A 52-year-old man presents with severe, burning pain in the left T4 dermatome for 2 days, followed by the appearance of grouped vesicles on an erythematous base in the same distribution. He is otherwise healthy with no immunosuppression. Examination reveals crusting of some lesions. What is the most appropriate first-line antiviral therapy?

Explanation

## Diagnosis and Management of Herpes Zoster ### Clinical Presentation Recognition **Key Point:** The patient presents with classic herpes zoster: dermatomal distribution (T4), prodromal burning pain preceding vesicular eruption, and grouped vesicles on erythematous base with early crusting. ### First-Line Antiviral Selection **High-Yield:** For immunocompetent patients with acute herpes zoster, **valacyclovir** is the preferred first-line oral antiviral because: - Superior bioavailability compared to acyclovir (oral absorption ~55% vs 15–30%) - Achieves higher serum and CSF concentrations with less frequent dosing - Reduces pain duration and post-herpetic neuralgia (PHN) risk when started within 72 hours of rash onset - Better compliance due to three-times-daily dosing vs five-times-daily acyclovir **Clinical Pearl:** Oral valacyclovir 1 g TDS for 7–10 days is guideline-recommended for non-severe zoster in immunocompetent hosts [cite:Fitzpatrick's Dermatology 9e]. ### Comparative Antiviral Efficacy | Agent | Route | Dosing | Bioavailability | PHN Reduction | Use Case | |-------|-------|--------|-----------------|---------------|----------| | Valacyclovir | Oral | 1 g TDS × 7–10 d | 55% | ✓ Superior | **First-line (immunocompetent)** | | Famciclovir | Oral | 500 mg TDS × 7 d | 77% | ✓ Similar | Alternative if valacyclovir unavailable | | Acyclovir (oral) | Oral | 800 mg 5× daily × 7–10 d | 15–30% | ✓ Modest | Suboptimal due to dosing burden | | Acyclovir (IV) | IV | 10–15 mg/kg 8-hourly | 100% | ✓ Superior | Disseminated/CNS involvement or severe immunosuppression | | Penciclovir (topical) | Topical | 1% cream 6× daily | Minimal systemic | ✗ None | Adjunct only; does NOT prevent PHN | **Mnemonic:** **VAF** (Valacyclovir > Acyclovir > Famciclovir) for oral bioavailability and PHN prevention in immunocompetent zoster. ### Why Timing Matters **Key Point:** Antiviral therapy is most effective when started within **72 hours** of rash onset. This patient is within the window, making oral valacyclovir the standard choice. ### Adjunctive Management - Analgesics (paracetamol, NSAIDs, gabapentin) for pain control - Consider topical lidocaine patches for localized pain - Avoid topical antivirals alone (insufficient systemic penetration for PHN prevention)