A trial included a total of 56 subjects with diabetic polyneuropathy or postherpetic neuralgia. They received daily oral gabapentin, nortriptyline, and their combination. In sequence, a different drug was given to each randomised group in 3 treatment periods. During each 6-week treatment period, drug doses were titrated towards maximum tolerated dose. Mean daily pain (0—10) was 5.4 (95% CI 5.0 to 5.8) at baseline, and at maximum tolerated dose, pain was 3.2 (2.5 to 3.8) for gabapentin, 2.9 (2.4 to 3.4) for nortriptyline, and 2.3 (1.8 to 2.8) for combination treatment. Pain with combination treatment was significantly lower than with gabapentin (−0.9, 95% CI −1.4 to −0.3) or nortriptyline alone (−0.6, 95% CI −1.1 to −0.1). At maximum tolerated dose, the most common adverse event was dry mouth, which was significantly less frequent in patients on gabapentin than on nortriptyline or combination treatment.
Comment: The quality of evidence is downgraded by imprecise results (one small trial).