Gabapentin for Postop Pain After SSLF

Pelvic organ prolapse (POP), the herniation of the bladder, uterus, or rectum, into and often beyond, the vaginal opening, affects 40% of postmenopausal women, and significantly impairs quality of life. POP is often managed surgically, and currently, one in every eight women will undergo POP surgery during her lifetime.

A commonly performed procedure for POP is a sacrospinous ligament fixation (SSLF), which is a vaginal surgery that involves suspending the vaginal apex to the sacrospinous ligament suspension with sutures. Beyond routine postoperative pain, a SSLF may result in significant gluteal pain as a result of the vaginal sutures affecting/impinging on the sacral nerve roots. Unfortunately, postoperative gluteal pain is not uncommon with 12% of patients reporting significant gluteal pain and 4% having persistent pain 6 weeks after surgery.

The aim of this study is to compare the impact of gabapentin versus placebo on postoperative pain after SSLF. The rationale is that studies have shown that preoperative gabapentin, a non-opioid analgesic, resulted in a lower narcotic use postoperatively. Decreasing use of standard of care postoperative narcotic pain medications would also decrease adverse events due to narcotics such as nausea, vomiting and constipation, and potentially decrease the long-term risk of opioid dependence. As an additional benefit, a careful assessment of actual opioid will help to inform best practices for prescribing, as it is possible that we are overprescribing narcotic medications for this type of surgery. This study will evaluate a longer two-week course of gabapentin because it is currently standard of care to use gabapentin to treat neuropathic pain after SSLF; thus, gabapentin may help to address overall pain as well as neuropathic gluteal pain that can occur after SSLF. Furthermore, gabapentin is a relatively safe medication with the primary adverse events being dizziness and sedation.

An exploratory component of this study will be a pharmacogenetics aim for narcotic use. It is known that genetic variability in drug metabolizing enzymes may impact the response to opioids. For example, poor metabolizers may not convert opioids to their active forms resulting in less pain relief and potentially higher doses of medications. Conversely those who are fast metabolizers may have higher levels of active forms and thus require lower doses of narcotics. One well-characterized cytochrome P450 (CYP) enzyme is CYP2D6, which metabolizes commonly used opioids such as codeine, tramadol, hydrocodone and oxycodone. The CYP2D6 gene has several genetic variants, which result in different metabolizer statuses ranging from poor metabolizers (PM), intermediate metabolizers (IM), extensive metabolizers (EM), to ultrarapid metabolizers (UM). These different CYP2D6 profiles may be clinically important for opioid use, as they may contribute to the variability in efficacy and adverse events to these drugs. Because this study will provide detailed information about narcotic use, this will be an ideal study for this exploratory pharmacogenetics analysis.

Given the risk of overall postoperative pain and neuropathic gluteal pain after a SSLF for POP and the evidence that perioperative gabapentin may decrease acute pain and neuropathic pain, this study proposes a novel randomized trial to compare perioperative gabapentin versus placebo on postoperative pain after a vaginal SSLF surgery.