Perform an electrocardiogram (EKG) in all seriously ill patients in whom poisoning is being considered Detectable conduction delays (prolongation of the PR, QRS, and/or QT intervals) may provide diagnostic direction and impact management by predicting imminent life-threatening cardiac rhythm disturbances TABLE 102.7 FREQUENTLY USEFUL QUANTITATIVE TOXICOLOGY TESTS IN PEDIATRIC PATIENTS Drug/toxin Optimal time after ingestion (hours) Acetaminophen Carbamazepine Carboxyhemoglobin Digoxin Ethanol Ethylene glycol Iron Lithium Methanol Methemoglobin Phenobarbital Phenytoin Salicylate Theophylline Valproate 2–4 Immediate 4–6 ½–1 ½–1 2–4 a ½–1 Immediate 1–2 1–2 2–4 a 1–2 a 2–4 a Repeat levels over to 12 hours may be necessary with sustained-release preparations Adapted from Weisman RS, Howland MA, Flomenbaum NE The toxicology laboratory In: Goldfrank LR, Flomenbaum NE, Lewin NA, et al., eds Goldfrank’s Toxicologic Emergencies 4th ed Norwalk, CT: Appleton & Lange; 1990