In this study, the investigators aim to investigate the preventive efficacy of prophylactic oral duloxetine during acute herpes zoster on postherpetic neuralgia and its safety.

Postherpetic neuralgia is a common complication of herpes zoster. Several interventions have been investigated for the treatment of postherpetic neuralgia, however, there is a lack of preventive intervention on postherpetic neuralgia. A recent retrospective study revealed that the administration of gabapentin during the acute herpes zoster period significantly decreased the incidence of postherpetic neuralgia. In the present study, the investigators aim to conduct a prospective, randomized, open-label, endpoint blinded study to investigate the preventive efficacy of prophylactic use of duloxetine on postherpetic neuralgia.

Inclusion Criteria:

• ages more than 50 years;
• diagnosed with uncomplicated acute herpes zoster;
• presents with vesicles within 72 hours;
• has an average pain score of at least 40/100 mm on a visual analog scale (VAS, 0 = no pain, 100 = worst possible pain, at opposite ends of a 100-mm line).

Exclusion Criteria:

• refuses to participate or to provide written informed consent;
• Zung Self-Rating Depression Scale raw score of more than 50 points;
• herpes zoster that involves with head, neck, ocular, mucous membrane, cranial nerve, or central nervous system;
• has hemorrhagic or necrotizing lesions, satellite lesions, abnormal vesicles or acute retinal necrosis;
• has been on immunosuppressive therapy or mono- or multi-pharmacotherapy that involves any tricyclic antidepressant, valacyclovir, duloxetine or cytotoxic medications before acute HZ onset;
• has been diagnosed with hepatic, renal or immune dysfunction;
• during pregnancy or breastfeeding at the time;
• hypersensitivity to the study drugs;
• has contraindications to valacyclovir or duloxetine;
• HZ vaccinated.

The outcome of the study will be assessed by a third-party organization who will be blinded to the study allocation.