What is the recommended dosing for post-HIV (Human Immunodeficiency Virus) prophylaxis?

Post-HIV Exposure Prophylaxis Dosing

The recommended basic regimen for post-HIV exposure prophylaxis is Zidovudine (ZDV) 600 mg per day in two or three divided doses plus Lamivudine (3TC) 150 mg twice daily (available as COMBIVIR™ as a single tablet twice daily) for 28 days, initiated within 72 hours of exposure. 1

Basic Regimen (First-Line)

Zidovudine (ZDV/AZT) + Lamivudine (3TC): 1

• ZDV: 600 mg per day, divided into two or three doses
• 3TC: 150 mg twice daily
• Available as COMBIVIR™: Single tablet twice daily for improved adherence 1

Why This Regimen Is Preferred:

• ZDV is the only agent with demonstrated decreased risk of HIV transmission in CDC case-control studies of occupational HIV infection 1
• Most extensively used for PEP in healthcare personnel with established safety profile 1
• Serious toxicity is rare when used for PEP 1
• Considered safe for pregnant healthcare workers 1

Important Caveats:

• Side effects (nausea, fatigue) are common but manageable with antimotility and antiemetic agents 1
• Source patient virus may have resistance to this regimen—consider resistance testing if available 1

Alternate Basic Regimens

Option 1: Lamivudine + Stavudine 1

• 3TC: 150 mg twice daily
• d4T: 40 mg twice daily (30 mg twice daily if body weight <60 kg)
• Advantages: Well tolerated with good adherence, serious toxicity rare 1

Option 2: Didanosine + Stavudine 1

• ddI: 400 mg daily on empty stomach (125 mg twice daily if body weight <60 kg)
• d4T: 40 mg twice daily (30 mg twice daily if body weight <60 kg)
• Use when: Source patient is taking ZDV and 3TC (likely effective against resistant strains) 1
• Critical warning: Monitor closely for pancreatitis, lactic acidosis, and hepatitis—fatal pancreatitis has occurred 1

Expanded Regimen (For High-Risk Exposures)

Add ONE of the following to the basic regimen: 1

Indinavir (IDV) 1

• Dose: 800 mg every 8 hours on empty stomach
• Critical requirement: Must drink 8 glasses of fluid per day to prevent nephrolithiasis 1
• Avoid: During late pregnancy due to hyperbilirubinemia 1

Nelfinavir (NFV) 1

• Dose: 750 mg three times daily with meals OR 1250 mg twice daily with meals
• Drug interactions: Avoid concomitant use with astemizole, terfenadine, ergot derivatives, cisapride, St. John's Wort, lovastatin, simvastatin, pimozide, midazolam, triazolam 1
• Women: May accelerate clearance of oral contraceptives—use alternative contraception 1

Efavirenz (EFV) 1

• Dose: 600 mg daily at bedtime
• Contraindicated: In pregnancy due to teratogenicity concerns 1
• Common side effects: Dizziness, somnolence, insomnia, abnormal dreaming; severe psychiatric symptoms possible 1
• Serious risk: Stevens-Johnson syndrome (rare) 1

Abacavir (ABC) 1

• Dose: 300 mg twice daily (available as TRIZIVIR™ with ZDV and 3TC)
• Critical warning: Severe hypersensitivity reactions can occur, usually within first 6 weeks 1

Critical Implementation Details

Timing and Monitoring 1

• Initiate PEP: Within 72 hours of exposure (sooner is better)
• Duration: 28 days
• Evaluate within 72 hours: Assess for drug toxicity
• Monitor: For at least 2 weeks for drug toxicity 1

Follow-Up Testing 1

• HIV antibody testing: At baseline, 6 weeks, 3 months, and 6 months
• Test immediately: If symptoms compatible with acute retroviral syndrome occur
• Precautions: Advise exposed persons to prevent secondary transmission during follow-up period 1

Modern Evidence Considerations

While the guidelines provided are from 2001, more recent research supports newer regimens with improved completion rates:

• Elvitegravir/cobicistat/TDF/FTC (Quad pill): Single daily pill with 71% completion rate versus 57% for TDF/FTC + raltegravir and 39% for older regimens 2
• Dolutegravir + TDF/FTC: 90% completion rate with once-daily dosing, well tolerated 3

However, in the absence of updated formal guidelines in your evidence set, the CDC 2001 recommendations remain the official standard, with ZDV + 3TC as the basic regimen due to its proven efficacy in reducing HIV transmission risk. 1

Common Pitfalls to Avoid

• Do not delay: PEP must start within 72 hours; efficacy decreases with time 1
• Do not use efavirenz in pregnancy or women of childbearing potential without reliable contraception 1
• Monitor renal function with ddI + d4T combination due to serious toxicity risk 1
• Ensure adequate hydration (8 glasses/day) with indinavir to prevent kidney stones 1
• Check drug interactions especially with protease inhibitors and efavirenz 1