We were pleased by Drs Waddington and Molloy's positive response to our study of tardive dyskinesia (TD)1 and encouraged by their similar findings in animals. We agree with their general conclusion that clinical investigations and studies using animal models have their greatest potential utility when designed to address complementary issues. But we remain cautious about generalizing— either to other human age groups or to other species—our clinical finding in aged psychiatric patients of a fairly brief "threshold" of neuroleptic exposure apparently associated with producing a period of maximum risk for the occurrence of TD. There are several general but related sources of our caution, the first of which is not addressed by Drs Waddington and Molloy and is problematic both in clinical investigations and in animal studies.The potential TD risk factors of subject age and duration of neuroleptic exposure are necessarily closely related and difficult to
Toenniessen LM, McFarland BH, Casey DE. Duration of Treatment Relationships for Involuntary Movements (Tardive Dyskinesia): Concordance Between Cross-sectional, Clinical, and Longitudinal Animal Studies?-Reply. Arch Gen Psychiatry. 1986;43(2):191–192. doi:10.1001/archpsyc.1986.01800020101019
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