From the Guidelines
Cyclobenzaprine (Flexeril) is unlikely to cause polyuria (increased urination) as it typically exhibits anticholinergic effects that lead to urinary retention, not increased urination. The medication's primary action as a skeletal muscle relaxant and its structural relation to amitriptyline contribute to its anticholinergic properties, which can cause effects such as constipation, dry mouth, and notably, urinary retention 1. Although the exact mechanisms of cyclobenzaprine on the urinary system are complex and involve both central and peripheral anticholinergic activity, the predominant effect observed is urinary retention, not polyuria.
Key points to consider regarding the side effects of cyclobenzaprine include:
- Anticholinergic effects such as hallucinations, confusion, drowsiness, constipation, urinary retention, and dry mouth 1
- Potential for interaction with sedatives and anesthetic agents
- Risk of withdrawal symptoms like malaise, nausea, and headache upon discontinuation, which can be mitigated by tapering the medication over 2 to 3 weeks 1
- Concomitant use with monoamine oxidase inhibitors may increase the risk of serotonin syndrome
Given the information from the most recent and highest quality study available 1, it's crucial to prioritize the patient's overall clinical presentation and medical history when assessing the likelihood of cyclobenzaprine causing polyuria. If a patient on cyclobenzaprine reports increased urination, it's essential to investigate other potential causes, such as urinary tract infections or other conditions that may require medical attention, rather than attributing the symptom solely to the medication.
From the FDA Drug Label
Urogenital: Urinary frequency and/or retention. The answer is yes, Cyclobenzaprine (Flexeril) can cause polyuria (increased urination), as indicated by the term "urinary frequency" in the drug label 2.
From the Research
Cyclobenzaprine and Polyuria
- There is no direct evidence in the provided studies that suggests Cyclobenzaprine (Flexeril) causes polyuria (increased urination) 3, 4, 5, 6, 7.
- The studies primarily focus on the pharmacokinetics, efficacy, and tolerability of Cyclobenzaprine in various formulations and dosages, without mentioning its effects on urination frequency 3, 5, 6, 7.
- One study examines the effects of Cyclobenzaprine on urethral sensation and neuromuscular function, but it does not report any changes in urination frequency 4.
- The lack of relevant data suggests that there is no conclusive evidence to determine whether Cyclobenzaprine causes polyuria 3, 4, 5, 6, 7.