Pregabalin versus gabapentin in the treatment of sciatica: Study protocol for a randomised, double-blind, cross-over trial (PAGPROS)

Abstract

Background: There is currently an absence of high-grade evidence regarding the treatment of chronic sciatica (CS). Whilst gabapentin (GBP) and pregabalin (PGB) are both currently used to treat CS, equipoise exists regarding their individual use. In particular, no head-to-head study of GBP and PGB in CS exists. Despite equipoise, most countries' formulary regulatory authorities typically favour one drug for subsidy over the other. This hinders interchange wherever the favoured drug is either ineffective or not tolerated. The primary aim of this study is to conduct a head-to-head comparison of the efficacy of PGB versus GBP for CS based on outcomes on a visual analogue scale (VAS) and the Oswestry Disability Index (ODI). Methods/design: We are conducting a prospective, randomised, double-blind, double-dummy cross-over study. Included patients will be over 18 years old and have unilateral CS with radiological confirmation of corresponding neural compression/irritation. Pregnant women, those with major organ disease, or those with creatinine clearance < 60 ml/minute will be excluded. Patients will continue their current pain medication at study onset, conditional upon dosage consistency during the prior 30 days. Each drug will be titrated up to a target dose (GBP 400-800 mg three times daily, PGB 150-300 mg twice daily) and taken for 8 weeks. The first drug will then be ceased; however, cross-over will be deferred pending a 1-week washout period. Drug efficacy will be assessed using the VAS and ODI. Results of the Health Locus of Control Scale and side effect frequency/severity will be used to determine psychological functioning. Assuming the hypothesis that PGB will display a superior effect, the sample size required is n = 38 with 80% power and a 5% type I error rate. Results will be analysed via intention-to-treat methodology. Discussion: This study will establish the efficacy of PGB compared with GBP in reducing pain in people with sciatica and lead to greater understanding of the treatment options available. Trial registration: Australian and New Zealand Clinical Trials Registry, 12613000559718. Registered on 17 May 2013.