Urinary Incontinence Induced by Tramadol

Sir,

Tramadol is a centrally acting opioid analgesic; it is a μ-receptor agonist and inhibits reuptake of serotonin and norepinephrine.[1] The antimuscarinic effect of tramadol is helpful in patients with detrusor overactivity;[2] however, urinary incontinence has not been mentioned as a side effect associated with tramadol use.

A 63-year-old female presented in our pain clinic with cancer pain secondary to carcinoma buccal mucosa; we prescribed a combination of acetaminophen (325 mg) with tramadol (37.5 mg) q.i.d. However, the patient complained of urinary incontinence while sleeping in the night two days after starting this treatment. The postvoided residue was nil in this case, which delineated the possibility of overflow incontinence; in addition, there was no past history of urinary incontinence. Incontinence disappeared after treatment was stopped. We encountered similar problem in 3-4 patients in the elderly age-group.

Tramadol decreases pelvic floor electromyography (EMG) activity; the possible explanation is modulation of proprioceptive afferent inputs from the pelvic floor by tramadol at the dorsal horn level, which are important in maintaining muscle tone, and hence EMG activity.[3] Literature also suggests presence of prejunctional serotonin receptors at parasympathetic nerve terminals in the human bladder.[4] These receptors are involved in both positive (5-HT4 and 5-HT7) and negative (5-HT1A) feedback mechanisms regulating cholinergic transmission; activation of excitatory serotonin receptors may cause reflex relaxation of the urethral sphincter along with detrusor contraction. Thus, parasympathetic hyperactivity with pelvic floor relaxation might have contributed to urinary incontinence in these cases. Hence, possibility of urinary incontinence should always be kept in mind while using tramadol, especially in population prone to urinary incontinence. However, molecular studies of greater magnitude investigating the pelvic floor neurophysiology are required.