Home Drug Guide Acetaminophen

Drug Guide

Generic Name

Acetaminophen

Brand Names Neopap, Tylenol, Injectapap, Acephen, Infants' Feverall, Ofirmev

Classification

Therapeutic: Analgesic, Antipyretic

Pharmacological: Cyclooxygenase (COX) inhibitor (central action)

FDA Approved Indications

Relief of mild to moderate pain
Reduction of fever

Mechanism of Action

Acetaminophen exerts its analgesic and antipyretic effects primarily through central inhibition of COX enzymes in the brain, which reduces prostaglandin synthesis involved in pain and fever regulation.

Dosage and Administration

Adult: Regular strength: 325-1000 mg every 4-6 hours as needed, not to exceed 4 grams per day. Extended-release formulations vary; always follow package instructions.

Pediatric: Based on weight, typically 10-15 mg/kg/dose every 4-6 hours as needed. Max dose depends on weight and age, generally not exceeding 75 mg/kg/day.

Geriatric: Similar to adult dosing; assess renal and hepatic function, adjust if necessary.

Renal Impairment: Adjust dose; use with caution, monitoring hepatic function.

Hepatic Impairment: Use with caution; dose reduction may be necessary, especially in chronic use.

Pharmacokinetics

Absorption: Rapidly absorbed from gastrointestinal tract.

Distribution: Widely distributed, crosses blood-brain barrier.

Metabolism: Primarily hepatic via conjugation to inactive glucuronide and sulfate metabolites; minor pathway involves CYP enzymes to a toxic metabolite (NAPQI).

Excretion: Renally excreted as conjugates.

Half Life: Approximately 2-3 hours in healthy adults.

Contraindications

Known hypersensitivity to acetaminophen.
Severe hepatic impairment.

Precautions

Use with caution in patients with hepatic disease or alcoholism.
Monitor hepatic enzymes in prolonged therapy.
Avoid concomitant use with other hepatotoxic drugs or alcohol.

Adverse Reactions - Common

Hepatotoxicity (Rare but serious, dose-related)
Rash (Uncommon)
Other hypersensitivity reactions (e.g., angioedema, anaphylaxis) (Rare)

Adverse Reactions - Serious

Acute liver failure (Rare, but potentially fatal)
Anaphylaxis (Rare)

Drug-Drug Interactions

Alcohol (increases hepatotoxicity risk)
Warfarin (may enhance anticoagulant effect)

Drug-Food Interactions

N/A

Drug-Herb Interactions

N/A

Nursing Implications

Assessment: Monitor pain severity, temperature, baseline hepatic function.

Diagnoses:

Risk for hepatotoxicity
Ineffective pain management

Implementation: Administer with food or water if gastrointestinal upset occurs. Monitor hepatic enzymes during prolonged therapy.

Evaluation: Assess pain relief, reduction in fever, and absence of adverse effects.

Patient/Family Teaching

Do not exceed recommended dose.
Avoid alcohol consumption.
Notify healthcare provider if symptoms of liver damage occur (e.g., jaundice, dark urine).
Use properly measured dosing devices.

Special Considerations

Black Box Warnings:

Severe hepatotoxicity risk with overdose or chronic use.
Risk increases with alcohol use.

Genetic Factors: Genetic polymorphisms may influence metabolism, but routine testing is not standard.

Lab Test Interference: May interfere with certain blood tests, such as liver function tests.

Overdose Management

Signs/Symptoms: Nausea, vomiting, jaundice, confusion, hepatotoxicity signs.

Treatment: (Administer antidote) N-acetylcysteine ideally within 8-10 hours of overdose to prevent liver damage.

Storage and Handling

Storage: Store at room temperature, away from moisture and heat.

Stability: Stable when stored properly.