Is urinary retention reported as an adverse drug reaction to venlafaxine (Efexor depot) or mirtazep

Fråga: Is urinary retention reported as an adverse drug reaction to venlafaxine (Efexor depot) or mirtazepine (Remeron)?

The question relates to a 25-year-old previously healthy male on no other medication. He was treated with venlafaxine 75mg daily for depression and 6 days after initiation of treatment he was admitted to the hospital with sudden onset of urinary retention. A switch to mirtazepine is under consideration.

Sammanfattning: Urinary retention is a rare adverse drug reaction to both venlafaxine and mirtazapine. In the present case it is difficult to evaluate the fact that sudden onset of urinary retention occurred and what importance this may have in predicting the outcome of a switch to mirtazapine. A similar reaction to mirtazepine is possible and can not be excluded.

Svar: The files of the Swedish Adverse Drug Reactions Advisory Committee contain five reported cases of urinary retention per 25 million DDD for venlafaxine and one report per 15 million DDD for mirtazapine (1). In two case reports venlafaxine in combination with SSRIs was suspected to cause urinary retention (2,3). In both cases there was also a history of benign prostatic hypertrophy. The urinary problems associated with the tricyclic antidepressants are usually ascribed to their anticholinergic effects (4). Venlafaxine and the SSRIs have a low to very low affinity to muscarinic receptors but it is possible that in a patient with a pre-existing prostatic hypertrophy, this may be sufficient to cause side effects (2). In one of the reports it is discussed whether increased levels of serotonin might affect the bladder via central mechanisms (3). The pharmacodynamic properties of venlafaxine and mirtazapine are slightly different but the final result in both cases is an increased activity at serotonin and noradrenaline-receptor-level.

We recommend that this case be reported to the Regional Centre of the Swedish Adverse Drug Reactions Advisory Committee (SADRAC). 1 Swedis (The Swedish Drug Information System) 2 Upadhyaya HP, Devane CL: Lack of urinary side-effects with nefazodone as compared to other newer antidepressants. (Letter to the editor) Hum Psychopharmacol 1998; 13: 297-298 3 Benazzi F: Urinary retention with venlafaxine-fluoxetine combination. (Letter to the editor) Hum Psychopharmacol 1998; 13: 139-140 4 Mir S, Taylor D: The adverse effects of antidepressants. Curr Opin Psychiatry 1997; 10: 88-94