Acetaminophen: Action, Therapeutic effect, Uses, Administration, Side effects by nursesnote

 Acetaminophen 

Classification 

• Pharmacotherapeutic: central analgesic. 
• Clinical: Non-narcotic analgesic, antipyretic. 

Action 

Appears to inhibit prostaglandin synthesis in the CNS  and, to a lesser extent, block pain impulse through peripheral action. Acts centrally on hypothalamic heat-regulating center, producing peripheral vasodilation ( heat loss, skin erythema, diaphoresis).

Therapeutic effect: Results in antipyresis. Produces analgesic effect. 

Pharmacokinetics

Route: PO

Onset: less than 60 min

Peak: 1-3 hrs

Duration: 4-6 hrs

Rapidly, completely absorbed from GI tract; rectal absorption variable. Protein binding: 20%-50%. Widely distributed to most body tissues. Metabolized in liver; excreted in urine. 

Half-life: 1-4 hrs ( increased in those with hepatic disease, elderly, neonates; decreased in children ). 

Uses

Relief of mild to moderate pain, fever. 

IV: Management of moderate to severe pain when combined with opioid analgesia. 

Precautions 

Contraindications: Severe hepatic impairment or severe active liver disease. 

Caution: Sensitivity to acetaminophen; severe renal impairment; alcoholic hepatic disease, hepatic impairment, or active hepatic disease; chronic malnutrition and hypovolemia; limit dose to less than 4 gm/day. 

Lifespan considerations

Pregnancy/Lactation: Crosses placenta; distributed in breast milk. Routinely used in all stages of pregnancy,  appears safe for short-term use. 

Pregnancy category B

Children/Elderly: No age-related precautions noted. 

Interactions 

Drug: Alcohol, hepatotoxic medication ( e.g. phenytoin), hepatic enzyme inducers ( e.g. phenytoin, rifampin) may increase risk of hepatotoxicity with prolonged high dose or single toxic dose. May increase risk of bleeding with warfarin with chronic, high-dose use. 

Lab Values: May increase serum AST, ALT, bilirubin, prothrombin levels 

• Therapeutic serum level: 10-30 mcg/ml;
• Toxic serum level: greater than 200 mcg/ml. 

Administration/Handling 

IV: Does not require further dilution. Store at room temperature. Withdraw doses less than 1, 000 mg. 

Rate of administration: Infuse over 15 min. 

PO

Give without regard to meals. 

Rectal

Moisten suppository with cold water before inserting well up into rectum. Do not freeze suppositories. 

Indications/Routes/Dosage

Analgesia and antipyresis 

IV: Adults, Adolescents weighing 50 kg or more: 1,000 mg q6h or 650 mg q4h. Maximum single dose: 1,000 mg; Maximum total daily dose 4,000 mg. 

Adults, Adolescents weighing less than 50 kg: 15 mg/kg q6h or 12.5 mg/kg q4h. Maximum single dose 750 mg; Maximum total daily dose: 75 mg/kg/day ( 3, 750 mg). 

Children: 2-12 YRS: 15 mg/kg q6h or 12.5 mg/kg q4h. Maximum: 75 mg/kg/day, do not exceed 3,750 mg/day.

Infants and Children less than 2 years: 7.5 - 15 mg/kg q6h. Maximum: 60 mg/kg/day. 

Neonates: Loading dose: 20 mg/kg,  then 10 mg/kg q6 -12h. Maximum daily dose 22.5-40 mg/day depending on gestational age.

Side effects

Rare: hypersensitivity reaction. 

Adverse effects/toxic reaction 

Early signs of acetaminophen toxicity: Anorexia, nausea,  diaphoresis, fatigue within first 12-24 hrs.

Late sign of toxicity: Vomiting, right upper quadrant tenderness, elevated hepatic function tests within 48-72 hrs after ingestion. 

Antidote: Acetylcysteine