Does gabapentin impact response to anticholinergics for overactive bladder?

It is unknown whether gabapentin modulates the therapeutic effect of anticholinergics (AC) in patients with overactive bladder. We hypothesized that pre-existing gabapentin use would improve response rates in these patients.

Female patients treated with AC between 2010-2018 were identified. Data were collected on gabapentin use, indication, dose and duration of use as well as demographic and clinical characteristics. Patients were stratified by those that only took AC and those that took both AC and gabapentin ("combination therapy"). Response was determined through chart review. Descriptive statistics were expressed as medians and interquartile ranges (IQR). Pairwise analysis was performed using Wilcoxon rank-sum. Multivariable logistic regression was used to identify independent variables predicting response. A subgroup analysis was performed in patients with chronic pain disorders.

Seven hundred fifty-six subjects met all criteria; 16.5% (n = 125) were on combination therapy. Those taking gabapentin were more likely to have chronic (49.6% vs. 22.5%, p < 0.001) or neuropathic pain (25.6% vs. 9.4%, p < 0.001) and to use narcotics (41.6% vs. 15.5%, p < 0.001). Patients taking combination therapy were not more likely to improve compared to patients taking AC alone (41.6% vs. 47.7%, p = 0.211), which persisted after adjusting for confounders (aOR = 1.02, 95% CI: 0.63-1.65). In the 182 patients with chronic pain, those receiving combination therapy were more likely to respond than those taking AC alone (35.2% vs. 21.9%, p = 0.0015), although this did not persist after adjusting for confounders (aOR = 1.15, 95% CI: 0.70-1.90).

Pre-existing gabapentin use does not seem to influence response to AC in patients with overactive bladder.