date?
  • 🧪 If possible, arrange voluntary HIV testing of the source.
  • ⚡ Source results must not delay starting PEP when indicated.
  • 📝 Consent rules apply for source testing (follow local policy).
• 🤰 Patient factors: pregnancy potential, renal disease, hepatitis B status, drug interactions, current meds (including OTC/supplements), allergies.

5️⃣ 🧪 Baseline investigations (UK guideline set)

• All exposures (baseline):
  • 🧫 HIV 4th generation Ag/Ab test.
  • 🧊 Creatinine / eGFR (tenofovir safety; adjust if CrCl < 50 mL/min).
  • 🧪 ALT (baseline hepatic safety).
  • 🧬 Hepatitis B serology (HBsAg, anti-HBs, anti-HBc) unless documented immune.
  • 🤰 Pregnancy test where relevant.
• Sexual exposures (plus):
  • 🧷 STI testing per local pathway (chlamydia/gonorrhoea NAAT by site; syphilis serology).
  • 💊 Emergency contraception where appropriate.
• Hepatitis C testing 🔬:
  • Particularly for MSM condomless anal sex, PWID exposures, and occupational exposures.
  • For higher risk: consider HCV PCR/Ag early (shorter window than antibody) per local protocol.

6️⃣ 💊 Recommended PEP regimen (UK first-line)

⭐ First-line adult PEP (typical UK regimen):
Tenofovir disoproxil 245 mg / Emtricitabine 200 mg once daily
PLUS Raltegravir 1200 mg once daily
✅ Duration: 28 days

• 🧑‍🔬 Renal impairment: if CrCl < 50 mL/min, use an alternative NRTI backbone with specialist guidance.
• ⚠️ Interactions: verify meds (including OTC/supplements and recreational drugs).
• 🥛 Cations & raltegravir: antacids/iron/calcium/magnesium can reduce absorption - avoid or separate dosing as advised.

7️⃣ 🗣️ Counselling at initiation

• ⚡ Earlier is better - don’t wait.
• 🎯 Adherence is crucial (missed doses reduce effectiveness).
• 😵 Common side effects are usually mild and manageable.
• 🛡️ Use safer sex / risk reduction until follow-up testing is complete.
• 🧩 If ongoing risk, discuss transition to PrEP and link to sexual health services.

8️⃣ 😷 Side effects & safety monitoring

• 🤢 Nausea, 🥱 fatigue, 🤕 headache, 💩 diarrhoea.
• 🧪 Occasionally: abnormal LFTs or renal function changes.
• 📋 Repeat bloods during PEP only if baseline abnormal or symptoms occur.

9️⃣ 📅 Follow-up testing (UK approach)

• 🧫 Use a 4th-generation laboratory HIV assay.
• ✅ Final HIV test: at least 45 days after completing PEP (often aligned with 12-week STI follow-up in sexual health pathways).
• 🧬 Hepatitis B follow-up depends on immunity/vaccination status.
• 🔬 Hepatitis C follow-up for higher-risk exposures per local protocol (PCR/Ag may be used for earlier detection).
• 👷 Occupational exposure: ensure urgent Occupational Health review and documentation.

🔟 📈 Effectiveness

• ✅ PEP is highly effective when started early and taken correctly.
• ⏱️ Key determinants: time-to-start + adherence + correct risk stratification.

✅ Practical Do’s & Don’ts

• ✅ Start PEP immediately if indicated - don’t wait for source testing.
• ✅ Document exposure time precisely.
• ✅ Check interactions carefully (especially antacids/minerals with integrase inhibitors).
• ✅ Link to Sexual Health for STI screening and PrEP discussion.
• ⛔ Don’t prescribe PEP for negligible-risk exposures without specialist input.

📚 References (UK guidance)

• BHIVA/BASHH: UK Guideline for the use of HIV Post-Exposure Prophylaxis (PEP) (2021, with ongoing updates on BHIVA site).
• NICE NG60: HIV testing (service delivery and increasing uptake).
• UKHSA: Immunisation guidance (Green Book) for immunocompromised individuals.

🧠 Teaching note (pathophysiology)
HIV must establish local replication and then disseminate systemically; this takes time. PEP aims to block early replication during this “window of opportunity,” which is why starting within hours is so important. Think of it like treating bacterial meningitis: speed matters more than almost anything else. Your role is rapid risk assessment, immediate initiation when indicated, and reliable follow-up for HIV/STIs/hepatitis and prevention planning (including PrEP).