Reply to "Intrinsic Activity of Aripiprazole Is Not 30% of Dopamine, But Only About 6% Under Ideal Antipsychotic Therapy"

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Letter to the Editor

Sir: I appreciate the letter from Drs. Hamamura, Kodama, and Harada but must respectfully disagree with their argument as follows:
Dr. Hamamura and colleagues suggest that the intrinsic activity of a partial receptor agonist is derived mathematically from the percentage of the target receptor occupied by different doses of the partial agonist versus the percentage of that receptor occupied by its endogenous agonist under normal physiologic conditions. Instead, the intrinsic activity of a partial agonist is determined by measuring its maximal functional effect on its target receptor versus the maximal functional effect of the endogenous agonist of the same receptor. Admittedly, there should be some agreement between these 2 different concepts since the latter is a major determinant of the former.

J Clin Psychiatry 2008;69(5):864-865