CASE REPORT verapamil, arrhythmias Delayed Onset of Cardiac Arrhythmias From Sustained-Release Verapamil Sustained-release products in overdose are known to produce prolonged effects as well as delayed onset. The availability of sustained-release cal- cium channel blockers may produce an initial misleading picture for pa- tients who are at risk for serious toxicity. We report the cases of two adults who had delayed onset of arrhythmias after ingestion of sustained-release verapamil. In both cases, a single dose of activated charcoal was adminis- tered, but the patients still developed toxicity. Some of the unique prob- lems encountered with sustained-release formulations are discussed, and 24-hour cardiac monitoring for sustained-release calcium channel blocker overdoses, despite a possible early asymptomatic period, is suggested. [Spiller HA, Meyers A, Ziemba T, Riley M: Delayed onset of cardiac ar- rhythmias from sustained-release verapamil. Ann Emerg Med February 1991;20:201-203.] INTRODUCTION The introduction of sustained-release formulations of the calcium chan- nel antagonists brings new problems and risks in overdose not encountered in standard dosing formulations. Three calcium channel antagonists are available in the United States in sustained-release preparations: verapamil (Calan SR ® and Isoptin SR®), diltiazem (Cardizem SR®), and nifedipine (Procardia XL®). The popularity and ease of once-a-day dosing with sus- tained-release formulations are expected to advance their use with both patients and physicians. This growing availability increases the possibility of accidental and intentional exposure. We present two case reports of toxicity after intentional ingestion of a sustained-release verapamil preparation and briefly discuss some of the unique problems encountered with sustained-release formulations. CASE REPORTS Case One A 24-year-old man with a history of hypertension arrived in the emer- gency department approximately one hour after a witnessed ingestion of 11 240-mg verapamil tablets (total, 2.64 g). The patient was having an emo- tional dispute with his wife at the time of the overdose. He claimed he took 11 of the tablets because he thought they were aspirin. On arrival at the ED, he was in no acute distress, alert, and oriented times three and had a steady gait. Vital signs were blood pressure of 130/80 mm Hg; heart rate, 100 in a sinus rhythm; and respirations, 24. Auscultation of the lungs re- vealed clear breath sounds bilaterally. The abdomen was benign with ac- tive bowel sounds. The patient was lavaged with an orogastric tube, and no pill fragments were noted in the return. A single dose of 50 g of activated charcoal with sorbitol was administered. A 12-lead ECG was done two hours after inges- tion and compared with the patient's ECG from one month earlier; no changes were seen except for an increase in rate. A urine toxicologic screen revealed only cocaine metabolites. This drug screen specifically tests for ethanol, amphetamines, barbiturates, phencyclidine, cocaine, benzodiazepines, opiates, and cannabinoids. The patient was admitted to a monitored bed. Approximately seven to eight hours after ingestion, he developed first-degree atrioventricular Henry A Spiller, MS, RN* Amy Meyers, RPh* Thomas Ziemba, DOt Martina Riley, DO:~ Philadelphia, Pennsylvania From the Delaware Valley Regional Poison Control Center;* the Philadelphia College of Osteopathic Medicine;t and the Emergency Department, Nazareth Hospital,!: Philadelphia, Pennsylvania. Received for publication December 18, 1989. Revision received May 9, 1990. Accepted for publication June 4, 1990. Originally presented at the Annual Joint Scientific Meeting of The American Academy of Clinical Toxicology, American Association of Poison Control Centers, American Board of Medical Toxicology, and the Canadian Association of Poison Control Centers in Atlanta, Georgia, October 1989. Address for reprints: Henry A Spiller, MS, RN, Delaware Valley Regional Poison Control Center, One Children's Center, 34th and Civic Center Boulevard, Philadelphia, Pennsylvania 19104. 130/201 ,Annals of Emergency Medicine 20:2 February 1991