Acetaminophen

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  • Advise patient it is unsafe to take more than 4 grams of acetaminophen in a 24-hour period.
  • Instruct patient that many non-prescription combination products may contain acetaminophen.
  • Instruct patient to report signs/symptoms of gastrointestinal hemorrhage, hepatotoxicity, or nephrotoxicity.
  • Patient should take with a full glass of water.
  • Patient should not drink alcohol while taking this drug. Advise patients who drink more than 3 alcoholic drinks a day to consult a healthcare professional prior to taking acetaminophen.


Dosing - Adult
Dysmenorrhea: 650 to 1000 mg ORALLY every 4 h as needed, maximum 4 g/day
Dysmenorrhea: 650 mg RECTALLY every 4 to 6 h; maximum 6 suppositories/24 h
Fever: 650 to 1000 mg ORALLY every 4 h as needed, maximum 4 g/day
Fever: 650 mg RECTALLY every 4 to 6 h; maximum 6 suppositories/24 h
Headache: 650 to 1000 mg ORALLY every 4 h as needed, maximum 4 g/day
Headache: 650 mg RECTALLY every 4 to 6 h; maximum 6 suppositories/24 h
Pain (Mild to Moderate): 650 to 1000 mg ORALLY every 4 h as needed, maximum 4 g/day
Pain (Mild to Moderate): 650 mg RECTALLY every 4 to 6 h; maximum 6 suppositories/24 h


Dosing - Pediatric
Dysmenorrhea: 10 to 15 mg/kg/dose ORALLY every 4 to 6 h, maximum 5 doses/day
Dysmenorrhea: age 12 y and older, 650 mg ORALLY every 4 to 6 h, maximum 3.9 g/24 h
Dysmenorrhea: age 6 to 11 y, 325 mg ORALLY every 4 to 6 h, maximum 2.6 g/24 h
Fever: 10 to 15 mg/kg/dose ORALLY every 4 to 6 h, maximum 5 doses/day
Fever: age 6 to 12 y, 325 mg ORALLY every 4 to 6 h, maximum 2.6 g/24 h
Fever: age 3 to 6 y, 120 to 125 mg RECTALLY every 4 to 6 h; maximum 720 mg/24 h
Fever: age 1 to 3 y, 80 mg RECTALLY every 4 h
Fever: age 3 to 11 months, 80 mg RECTALLY every 6 h
Headache: 10 to 15 mg/kg/dose ORALLY every 4 to 6 h, maximum 5 doses/day
Headache: age 6 to 12 y, 325 mg ORALLY every 4 to 6 h, maximum 2.6 g/24 h
Headache: age 3 to 6 y, 120 to 125 mg RECTALLY every 4 to 6 h; maximum 720 mg/24 h
Headache: age 1 to 3 y, 80 mg RECTALLY every 4 h
Headache: age 3 to 11 months, 80 mg RECTALLY every 6 h
Pain (Mild to Moderate): 10 to 15 mg/kg/dose ORALLY every 4 to 6 h, maximum 5 doses/day
Pain (Mild to Moderate): age 6 to 12 y, 325 mg ORALLY every 4 to 6 h, maximum 2.6 g/24 h
Pain (Mild to Moderate): age 3 to 6 y, 120 to 125 mg RECTALLY every 4 to 6 h; maximum 720 mg/24 h
Pain (Mild to Moderate): age 1 to 3 y, 80 mg RECTALLY every 4 h
Pain (Mild to Moderate): age 3 to 11 months, 80 mg RECTALLY every 6 h

Warnings - Precautions
Acetaminophen-induced liver disease: pts who drink greater than 3 alcoholic drinks every day.

Adverse Effects - Common
Dermatologic: Rash
Adverse Effects - Serious
Gastrointestinal: Gastrointestinal hemorrhage
Hepatic: Hepatotoxicity
Renal: Nephrotoxicity
Respiratory: Pneumonitis
Mechanism of Action
Systemic: For acetaminophen:
Analgesic: The mechanism of analgesic action has not been fully determined. Acetaminophen may act predominantly by inhibiting prostaglandin synthesis in the central nervous system (CNS) and, to a lesser extent, through a peripheral action by blocking pain-impulse generation. The peripheral action may also be due to inhibition of prostaglandin synthesis or to inhibition of the synthesis or actions of other substances that sensitize pain receptors to mechanical or chemical stimulation.
Antipyretic: Acetaminophen probably produces antipyresis by acting centrally on the hypothalamic heat-regulating center to produce peripheral vasodilation resulting in increased blood flow through the skin, sweating, and heat loss. The central action probably involves inhibition of prostaglandin synthesis in the hypothalamus.
Antipyretic: Caffeine is a mild CNS stimulant. Caffeine-induced constriction of cerebral blood vessels, which leads to a decrease in cerebral blood flow and in the oxygen tension of the brain, may contribute to relief of some types of headache.
It has been suggested that the addition of caffeine to acetaminophen may provide a more rapid onset of action and/or enhanced pain relief with lower doses of the analgesic. However, the FDA has determined that studies performed to date have not demonstrated that caffeine is an effective analgesic adjuvant or that it does not interfere with acetaminophen"s efficacy as an antipyretic.

Mechanism of Action - Pharmacokinetics
Systemic: 1 to 4 h
Systemic: Approximately 90 to 95% of a dose is metabolized in the liver, primarily by conjugation with glucuronic acid, sulfuric acid, and cysteine. An intermediate metabolite, which may accumulate in overdosage after the primary metabolic pathways become saturated, is .
Systemic: Oral: Rapid; Rectal: varies
Systemic: Renal: 3% unchanged; Metabolites: primarily conjugates
Systemic: Hepatic: 90 to 95%

Clinical Effects - Treatment
ACETAMINOPHEN-ACUTE: Decontamination: Activated charcoal. Ipecac could interfere with NAC administration.
ACETAMINOPHEN-ACUTE: Acetylcysteine: N-ACETYLCYSTEINE (NAC): Administer if toxic plasma level, or toxic dose ingested and APAP level not readily available. ORAL NAC DOSE - 140 mg/kg load, 70 mg/kg Q 4 hrs for 72 hrs maintenance.
ACETAMINOPHEN-ACUTE: Intravenous infusion: 150 mg/kg NAC in 200 mL D5W over 60 min, followed by 50 mg/kg in 500 mL D5W over next 4 hrs, then 100 mg/kg in 1000 mL D5W over next 16 hrs. Standard intravenous dosing can cause hyponatremia and seizures secondary to large amounts of free water in young children; use of a NAC solution of 40 mg/mL is recommended.
ACETAMINOPHEN-ACUTE: Monitoring of patient: Obtain APAP level 4 hrs postingestion and plot on nomogram. Follow LFTs, renal function, PT or INR in patients with toxic APAP levels.
ACETAMINOPHEN-REPEATED SUPRATHERAPEUTIC: Decontamination: Generally NOT indicated. Consider activated charcoal if recent substantial dose.
ACETAMINOPHEN-REPEATED SUPRATHERAPEUTIC: Acetylcysteine: N-ACETYLCYSTEINE (NAC): Give if initial APAP serum level greater than 10 mcg/mL (greater than 66.16 S.I. Units (micromole/L)) or evidence of liver injury. NAC DOSE - Oral - 140 mg/kg load, 70 mg/kg Q 4 hrs maintenance; IV - 150 mg/kg in 200 ml D5W over 60 min, then 50 mg/kg in 500 ml D5W over 4 hr then 100 mg/kg in 1 L D5W over 16 hr. Standard intravenous dosing can cause hyponatremia and seizures secondary to large amounts of free water in young children; use of a NAC solution of 40 mg/mL is recommended.
ACETAMINOPHEN-REPEATED SUPRATHERAPEUTIC: Monitoring of patient: Obtain serum acetaminophen level, AST, ALT, and PT or INR.

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