The inoculation of mice with herpes simplex virus type-1 (HSV-1) causes
herpes zoster-like skin lesions and
pain-related responses (
tactile allodynia and
mechanical hyperalgesia) from day 5 after inoculation. Skin lesions completely heal by day 15 after inoculation, but about half of mice with acute herpetic
pain show
pain-related responses long after the lesions heal. Using this mouse model, we examined the effects of repeated administration of
gabapentin and
amitriptyline on the acute herpetic
pain and the incidence of postherpetic
pain.
Gabapentin and
amitriptyline were administered three times daily from day 5 to 11 after inoculation. Postherpetic
pain-related responses were assessed on day 30 after inoculation.
Gabapentin (10-100 mg/kg) produced the dose-dependent inhibition of acute herpetic
pain-related responses. This medication produced marked reduction in the incidence of delayed postherpetic
pain and the dose of 100 mg/kg produced the complete inhibition.
Amitriptyline (10 mg/kg) did not affect the
acute pain-related responses in the initial 3- and 2-day periods and then gradually inhibited them. This dosage produced a substantial but non-significant decrease in the incidence of postherpetic
pain-related responses.
Amitriptyline (1 and 3 mg/kg) was without effects on acute herpetic and postherpetic
pain-related responses. The results strongly support the idea that the severity of the acute herpetic
pain is a risk factor of
postherpetic neuralgia. It may be worth testing the effects of
gabapentin on acute herpetic
pain and the incidence of
postherpetic neuralgia in human subjects.