Prophylactic Gabapentin Results in Dramatic Reduction of Narcotic Utilization in Head and Neck Cancer Patients Undergoing Radiotherapy

Abstract

A significant number of patients treated for head and neck cancer (HNC) develop pain from treatment requiring narcotic utilization. Pain mechanisms in HNC include both nociceptive and neuropathic components. Gabapentin (GP) was initially developed as an antiepileptic drug, but has proved as an effective treatment for neuropathic pain, increasingly in the oncologic setting. There have been several recent investigations into the use of GP in the multimodal management of HNC. While these early studies are promising, none has compared GP utilization during week 1 of radiotherapy (RT) or chemoradiotherapy (CRT) to a control group to evaluate impact on opioid requirement. Here we report a comparison of our opioid utilization comparing our GP cohort to a historical cohort treated prior to the routine utilization of GP. An institutional review board approved retrospective review of HNC patients treated December 2015-March 2019 with RT or CRT and prophylactic GP with a starting tapered regimen of 100mg-300mg three times daily (tid) during week 1 of therapy, with a max dose of 1200mg tid, escalated throughout treatment. This was compared to a control group of similarly matched historical cohort of 49 patients treated prior to GP being implemented. GP use, opioid use in morphine equivalent, pain score, mucositis, pharyngitis and dermatitis were recorded at each weekly on treatment visit and through-out follow-up evaluations. 139 patients from the GP arm and 49 patients from the historically matched control group were retrospectively analyzed after IMRT. Cohorts were well matched overall. Median gabapentin dose was 900mg tid. The absolute number of patients requiring any opioid pain medication was reduced by 50% in the GP cohort (77.6% vs. 38.9%), while still maintaining pain scores similar to those of patients historically treated with narcotics. Median difference in narcotic dose represented in morphine equivalents was significantly lower in the GP group at week 2 (p = .01) and remained significantly different until the last follow-up. On average, there was a 71.8% drop in nominal narcotic dose in the GP group compared to historical control. Adverse effects of gabapentin were minimal and reversed with stopping the medication. Reported fatigue scores were similar between groups. Overall PEG placement rate during radiation was 11.5% (15/130) as 9 patients had PEG tubes prior to starting radiation. Prophylactic GP can be can effectively and safely be administered to HNC patients undergoing RT or CRT and results in significant decrement in opioid requirement during treatment while achieving similar pain score improvement as narcotics. In the context of a global opioid crisis, these data would support GP as a widespread clinical standard in this patient population upon prospective validation of these findings.