A 32-year-old woman from Mumbai presents with a 3-day history of severe vesicular rash in a dermatomal distribution over the left thoracic region. She reports intense burning pain and fever (38.5°C). Examination reveals grouped vesicles on an erythematous base, some already crusting. She has no prior history of chickenpox but received varicella vaccination 15 years ago. What is the most appropriate antiviral therapy for this patient?

Explanation

## Clinical Diagnosis The patient presents with classic herpes zoster (shingles): dermatomal vesicular eruption with severe pain and systemic symptoms in an immunocompetent host. ## Antiviral Selection for Herpes Zoster **Key Point:** Valacyclovir and famciclovir are the preferred agents for herpes zoster in immunocompetent patients because they achieve higher intracellular acyclovir triphosphate concentrations and require less frequent dosing than acyclovir. **High-Yield:** Valacyclovir is the L-valyl ester prodrug of acyclovir; it has superior oral bioavailability (~54% vs 15–20% for acyclovir) and is converted to acyclovir by first-pass hepatic metabolism. ## Comparison of Nucleoside Analogues for Zoster | Agent | Dosing (Zoster) | Bioavailability | Frequency | Clinical Use | |-------|-----------------|-----------------|-----------|---------------| | Acyclovir | 800 mg 5× daily | 15–20% | QID–5× daily | Mild zoster; IV for severe/disseminated | | Valacyclovir | 1000 mg 3× daily | ~54% | TDS | **First-line for immunocompetent zoster** | | Famciclovir | 500 mg 3× daily | ~77% | TDS | Alternative first-line; similar efficacy | | Ganciclovir | IV only | — | BD | CMV; not indicated for VZV in immunocompetent | **Clinical Pearl:** In immunocompetent patients with zoster, valacyclovir and famciclovir reduce pain duration and post-herpetic neuralgia (PHN) incidence more effectively than oral acyclovir, making them preferred agents [cite:Harrison 21e Ch 187]. ## Treatment Principles 1. **Timing:** Initiate within 72 hours of rash onset (this patient is at day 3—still within window). 2. **Duration:** 7 days standard for immunocompetent hosts. 3. **Adjuncts:** Consider analgesics (NSAIDs, gabapentin) for pain control. **Mnemonic:** **VAL-FAM-ACY** — *Valacyclovir and Famciclovir are first-line; Acyclovir is older, less frequent dosing with newer agents.*