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Effects of Age and Age of Onset on Prescribed Antipsychotic Dose in Schizophrenia Spectrum Disorders: A Survey of 1,418 Patients in Japan

From the Department of Neuropsychiatry, Keio University, School of Medicine, Tokyo (HU, TS, KW, GY, MT); Centre for Addiction and Mental Health, Toronto, ON, Canada (HU, DCM, BHM); Department of Psychiatry, University of Toronto, Toronto, ON, Canada; Department of Psychiatry, Inokashira Hospital, Tokyo (TS); Department of Psychiatry, National Defense Medical College, Saitama, Japan (AT); Graduate School of Health Management, Keio University, Kanagawa, Japan (AI); Department of Psychiatry, Ohizumi Hospital, Tokyo (KW); Suisei Healing Center, Kanagawa, Japan (GY); and Asakadai Mental Clinic, Saitama, Japan (MT).

Objectives: The relationship between age and prescribed antipsychotic dose in patients with schizophrenia has been examined by assuming only a linear correlation in two age subgroups at most. The age of illness onset has also not been under adequate consideration in past prescription surveys. The objective of this study was to better evaluate these age effects on antipsychotic dose prescribed in these patients across a broad age range.

Methods: Review of prescriptions for antipsychotic medications in patients with schizophrenia spectrum disorders was conducted across 30 sites in Tokyo. A total of 1,418 patients (655 inpatients, 763 males, age range: 16.6–90.2 years) were studied.

Results: Age had significant effects on prescribed antipsychotic dose; the dose increased with age through the third decade, subsequently plateaued, and decreased after the fifth decade. The age of illness onset also had significant effects on the dose; late-onset schizophrenia (LOS) and very-late-onset schizophrenia-like psychoses (VLOS) patients received lower doses than early onset schizophrenia (EOS) patients. LOS and VLOS patients who did not experience any hospitalization for the previous year were treated with and , respectively, of the dose for EOS of comparable current age.

Conclusion: Our results suggested biphasic effects of age on antipsychotic dose prescribed in patients with schizophrenia spectrum disorders. The natural history of schizophrenia and physiological aging may contribute to this inverted U-shaped relationship. In addition, our results may add another evidence of distinction among EOS, LOS, and VLOS from a clinical psychopharmacological perspective.