Dose, mode of action, indication, contraindication, side effects of paracetamol
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Paracetamol (Acetaminophen)
Class: Non-opioid analgesic and antipyretic. It has little anti-inflammatory activity and does not cause the usual NSAID-related gastric irritation or platelet inhibition.
Dose
| Group | Usual dose | Maximum |
|---|---|---|
| Adults and adolescents ≥50 kg | 500-1000 mg orally every 4-6 hours as needed | 4000 mg/day from all products combined |
| Adults with risk of liver toxicity such as chronic alcohol use, malnutrition, low body weight, or liver disease | Use the lowest effective dose. Many clinicians limit to 2000-3000 mg/day | Follow prescriber/local guidance |
| Children | 10-15 mg/kg/dose orally every 4-6 hours | Do not exceed 5 doses in 24 hours. Use the specific product label or pediatric advice for the daily maximum |
| IV acetaminophen | Weight-based dosing and administration by trained clinicians | Product-specific limits apply |
Check combination cold, flu, and opioid medicines for paracetamol/acetaminophen to avoid accidental overdose. The labeled adult maximum is 4 g/day; exceeding this can cause severe or fatal liver injury. FDA prescribing information
Mode of action
- Acts mainly in the central nervous system.
- Reduces central prostaglandin synthesis, probably through inhibition of central cyclooxygenase-related pathways.
- Raises the hypothalamic temperature-regulating set point, producing an antipyretic effect.
- Produces analgesia through central pain-modulating pathways.
- It has minimal peripheral cyclooxygenase inhibition, so it has weak anti-inflammatory action, does not significantly impair platelet aggregation, and has less gastrointestinal toxicity than NSAIDs.
Indications
- Mild to moderate pain: headache, toothache, musculoskeletal pain, postoperative pain, dysmenorrhea.
- Fever.
- An alternative analgesic/antipyretic when NSAIDs are unsuitable, for example in people at risk of peptic ulcer disease or bleeding.
- Often combined with an opioid for moderate to severe acute pain.
Contraindications
Do not use in:
- Known hypersensitivity to paracetamol/acetaminophen or formulation ingredients.
- Severe hepatic impairment or severe active liver disease.
The US injectable product label specifies both as contraindications. DailyMed label
Use with particular caution or only under medical advice in:
- Chronic liver disease or hepatitis.
- Regular heavy alcohol intake.
- Malnutrition, prolonged fasting, dehydration, or very low body weight.
- Severe renal impairment, especially with repeated use.
- Concurrent use of other paracetamol-containing products.
- Long-term warfarin treatment, because regular high-dose use can increase INR.
Side effects
At therapeutic doses, paracetamol is usually well tolerated.
Common or mild
- Nausea, vomiting.
- Headache.
- Rash or itching, uncommon.
Uncommon but serious
- Hepatotoxicity and acute liver failure, especially after overdose, repeated excessive dosing, alcohol use, fasting, or use of multiple combination products.
- Hypersensitivity reactions: urticaria, angioedema, bronchospasm, or anaphylaxis.
- Rare severe skin reactions: Stevens-Johnson syndrome, toxic epidermal necrolysis, and acute generalized exanthematous pustulosis.
- Rare blood dyscrasias such as thrombocytopenia.
- Renal injury is uncommon at normal doses but may occur with chronic excessive use or overdose.
Key safety point: urgent medical assessment is needed after a suspected overdose even if the person feels well, because liver injury may initially be symptom-free.
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