The interesting letter by Kapur et al raises a number of issues that I have been intimately involved with for nearly a decade, issues on which our views sometimes differ significantly. I have proposed that atypical antipsychotic drugs such as clozapine, risperidone, and olanzapine are appropriately defined as antipsychotics with low extrapyramidal symptoms (low EPS) at average clinical doses, and that attempts to expand this definition to include additional actions that only some of these drugs have, such as a greater ability to improve negative symptoms, are ill advised.1 In fact, the historic definition of an atypical antipsychotic agent included low EPS at clinically effective antipsychotic doses. There is not yet evidence for any other single property shared by all of the new atypical drugs, including the ability to improve negative symptoms to a greater extent than typical neuroleptic drugs. Other differences have emerged with regard to cognitive function and prolactin secretion as well as efficacy in patients who are resistant to treatment.
Meltzer H. Do Loxapine Plus Cyproheptadine Make an Atypical Antipsychotic? PET Analysis of Their Dopamine D2 and Serotonin2 Receptor Occupancy. Arch Gen Psychiatry. 1998;55(7):667-668. doi: