What oral acyclovir dose should I start for an 80‑year‑old with a one‑week‑old shingles rash and still‑uncrusted lesions, assuming adequate renal function?

Acyclovir Dosing for One-Week-Old Shingles with Uncrusted Lesions

For an 80-year-old with a one-week-old shingles rash and still-uncrusted lesions, start oral acyclovir 800 mg five times daily and continue until all lesions have completely scabbed—not for a fixed 7-day period. 1, 2

Treatment Rationale Despite Late Presentation

• The 72-hour treatment window applies to optimal efficacy, but antiviral therapy should still be initiated when lesions remain active beyond one week. 1, 2
• The critical endpoint is complete crusting of all lesions, not calendar days from rash onset. 1, 2
• Active vesicular or ulcerative lesions indicate ongoing viral replication, making antiviral therapy beneficial even after the traditional 72-hour window. 1, 2
• In elderly patients (≥80 years), the risk of postherpetic neuralgia is substantially elevated, providing additional justification for late antiviral initiation. 3

Specific Dosing Regimen

• Acyclovir 800 mg orally five times daily (every 4 hours while awake) is the standard dose for herpes zoster. 1, 2, 4
• Continue treatment until all lesions have completely scabbed—this may require 10–14 days or longer in elderly patients. 1, 2
• Do not discontinue therapy at exactly 7 days if lesions remain uncrusted; the clinical endpoint (complete scabbing) supersedes arbitrary duration. 1, 2

Mandatory Renal Assessment Before Initiation

• In an 80-year-old patient, measure creatinine clearance before starting acyclovir to determine whether dose adjustment is required. 2
• Acyclovir is renally eliminated and can cause crystalluria and acute renal failure, particularly in elderly patients with age-related renal decline. 2
• Dose adjustments are mandatory for creatinine clearance <50 mL/min to prevent neurotoxicity and renal injury. 2
• Ensure adequate hydration during therapy to minimize the risk of acyclovir-induced nephropathy. 2

Alternative Oral Antivirals with Superior Convenience

• Valacyclovir 1000 mg three times daily for 7–10 days (until complete crusting) offers superior bioavailability and less frequent dosing than acyclovir. 1, 2, 3
• Famciclovir 500 mg three times daily for 7–10 days is equally effective and may improve adherence compared with five-times-daily acyclovir. 1, 2, 5
• Both valacyclovir and famciclovir require renal dose adjustment in elderly patients with impaired creatinine clearance. 2

Indications for Intravenous Acyclovir in This Patient

• Switch to IV acyclovir 10 mg/kg every 8 hours if the patient has disseminated disease (≥3 dermatomes, visceral involvement, or hemorrhagic lesions). 1, 2
• IV therapy is required for complicated facial zoster with suspected cranial-nerve involvement, CNS complications (encephalitis, meningitis), or ophthalmic disease. 1, 2
• If lesions fail to improve or new lesions continue to appear after 7–10 days of adequate oral therapy, suspect acyclovir resistance and switch to IV acyclovir with resistance testing. 1, 2
• Severely immunocompromised patients (active chemotherapy, organ transplant, HIV with low CD4 count) should receive IV acyclovir even when disease appears localized. 1, 2

Monitoring During Treatment

• Expect clinical improvement (cessation of new lesions, reduction in pain) within 48–72 hours of starting therapy. 1
• If lesions persist or new lesions appear after 7–10 days of treatment, obtain viral culture with susceptibility testing to rule out acyclovir resistance. 1, 2
• For confirmed acyclovir-resistant VZV, switch to foscarnet 40 mg/kg IV every 8 hours until clinical resolution. 1, 2
• Resistance is rare in immunocompetent patients (<0.5%) but occurs in up to 7% of immunocompromised individuals. 1, 2

Common Pitfalls to Avoid

• Do not apply the 24-hour treatment window for varicella (chickenpox) to herpes zoster, which has a 72-hour window—but do not withhold therapy beyond 72 hours if lesions remain active. 1
• Do not stop acyclovir at exactly 7 days if lesions have not fully scabbed; continue until the clinical endpoint is reached. 1, 2
• Do not use the genital-herpes dosing regimen (400 mg three times daily) for shingles; the VZV-appropriate dose is 800 mg five times daily. 1, 2
• Do not use topical acyclovir for shingles; it is substantially less effective than systemic therapy. 1, 2
• Do not delay IV escalation in immunocompromised patients, even when disease appears localized. 1, 2

Adjunctive Pain Management

• Gabapentin titrated to 2400 mg daily in divided doses is first-line therapy for acute zoster-associated neuropathic pain. 2
• Over-the-counter analgesics (acetaminophen, ibuprofen) and topical cold packs can reduce acute pain during the vesicular phase. 2
• An 8% capsaicin patch applied once provides analgesia lasting at least 12 weeks for chronic neuropathic pain, but should not be applied to active vesicular lesions. 2

Infection Control Until Complete Crusting

• The patient remains contagious until all lesions have fully crusted and should avoid contact with susceptible individuals (pregnant women, immunocompromised persons, infants). 1, 2
• Cover lesions with clothing or dressings to minimize transmission risk via direct contact or aerosolized vesicular fluid. 2

Vaccination After Recovery

• Administer the recombinant zoster vaccine (Shingrix) after complete recovery to prevent future recurrences, regardless of this prior episode. 2
• Shingrix provides >90% efficacy in preventing future herpes zoster and is recommended for all adults ≥50 years. 2