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Acetaminophen is the most widely used analgesic and a commonly used antipyretic. It has been available as an over-the-counter formulation for more than 40 years and is exceptionally safe when used according to manufacturer directions. Unfortunately, toxic levels can make it a silent and lethal killer, as overdose may initially present with few, if any, symptoms.13 If not promptly discovered and treated, acetaminophen toxicity can lead to liver failure and death (unless a successful liver transplant is performed).410

Acetaminophen is packaged under multiple names and is a component of many different medicinal products around the globe. In the United States it is commonly sold as the brand name Tylenol®, while in the United Kingdom it is generally sold under the alternate generic names of paracetamol and N-acetyl-p-aminophenol (APAP).11

In the United States, acetaminophen is available in varied doses and forms. Pill forms are made in 325- and 500-mg immediate release, as well as 650-mg extended release. For both products, the adult dose should not exceed 4 g per day.12 Pediatric formulas vary in both dosing and form, including concentrated drops, liquid suspensions, suppositories, and dissolving or chewable tablets.11,12 Pediatric doses (child and infant) should not exceed 90 mg/kg per day or 15 mg/kg per dose every 4 hours.11

Acetaminophen is found in many over-the-counter and prescription medicines (i.e., Sudafed PE® Severe Cold: acetaminophen, diphenhydramine, and phenylephrine; Percocet®: acetaminophen and oxycodone; Fioricet®: acetaminophen, butalbital, and caffeine). Unintentional overdose may occur with these multidrug products, as the general public is unaware of the multiple names.

Acetaminophen overdose may be acute or chronic (Figure 42-1). An acute overdose is generally defined as a toxic dose (>150 mg/kg) ingested in less than 8 hours. A chronic overdose is generally defined as a toxic dose taken over more than 8 hours. Overdose may be accidental, as is frequently the case with pediatric overdoses, or it may also be intentional, as is the case with suicide attempt.

Figure 42-1.

Acute versus chronic overdose.

Overdose is defined as anything over the recommended 4 g per day. However, for the average adult (70 kg), the acetaminophen ingestion necessary for hepatotoxicity is much higher—150 mg/kg, or approximately 10.5 g. Thus, approximately 20 extra strength (500 mg each) pills are potentially lethal for the average patient.1,13 Since acetaminophen is readily available over-the-counter, it is an easy overdose agent for suicide attempts.

Additionally, pediatric dosing (child and infant formulas) is easy to confuse and can often lead to therapeutic error. Pediatric dosing is particularly problematic since the infant's formula (100 mg/mL) is more than three times as concentrated when compared with the children's formula (32 mg/mL).11 Thus, equal ...

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