Summary of findings for the main comparison. Gabapentin compared with placebo for postherpetic neuralgia: efficacy.

Gabapentin compared with placebo for postherpetic neuralgia: efficacy
Patient or population: adults with postherpetic neuralgia Settings: community Intervention: gabapentin ≥ 1800 mg daily or gabapentin encarbil 1200 mg daily Comparison: placebo
Outcome	Probable outcome with gabapentin	Probable outcome with placebo	RR and NNT (95% CI)	Number of studies, participants	Certainty of the evidence (GRADE)	Comments
At least 50% reduction in pain or equivalent	330 per 1000	190 per 1000	RR 1.7 (1.4 to 2.0) NNT 6.9 (5.5 to 9.4)	7 studies 2031 participants	Moderate	Downgraded because of issues around dosing, formulation, and imputation
IMMPACT definition ‐ any substantial pain benefit	320 per 1000	170 per 1000	RR 1.8 (1.5 to 2.1) NNT 6.7 (5.4 to 8.7)	8 studies 2260 participants	Moderate	Downgraded because of issues around dosing, formulation, and imputation
Patient Global Impression of Change much or very much improved	390 per 1000	290 per 1000	RR1.3 (1.2 to 1.5) NNT 9.7 (6.9 to 16)	7 studies 2013 participants	Moderate	Downgraded because of issues around dosing, formulation, and imputation
IMMPACT definition ‐ any at least moderate pain benefit (includes Gong 2008 at 25% pain relief)	46 per 1000	25 per 1000	RR 1.8 (1.6 to 2.0) NNT 4.8 (4.1 to 6.0)	8 studies 2260 participants	Moderate	Downgraded because of issues around dosing, formulation, and imputation
CI: confidence interval; IMMPACT: Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials; NNT: number needed to treat for an additional beneficial outcome; RR: risk ratio
Descriptors for levels of evidence (EPOC 2015): High quality: this research provides a very good indication of the likely effect. The likelihood that the effect will be substantially different† is low. Moderate quality: this research provides a good indication of the likely effect. The likelihood that the effect will be substantially different† is moderate. Low quality: this research provides some indication of the likely effect. However, the likelihood that it will be substantially different† is high. Very low quality: this research does not provide a reliable indication of the likely effect. The likelihood that the effect will be substantially different† is very high. †Substantially different: a large enough difference that it might affect a decision.