- Visual Analogue Scale (VAS) of pain is higher than 40 mm.
- Pain is sustained for more than 3 months after healing of herpes zoster skin rash.
- Malignancy within the past 2 years.
- Patients who have undergone neurolytic or neurosurgical therapy for postherpetic
- Creatinine clearance = 30 mL/min (estimated from serum creatinine, body weight, age,
and sex using the Cockcroft and Gault equation, by omitting any decimal fractions).
- Patients having other severe pain which may impair the self assessment of the pain due
to postherpetic neuralgia.
- Skin conditions in the affected dermatome that could alter sensation.