Daytime variations in serum prolactin levels in patients receiving oral and depot antipsychotic medication

Serum prolactin levels in psychiatric inpatients were measured at 8:00 AM prior to administration of oral chlorpromazine (CPZ) at 9:00 AM, and at hourly intervals throughout the day until 3:00 PM. Sixteen patients receiving CPZ 400 mg in equally divided doses of 200 mg twice daily at 9:00 AM and 9:00 PM and six patients who had received fluphenazine decanoate (FD) in doses of 25 to 75 mg 2 to 3 weeks prior to study were evaluated. In patients receiving oral CPZ, serum prolactin levels were elevated in the 8:00 AM samples; serum prolactin levels decreased between 8:00 AM and 10:00 AM and then increased sharply, reaching their peak from 11:00 AM to 2:00 PM. Serum prolactin levels were moderately elevated but relatively stable throughout the day in patients who had received im FD. The 8:00 AM serum prolactin levels were correlated with the peak serum prolactin levels during the day in female patients receiving oral CPZ, but not in male patients. The lack of correlation between base line and peak serum prolactin levels in male patients is most likely due to interference from the sleep-induced prolactin increase in 8:00 AM samples. Serum prolactin levels at 9:00 AM were significantly correlated with peak serum prolactin levels in both male and female patients. The importance of determining diurnal variation in serum prolactin levels in psychiatric patients is discussed.