Early Pain Reduction Can Predict Treatment Response: Results of Integrated Efficacy Analyses of a Once‐Daily Gastroretentive Formulation of Gabapentin in Patients with Postherpetic Neuralgia

Objective.  The objectives of this study were to identify and determine the validity of early decision criteria following once‐daily gastroretentive gabapentin (G‐GR) treatment in patients with postherpetic neuralgia (PHN). Design.  In two placebo‐controlled studies, 279 patients were randomized to 1,800 mg G‐GR and 270 to placebo with the evening meal; patients underwent a 2‐week dose titration, followed by 8 weeks of stable dosing, and 1 week of dose tapering. Patients.  Adults with PHN for ≥6 months and an average baseline Numerical Pain Rating Scale (NPRS) score of ≥4 were included in the study. Outcome Measures.  Percent change from baseline to week 10 in NPRS scores and the percentage of responders (defined as ≥30% reduction in NPRS scores from baseline to week 10) were determined. Methods.  Patients randomized to G‐GR were categorized at each week based on their percent pain reduction up to that week, and for each category, the percentage of week 10 responders was computed. For several early‐improvement criteria, the percentage of week 10 responders, odds ratios for achieving week 10 treatment response, sensitivity, and specificity were calculated. Results.  There was a significant positive association between early pain reduction and week 10 treatment response. Pain reduction of <10% at week 5 of G‐GR treatment was the best early predictor of lack of endpoint response, with only 8% of these patients moving on to become week 10 treatment responders. Conclusions.  Early response was a reliable predictor of final response. This approach holds promise for aiding clinicians in decision making regarding the need for alternative or supplemental treatment during G‐GR therapy for PHN.