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WESLEY R. ZEMRAK, PHARMD., is Pharmacy Practice Resident, Maine. Medical Center, Portland. GEORGE A. KENNA, PH.D., B.S.PHARM., is Assistant Professor of Psychiatry and Human Behavior (Research), Brown Medical School, Brown University, Providence, RI, and Clinical Pharmacist, The Westerly Hospital, Westerly, RI.

Address correspondence to Dr. Kenna at the Center for Alcohol and Addiction Studies, Box G-S121-5, Providence, RI 02903 (george_kenna{at}brown.edu).

Purpose. The association of antipsychotic and antidepressant drugs with Q-T interval prolongation is reviewed. Summary. Prolongation of the Q-T interval can be of particular concern to practitioners when prescribing antidepressants and antipsychotics. Patients may be at a greater risk for developing fatal arrhythmias when taking many of these drugs. In general, antipsychotics cause Q-T interval prolongation at a higher rate than do antidepressants. The typical antipsychotics thioridazine, pimozide, and intravenous haloperidol all have the highest potential for Q-T interval prolongation. The tricyclic antidepressants have a higher rate of Q-T interval prolongation than do selective serotonin-reuptake inhibitors (SSRIs), particularly at higher concentrations and in cases of overdose. In addition, nonpharmacologic risk factors such as existing heart disease, female sex, electrolyte abnormalities, hepatic insufficiency, and stimulant drug abuse contribute to the risk for developing these arrhythmias, as do pharmacologic factors such as multidrug therapy and high dosages of drugs known to prolong the Q-T interval. Risk factors may be identified in the patient’s history and demographic information. However, all pharmacists may not have this information readily available to them. Conclusion. Antipsychotics cause Q-Tc interval prolongation at a higher rate than do antidepressants, and the typical anti-psychotics thioridazine, pimozide, and i.v. haloperidol all have the highest potential for Q-Tc interval prolongation. Tricyclic antidepressants have a higher rate of Q-Tc interval prolongation than do the SSRIs, particularly at higher concentrations and in overdose situations. The frequency of adverse events associated with drug-induced Q-T interval prolongation is unknown. Index terms: Antidepressants; Antipsychotic agents; Dosage; Haloperidol; Long QT syndrome; Pimozide; Thioridazine; Toxicity