Hyperprolactinemia is a frequent consequence of treatment with antipsychotic agents, partially because the prolactin response to antipsychotics is related to dopamine blockade. Recent studies have suggested that the prolactin response to olanzapine is weaker than that to risperidone. Thus, we studied the effects of various factors on the elevated plasma prolactin levels caused by these medications. The subjects were 94 patients with acutely exacerbated schizophrenia (46 males, 48 females). For four weeks, they received 6mg of risperidone and 20mg of olanzapine daily. Plasma samples were collected before the medications were given and 12h after the bedtime dosing each week. Treatment with either risperidone or olanzapine boosted plasma prolactin levels above baseline in both males and females. Prolactin levels were significantly higher in females than in males at all sampling points in both treatments. Risperidone increased prolactin significantly more than did olanzapine in both males and females. Delta prolactin (prolactin level at four weeks minus the baseline prolactin level) during olanzapine treatment significantly correlated with olanzapine concentration at 4th week (r=-0.518, p<0.01) only in males. Multiple regression analyses showed that delta prolactin during risperidone was significantly correlated with gender (p<0.001) and age (p<0.05) and that delta prolactin during olanzapine significantly correlated with gender (p<0.001) and drug concentration (p<0.01). The present study suggests that the predominant factors influencing hyperprolactinemia are young female for risperidone treatment, and being female and lower drug concentration as a predictor for hyperprolactinemia under olanzapine.
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