Urinary retention caused after fluoxetine–risperidone combination

Abstract

A case of urinary retention emerging after fluoxetine (20 mg/day) addition to low risperidone doses (2 mg/day) is presented. Severe extrapyramidal side-effects (EPS) also occurred after fluoxetine–risperidone combination. Several possibilities, based on the pharmacodynamic and pharmacokinetic properties of risperidone and fluoxetine, which merit consideration in an attempt to explain our patient's side-effects, are discussed. Extrapyramidal side-effects can be due to an increase of the plasma concentration of risperidone and/or the intrinsic propensity of fluoxetine to produce EPS. Urinary retention may be the consequence of a central serotoninergic mechanism in, or without, combination central D2 blockade.