Overactive bladder (OAB) syndrome as defined by International Continence Society is a pathological condition characterized by irritative symptoms: urinary urgency, with or without incontinence, urinary frequency and nocturia. The syndrome often seriously compromises the quality of life of the patients. The etiology of the OAB is considered multifactorial. Neural plasticity of bladder afferent pathways is one of the proposed mechanisms of OAB. The detrusor muscle itself has for many years been the target for drug treatment such as antimuscarinics. However, depression of detrusor contractility, may results in a reduced ability to empty the bladder and lead to some sympathetic adverse effects, which limits the treatment of OAB. Currently the focus of OAB treatment has changed to other bladder structures/mechanisms, such as afferent nerves and urothelial signaling as targets for intervention. C-fiber bladder afferents nerves may be critical for symptom generation in pathologic states such as OAB because these fibers demonstrate remarkable plasticity. Up-regulation of bladder C-fiber afferent nerve function may also play a role in urge incontinence, overactive bladder (OAB) and sensory urgency. The mechanism of Gabapentin's action for neuropathic pain has not been fully elucidated but is appears to have inhibitory activity on afferent C-fibers nerve activity; moreover, several studies had established the safety of Gabapentin in its treatment of different conditions. Due to the proposed mechanism, the investigators suggest that Gabapentin may be a new alternative for treating OAB.