Can very high S-prolactin levels be caused by risperidone treatment?

Fråga: Can very high S-prolactin levels be caused by risperidone treatment? In a male patient, the S-prolactin was found to be 1245 mIU/L (ref 56-278 mIU/L).

Sammanfattning: The current patient´s prolactin levels may well be due to risperidone treatment. This side effect is often dose-dependent and prolactin levels may therefore decrease with a risperidone dose reduction. We recommend monitoring plasma concentrations of risperidone when changing dosage. An alternative would be to switch to an antipsychotic that is less likely to cause hyperprolactinaemia. However, patients should always be evaluated for other causes of hyperprolactinaemia if there are doubts to whether this is caused by drug treatment.

Svar: Hyperprolactinaemia is a common side effect of risperidone (1-3) and the Drug Information Centre has previously received several questions about this side effect. Among the cases in these previous questions, the prolactin levels of the patients have been up to 10 times higher than the reference value.

According to a review on S-prolactin levels in patients with schizophrenia or bipolar disorder, the increases are usually mild or moderate during treatment with antipsychotics, i.e., S-prolactin <2000 mIU/L (2,4). However, levels of up to 5000 mIU/L have been seen in this patient group. Endocrinological investigation is recommended at levels above 2500 mIU/L unless the patient is pregnant or breast-feeding, as these levels are usually caused by other factors than antipsychotic drugs (2). Please observe that Swedish laboratories changed their unit for serum prolactin levels from ug/L to mIU/L (conversion: 21.2 x ug/L= mIU/L) (5).

The temporal relationship between initiation of antipsychotic treatment and hyperprolactinaemia can support the diagnosis. However, this requires knowledge of the patient´s S-prolactin levels before treatment (2). According to some studies hyperprolactinaemia seems to be dose-dependent (2) and dose reduction may lower the S-prolactin levels. The risk of hyperprolactinaemia varies depending on that antipsychotic used, with the highest risk for risperidone (72-100% of treated patients) and amisulpride (up to 85%) (4). A possibility is to switch to a treatment with a lower risk of hyperprolactinaemia e.g. aripiprazole (up to 10%) or quetiapine (0-29%) (4).