Efficacy and Tolerability of Solifenacin Combined With Gabapentin Versus Solifenacin Monotherapy for the Treatment of Non-neurogenic Overactive Bladder in Women: A Randomized Controlled Trial

Overactive bladder (OAB) syndrome is defined as a pathological condition characterized by urinary urgency, with or without incontinence, urinary frequency and nocturia in the absence of infection or other identifiable pathology. Global prevalence among women is estimated to be 21.9% with even higher prevalence among Egyptian women suggested to be around 57%. The pathophysiology of overactive bladder is incompletely understood. The underlying mechanism behind OAB symptoms is often detrusor overactivity (DOA), which has been linked to bladder ischemia and oxidative stress. Also, it is believed to be related to dysfunction within the nervous system, ranging from cortical and brainstem command centers to afferent signaling at the urothelial level. Also it is may be related to spontaneous activity in the detrusor muscle which can lead to involuntary contractions and urgency sensations, even without abnormal nerve stimulation. Antimuscarinic agents, such as solifenacin, are considered first-line pharmacological therapy after failure of conservative measures. However, the efficacy as a monotherapy is limited, and many patients experience persistent symptoms. Therefore, combination therapy using antimuscarinics and other agents such as B3 agonists has been proven to have more efficacy compared to monotheraрy.

Currently the focus of OAB treatment has changed to other bladder structures and mechanisms, such as modulation of bladder afferent outflow and urothelial signaling as targets for intervention. Gabapentin, a neuromodulator commonly used for neuropathic pain, has shown potential benefits in bladder hypersensitivity and sensory urgency due to its inhibitory effect on afferent C fiber activity, as these fibers demonstrate remarkable plasticity, which is involved in the micturition reflex to the spinal tract. Several randomized controlled trials and cohort studies have demonstrated some improvement in OAB symptoms with minimal adverse effects following gabapentin administration, supporting its potential use as a treatment for OAB. However, the vast majority of studies are done in neurogenic bladder, had relatively small sample sizes and modest treatment effects, and only very few studies are done in non-neurogenic bladders.

In this study, it is assumed that combination therapy of solifenacin and gabapentin may provide synergistic effects, improving both detrusor overactivity and sensory urgency, leading to better patient outcomes than solifenacin monotherapy.