Assessment of Pain Quality in a Clinical Trial of Gabapentin Extended Release for Postherpetic Neuralgia

Objective: To replicate and extend previous research concerning the validity and utility of using pain quality measures in clinical trials. Methods: One hundred fifty-eight patients with moderate-to-severe postherpetic neuralgia were randomly assigned to I of 3 treatment conditions: (1) extended release gabapentin (G-ER) 1800 mg once-daily administered in the evening; (2) G-ER 1800 mg asymmetric divided dose (600 mg ANI and 1200 mg PM); or (3) placebo G-ER. A measure of different pain qualities. the Neuropathic Pain Scale, was administered as a secondary measure in this study before, during, and after the treatment. Results: The results suggest that G-ER, especially when administered twice-daily, have the greatest effects on sharp, dull, sensitive, and itchy pain. Few between-condition effects were found for the global ratings of intensity or unpleasantness, and for hot, cold, deep, or surface pain qualities. Conclusions: The results provide further Support for the importance of assessing specific pain qualities as outcomes in clinical trials. The findings may also be used by clinicians for identifying those patients for whom G-ER may be particularly effective, that is, patients with postherpetic neuralgia presenting with pain described as sharp, dull, sensitive, or itchy.