What is the treatment for viral fever caused by herpes simplex virus (HSV) or varicella-zoster virus (VZV) with Acyclovir (antiviral medication)?

Treatment of Viral Fever with Acyclovir

Acyclovir should be administered immediately for viral fever caused by HSV or VZV, with intravenous acyclovir (10 mg/kg every 8 hours) for severe, disseminated, or immunocompromised cases, and oral acyclovir (800 mg five times daily) for uncomplicated herpes zoster or varicella in immunocompetent patients. 1, 2, 3

Immediate Initiation of Therapy

• Start acyclovir as soon as HSV or VZV infection is suspected, even before diagnostic confirmation, as early treatment (within 24-72 hours of symptom onset) significantly reduces morbidity and mortality 1, 4, 5
• For suspected herpes simplex encephalitis, initiate IV acyclovir immediately—mortality decreases from >70% untreated to 28% with treatment, and drops to 8% when started within 4 days of symptom onset 1
• In neutropenic patients with fever and suspected or confirmed cutaneous/disseminated HSV or VZV, acyclovir administration is strongly recommended 1

Dosing by Clinical Scenario

Intravenous Acyclovir Indications 2, 1, 5

Use IV acyclovir (10 mg/kg every 8 hours) for:

• Herpes simplex encephalitis (14-21 days duration) 1
• Neonatal HSV infection (20 mg/kg every 8 hours for 21 days) 1
• Immunocompromised patients with HSV or VZV infection 1, 2
• Disseminated varicella-zoster (multi-dermatomal or visceral involvement) 5, 2
• Severe initial genital herpes in immunocompetent patients 2
• Varicella in adults or immunocompromised children 6

Oral Acyclovir Indications 3, 5

Use oral acyclovir 800 mg five times daily for:

• Acute herpes zoster (shingles) in immunocompetent patients (7-10 days, continue until all lesions scab) 5, 3, 6
• Chickenpox (varicella) in persons ≥12 years or those with chronic conditions (80 mg/kg/day maximum 3,200 mg/day in 4 divided doses for 5 days, started within 24 hours of rash) 4, 3
• Initial or recurrent genital herpes 3

Critical Treatment Principles

Duration of Therapy 1, 5

• Continue treatment until all lesions have completely scabbed, not based on arbitrary calendar days 5
• For herpes simplex encephalitis: 14-21 days IV acyclovir 1
• For neonatal HSV: 21 days at higher dose (20 mg/kg every 8 hours) 1
• For herpes zoster: minimum 7-10 days, extending beyond if lesions remain active 5
• Consider repeat CSF PCR at end of therapy for encephalitis; if positive, continue treatment 1

Immunocompromised Patients 1, 5

• Always use IV acyclovir initially for immunocompromised patients with HSV or VZV infections 1, 5
• Consider temporary reduction in immunosuppressive medications during treatment of disseminated disease 5
• Monitor closely for dissemination, as these patients have higher risk of visceral complications 6
• Acyclovir-resistant strains may emerge; if lesions persist despite treatment, consider foscarnet 1, 7

Prophylaxis Considerations

When to Use Prophylactic Acyclovir 1

• Recurrent HSV/VZV: Daily oral acyclovir for patients with frequent severe recurrences 1
• Post-exposure varicella prophylaxis: If varicella-zoster immunoglobulin unavailable or >96 hours post-exposure, give 7-day course of oral acyclovir starting 7-10 days after exposure 5
• High-risk populations: Consider prophylaxis in patients receiving proteasome inhibitors, rituximab, high-dose steroids, or other intensive immunosuppression 1

Prophylaxis is NOT Routinely Recommended 1

• Universal HSV/VZV prophylaxis is not indicated for all immunocompromised patients 1
• Target prophylaxis to those with history of recurrent disease or receiving specific high-risk therapies 1

Important Clinical Caveats

Renal Function Monitoring 5, 6

• Maintain adequate hydration and urine flow during IV acyclovir therapy 6
• Adjust doses downward for impaired renal function 5, 6
• Monitor for thrombotic thrombocytopenic purpura/hemolytic uremic syndrome in immunocompromised patients on high-dose therapy 5

Treatment Limitations 5, 6

• Topical acyclovir is substantially less effective than systemic therapy and should not be used 5
• Acyclovir does not eradicate latent virus—it treats acute infection but cannot prevent future reactivations 4, 5
• Neither acyclovir nor other antivirals have been proven to prevent postherpetic neuralgia 6

Resistance Patterns 1, 7, 8

• Resistance remains rare in immunocompetent patients despite extensive use 8
• In severely immunosuppressed patients, acyclovir-resistant HSV occasionally emerges (typically thymidine kinase-deficient mutants) 8
• For acyclovir-resistant cases, switch to IV foscarnet 1, 7
• Resistance appears transient; subsequent recurrences typically involve sensitive virus 8

Special Populations 1, 4

• Neonates require higher doses (20 mg/kg every 8 hours for 21 days) to achieve adequate CNS penetration and reduce mortality to 5% 1
• Pregnant women: Acyclovir can be used when clinically indicated; zoster immunoglobulin is not contraindicated in pregnancy 1
• Facial/ophthalmic zoster: Requires urgent treatment due to risk of vision-threatening complications and cranial nerve involvement 5