Toxicity can occur following acute ingestion or develop during chronic therapy (Table 108-1). Acute toxicity typically presents with nausea, vomiting, or abdominal pain. Characteristic cardiac effects include bradyarrhythmias and/or supraventricular tachycardia with atrioventricular block. Severe toxicity can result in ventricular arrhythmias. Chronic toxicity is more common in the elderly and often occurs as a result of concomitant illness (heart disease, renal/liver failure, hypothyroidism, chronic obstructive pulmonary disease), electrolyte abnormality (hypokalemia, hypomagnesemia), or drug interactions (quinidine, amiodarone, spironolactone, calcium channel blockers, macrolide antibiotics). Neuropsychiatric symptoms are more common with chronic toxicity, though cardiac effects are similar to those seen with acute toxicity.