Urinary retention caused after fluoxetine-risperidone combination

A case of urinary retention emerging after fluoxetine (20 mg/day) addition to low risperidone doses (2 mg/day) is presented. Severe extrapyramidal sid e-effects (EPS) also occurred after fluoxetine-risperidone combination. Sev eral possibilities, based on the pharmacodynamic and pharmacokinetic proper ties 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 risperidon e and/or the intrinsic propensity of fluoxetine to produce EPS. Urinary ret ention may be the consequence of a central serotoninergic mechanism in, or without, combination central D-2 blockade.