• Yusuke Iwata, Shinichiro Nakajima, Fernando Caravaggio, Takefumi Suzuki, Hiroyuki Uchida, Eric Plitman, Jun Ku Chung, Wanna Mar, Philip Gerretsen, Bruce G Pollock, Benoit H Mulsant, Tarek K Rajji, David C Mamo, and Ariel Graff-Guerrero.
• Multimodal Imaging Group, Research Imaging Centre, Centre for Addiction and Mental Health, Toronto, Canada.
• J Clin Psychiatry. 2016 Dec 1; 77 (12): e1557-e1563.

ObjectiveAlthough hyperprolactinemia carries a long-term risk of morbidity, the threshold of dopamine D2/3 receptor (D2/3R) occupancy for hyperprolactinemia has not been investigated in older patients with schizophrenia. Data were taken from a positron emission tomography (PET) study conducted between August 2007 and August 2015. The present post hoc study included 42 clinically stable outpatients with schizophrenia (DSM-IV) (mean ± SD age = 60.2 ± 6.7 years) taking olanzapine or risperidone. Subjects underwent [¹¹C]-raclopride PET scans to measure D2/3R occupancy before and after reducing their dose of antipsychotic by up to 40%. Blood samples were collected before each PET scan to measure prolactin levels.MethodsThe relationship between prolactin levels and D2/3R occupancy was examined using stepwise linear regression analyses. The D2/3R occupancy thresholds for hyperprolactinemia were explored using Fisher exact tests.ResultsProlactin levels decreased following dose reduction (mean ± SD = 24.1 ± 30.2 ng/mL to 17.2 ± 15.1 ng/mL; P < .001). Prolactin levels were associated with female gender (β = .32, P = .006, vs male), antipsychotics (β = .23, P = .02, risperidone vs olanzapine), and D2/3R occupancy (β = .23, P = .04). Those with D2/3R occupancy of 66% or higher were more likely to have hyperprolactinemia than those with D2/3R occupancy lower than 66% (P = .03). Sensitivity, specificity, positive predictive value, and negative predictive value of this threshold were 0.44, 0.81, 0.78, and 0.48, respectively. We identified a D2/3R occupancy threshold for hyperprolactinemia of 66% in older patients with schizophrenia, which is lower than that reported in younger patients (73%) by other researchers.ConclusionsOur results suggest a higher sensitivity to antipsychotics in older patients. Prolactin levels could assist in the determination of appropriate antipsychotic dosing to minimize adverse effects.Trial RegistrationClinicalTrials.gov identifier: NCT00716755.© Copyright 2016 Physicians Postgraduate Press, Inc.

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