Treatment Guidelines

Treatment guidelines for acetaminophen poisoning are based on the time to presentation to the ED after ingestion: acetaminophen ingestions less than 4 h prior to presentation, acetaminophen ingestions longer than 4 h but less than 24 h ago, and acetaminophen ingestions of unknown time or longer than 24 h prior to presentation (Fig 165:7). No further acetaminophen serum measurements are necessary once the need for NAC therapy has been determined. Treatment with NAC

should continue for the full 72-h course (18 doses).

FIG. 165-7. Treatment guidelines for acetaminophen ingestion. Abbreviations: ALT, alanine aminotransferase; APAP, ^-acetyl-p-aminophenol (acetaminophen); AST, aspartate aminotransferase; GI, gastrointestinal; LFTs, liver function tests; M/S ; NAC, ^-acetylcysteine; PT, prothrombin time; Rx, treatment.

For patients with acetaminophen ingestions who present within less than 4 h to the ED, treatment begins with GI decontamination (usually activated charcoal) and awaiting the determination of a 4-h postingestion acetaminophen level. If the hospital laboratory can determine the acetaminophen level within 8 h after ingestion, the clinician should wait for that measurement and plot it on the nomogram to determine whether NAC therapy is necessary. If the hospital laboratory cannot determine the acetaminophen level within 8 h, the clinician should empirically administer the first dose of NAC (within 8 h of acetaminophen ingestion) without waiting for the measurement. Subsequently, when the acetaminophen level is determined, it should be plotted on the nomogram to determine whether additional NAC therapy is necessary.

For patients with acetaminophen ingestions who present longer than 4 h but less than 24 h to the ED, the serum acetaminophen level should be determined by the laboratory as soon as possible. GI decontamination may be performed, but it may have limited effectiveness because of the delay in presentation. It should be considered more in light of possible coingestions. Similarly, if the hospital laboratory can determine the acetaminophen level within 8 h after ingestion, the clinician should wait for the serum acetaminophen level and plot it on the nomogram to determine whether NAC therapy is necessary. Otherwise, the first dose of NAC (within 8 h of acetaminophen ingestion, if possible) should be administered without waiting for the measurement. When the acetaminophen level is determined, it should be plotted on the nomogram to determine whether additional NAC therapy is necessary.

Finally, for acetaminophen ingestions of unknown time or longer than 24 h ago, the clinician should consider whether GI decontamination is required. A serum acetaminophen level should be determined and liver function tests (AST and ALT) should be performed by the hospital laboratory. In addition, the first dose of NAC therapy should be started as soon as possible. In this scenario, a detectable acetaminophen level (>10 pg/mL) suggests that the patient may be at risk for developing hepatotoxicity. Similarly, elevated AST and ALT enzymes suggest the possibility of ongoing hepatic toxicity. Therefore, continued NAC therapy is indicated if the acetaminophen level is measurable or if the serum AST or ALT is elevated.

Supportive therapy for acetaminophen poisoning, as in all overdose presentations to the ED, should include obtaining early IV access and a 12-lead electrocardiogram interpretation to exclude cardiac toxins (e.g., cyclic antidepressants, digoxin, b blockers, and calcium-channel blockers). Hypoglycemia and hypoxemia should be quickly considered and excluded for all patients presenting with altered sensorium. All patients requiring NAC therapy should be admitted to the hospital until the completion of the therapy. In general, admission to an unmonitored hospital bed is adequate unless a patient is hemodynamically unstable or a patient is suicidal and 24 h direct observation cannot be arranged. Patients who are not at risk for developing acetaminophen-induced hepatotoxicity (acetaminophen level below the nomogram, unmeasurable acetaminophen level with normal liver function test results) should be observed in the ED for a minimum of a 4 to 6-h period to exclude potentially toxic coingestants. This observation period is sufficient to exclude untoward events. Psychiatric evaluation should be considered for all patients with intentional acetaminophen overdose.

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