Four trials were included in the review. One trial evaluated gabapentin (n=150 patients). Three trials evaluated pregabalin (n=2,022 patients). Quality scores ranged from 6 to 8 (not fully explained with Jadad criteria); methodological limitations were noted.
600mg pregabalin daily: For patients who received 600mg of pregabalin per day, response to treatment was significantly higher compared with placebo (OR 1.70, 95% CI 1.27 to 2.29; I2=12.9%; two trials; NNT 8 patients, 95% CI 6 to 19). The active treatment group had significantly fewer drop-outs due to lack of efficacy (OR 0.19, 95% CI 0.09 to 0.4; I2=2.7%; two trials), but drop-outs due to adverse events were higher in the pregabalin group than placebo (OR 3.57, 95% CI 2.4 to 5.31; I2 =1.6%; two trials; NNH 6, 95% CI 4 to 9).
450mg pregabalin daily: Treatment response was significantly higher for patient who received 450 mg of pregabalin compared with placebo (OR 1.92, 95% CI 1.49 to 2.12; I2=46.3%; three trials; NNT 7, 95% CI 5 to 11). Drop-outs due to lack of efficacy were lower in this group than placebo (OR 0.3, 95% CI 0.18 to 0.51; I2=0; three trials). Drop-outs due to adverse events were higher in the pregabalin group than placebo (OR 2.28, 95% CI 1.58 to 3.29; I2=0; three trials; NNH 11, 95% CI 7 to 23).
300mg pregabalin daily: Treatment response was higher for this group than placebo (OR 1.53, 95% CI 1.18 to 1.98; I2=0; three studies; NNT=11, 95% CI 7 to 28). Drop-outs due to lack of efficacy were lower in the pregabalin group than placebo (OR 0.36, 95% CI 0.22 to 0.59; I2=0; three trials). Drop-outs due to adverse events were higher in the pregabalin group than placebo (OR 1.65, 95% CI 1.12 to 2.42; I2=0%; three trials; NNH =10, 95% CI 10 to 99).
Pregabalin adverse events: Risks of dizziness, somnolence, dry mouth, weight gain, and peripheral oedema were significantly higher in the pregabalin group compared with placebo, for all three doses of pregabalin.
Gabapentin: Compared with placebo, one trial of gabapentin showed significantly higher response to treatment compared to placebo. Risk of dizziness, sedation, light-headedness, and weight gain were reported significantly more in patients who received gabapentin.
There were no significant differences between drug doses in the indirect comparison and sensitivity analyses, although 450mg pregabalin showed a higher treatment response than 300mg.
Publication bias was not reported.