GaPP: a pilot randomised controlled trial of the efficacy of action of gabapentin for the management of chronic pelvic pain in women: study protocol

Introduction Chronic pelvic pain (CPP) affects >1 million UK women. Annual healthcare costs are estimated at >£150 million. Proven interventions for CPP are limited, and treatment is often unsatisfactory. Gabapentin is increasingly prescribed due to reports of effectiveness in other chronic pain conditions, but there are insufficient data supporting value in CPP specifically. The mechanism by which gabapentin exerts its analgesic action is unknown. Given the prevalence and costs of CPP, the authors believe that a large, multicentre, placebo-controlled, double-blind randomised controlled trial to evaluate the efficacy of gabapentin in management of CPP is required. The focus of this study is a pilot to inform planning of a future randomised controlled trial. Methods and analysis The authors plan to perform a two-arm, parallel, randomised controlled pilot trial. The authors aim to recruit 60 women with CPP in NHS Lothian and NHS Grampian (UK) and randomise them to gabapentin or placebo. Response to treatment will be monitored by questionnaire compared at 0, 3 and 6 months. The primary objective is to assess recruitment and retention rates. The secondary objectives are to determine the effectiveness and acceptability to participants of the proposed methods of recruitment, randomisation, drug treatments and assessment tools and to perform a pretrial cost-effectiveness assessment of treatment with gabapentin. Ethics and dissemination Ethical approval has been obtained from the Scotland A Research Ethics Committee (LREC 12/SS/0005). Data will be presented at international conferences and published in peer-reviewed journals. Trial registration number ISRCTN70960777.
Article summary Article focus Is it possible to achieve acceptable recruitment and retention rates in a two-arm, parallel, randomised controlled pilot trial of women with CPP given gabapentin and placebo? Are the proposed methods of recruitment, randomisation, drug treatments and assessment tools in this pilot trial effective and acceptable to participants? Is gabapentin likely to be cost effective for the management of CPP in women given the current level of uncertainty? Key messages CPP affects >1 million UK women, and treatments are often unsatisfactory. Gabapentin is being increasingly prescribed due to reports of effectiveness in other chronic pain conditions, but there are insufficient data supporting its value in CPP specifically. A large, multicentre, placebo-controlled, double-blind randomised controlled trial (RCT) to evaluate the efficacy of gabapentin in management of CPP is required. The focus of this study is a pilot to inform planning of a future RCT. Strengths and limitations of this study We recognise that there may be potential difficulties in mounting a large RCT for a chronic pain condition using gabapentin (a medication with known sedating side effects). We have designed this pilot study to assess practical feasibility. The study has been designed following the ‘Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials’ recommendations for the design of chronic pain clinical trials. Gabapentin requires titration to achieve an efficacious dose so that the rate and severity of adverse effects are minimised. We have included focus group assessment of the acceptability of the drug treatment and titrating regime in our study to inform the design of the future RCT. We plan to use a wide range of data collection tools in our study, but it is our intention to use fewer in our future RCT depending on their effectiveness in the pilot study (defined by lack of missing data, ability to detect effect and independence) and participant feedback on acceptability.