Side Effects of Ziprasidone
Ms. A was a 52-year-old woman with a lifelong history of severe mood disorder not otherwise specified and borderline personality syndrome. At age 48, she developed a small right cerebrovascular accident secondary to toxic shock syndrome. She had potassium wasting secondary to diuretic treatment, which necessitated her taking exogenous potassium in the form of sustained-release potassium chloride. In addition, she suffered from mild emphysema due to cigarette smoking. For her psychiatric disorders, Ms. A received a medication cocktail consisting of fluoxetine, lamotrigine, amitriptyline, and clonazepam, which brought her significant emotional relief. Of all of the medications Ms. A received, only amitriptyline had potentially destabilizing effects on her myocardium. Nevertheless, she had long used this drug at stable therapeutic levels and obtained multiple serial ECGs without any prior signs of deleterious effects.Three months before her crisis, Ms. A had received a trial of ziprasidone up to 160 mg/day without ill effect. She then discontinued the drug because of its lack of efficacy in controlling her mood instability and did not receive replacement treatment with another antipsychotic. She did not experience ill effects of any sort during the trial period or during the reduction phase. Her other medications remained unchanged.About a month after discontinuing ziprasidone, Ms. A inadvertently discontinued her potassium chloride. Soon after, she became confused and ataxic. As a result of her confusion, she began to self-administer ziprasidone in the previous dose for an indeterminate period. A few days before hospital admission, she visited her internist, who, despite her complaints, found her neurologically intact. He ordered magnetic resonance imaging, which showed no change from an earlier reading. He did not perform an ECG or order measures of her electrolyte levels.Later, after becoming stuporous and repeatedly falling, Ms. A went to an emergency room and was promptly admitted to an intensive care unit because of her abnormal ECG. The ECG showed a markedly lengthened QTc interval, varying from 680 to 720 msec. Her ventricular rate was 75 bpm. Her P-R interval was 166 msec, and her QRS interval was 92. Her cardiac axes were shifted slightly to the right, in keeping with previous readings. Her heart remained in normal sinus rhythm. Her initial potassium level was 1.8 mEq/liter, and her magnesium level was 2.4 mEq/liter. Her potassium oxide level was 74.0 mEq/liter, and her pH was 7.48. Once she received intravenous potassium and magnesium, her QTc interval slowly returned to normal, in close conjunction with improving levels of the two electrolytes.
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