1. Introduction
Acetaminophen, also known as paracetamol, is a widely used analgesic (pain reliever) and antipyretic (fever reducer). It works by inhibiting prostaglandin synthesis in the central nervous system (CNS) and has minimal anti-inflammatory effects compared to NSAIDs.
2. Indications
- Mild to moderate pain (e.g., headaches, muscle pain, dental pain, arthritis pain)
- Fever (antipyretic use)
- Postoperative pain relief
- Pain relief in patients who cannot take NSAIDs (e.g., those with gastric ulcers, kidney disease, or aspirin allergy)
3. Dosage
Adults & Adolescents (≥12 years):
- Oral: 500–1,000 mg every 4–6 hours as needed
- Max daily dose: 4,000 mg (4 g/day)
- Chronic use (for long-term pain relief): Max 3,000 mg/day
Paediatric Use (≤12 years):
- Oral Suspension: 10–15 mg/kg per dose every 4–6 hours
- Max dose: 75 mg/kg/day
Elderly (>65 years):
- Max dose: 3,000 mg/day due to reduced liver function.
Renal Impairment:
- CrCl <30 mL/min: Dosing interval should be every 6–8 hours instead of 4–6 hours.
Hepatic Impairment:
- Use with caution; reduce dose to a max of 2,000 mg/day in patients with chronic liver disease or alcoholism.
4. Administration
- Take with or without food (but taking with food may slow absorption).
- Do not exceed the recommended daily dose to avoid liver toxicity.
- Oral liquid forms should be measured with a proper dosing device (not a household spoon).
5. Forms Available
- Tablets: 325 mg, 500 mg, 650 mg
- Caplets: 500 mg, 650 mg
- Oral Suspension/Syrup: 120 mg/5 mL, 160 mg/5 mL
- Effervescent Tablets: 500 mg
- Suppositories: 80 mg, 120 mg, 325 mg, 650 mg
- IV Injection (Paracetamol IV): 1,000 mg/100 mL
6. Side Effects
6.1 Common Side Effects:
- Nausea
- Rash (rare)
- Headache
6.2 Less Common Side Effects:
- Mild drowsiness
- Stomach upset (rare)
6.3 Rare but Serious Side Effects:
- Liver toxicity (hepatotoxicity) (most serious risk, especially at high doses)
- Severe skin reactions (e.g., Stevens-Johnson Syndrome, Toxic Epidermal Necrolysis – very rare)
- Kidney damage (if used in very high doses long-term)
7. Warnings
- Liver Toxicity (Hepatotoxicity):
- Exceeding 4,000 mg/day can cause acute liver failure.
- Alcohol consumption significantly increases liver toxicity risk—limit or avoid alcohol.
- Severe Skin Reactions:
- Rare but serious skin conditions like Stevens-Johnson Syndrome (SJS)—stop use if rash develops.
- Overdose Risk:
- Symptoms include nausea, vomiting, abdominal pain, confusion, liver failure.
- Antidote: N-acetylcysteine (NAC) is the treatment for acetaminophen overdose.
8. Precautions
- Avoid chronic high doses in patients with liver disease or alcoholism.
- Safe in most patients with gastric ulcers or bleeding risk (unlike NSAIDs).
- Use with caution in patients with severe malnutrition—increased risk of hepatotoxicity.
9. Interactions
- Alcohol: Increased risk of liver toxicity.
- Warfarin: Increased risk of bleeding (monitor INR if using long-term).
- Rifampin, Phenytoin, Carbamazepine: May increase liver metabolism of acetaminophen, reducing effectiveness and increasing toxicity risk.
- Chronic NSAID Use (e.g., ibuprofen, aspirin): May increase risk of kidney damage.
10. Monitoring Parameters
- Liver function tests (ALT, AST) if used chronically.
- INR levels in patients on warfarin.
- Kidney function (eGFR, creatinine) if used long-term at high doses.
11. Use in Children
- Safe and widely used for fever and pain relief in infants and children.
- Use weight-based dosing for accuracy.
12. Use in Pregnancy
- Category B:
- Safe in pregnancy at recommended doses (often preferred over NSAIDs).
- May be linked to ADHD risk in long-term use during pregnancy (still debated).
13. Use in Elderly
- Generally safe, but limit to 3,000 mg/day due to reduced liver metabolism.
14. Use in Kidney Disease
- Mild impairment: No dose adjustment.
- Severe impairment (CrCl <30 mL/min): Increase dosing interval to every 6–8 hours.
15. Use in Liver Disease
- Max dose: 2,000 mg/day in patients with chronic liver disease or alcoholism.
16. Patient Counselling Points
- Do not exceed 4,000 mg per day (or 3,000 mg for long-term use).
- Check OTC medication labels—many contain acetaminophen (e.g., cold and flu medicines).
- Avoid alcohol while taking acetaminophen to prevent liver damage.
- Seek medical help if overdose is suspected (even if no symptoms at first).
- Use the correct measuring device for liquid formulations in children.
17. Table of Brand Names, Manufacturer, and Prices in USD
Brand Name | Manufacturer | Strength/Dosage Form | Price (USD) |
---|---|---|---|
Tylenol | Johnson & Johnson | 325 mg, 500 mg Tablets | $8 (100 tabs) |
Panadol | GlaxoSmithKline | 500 mg Tablets | $6 (100 tabs) |
Paracetamol IV | Various | 1,000 mg/100 mL IV | $30 (1 vial) |
Generic Acetaminophen | Various | 325 mg, 500 mg, 650 mg Tablets | $5 (100 tabs) |
18. 15 FAQs (Frequently Asked Questions)
1. What is Acetaminophen used for?
It is used for pain relief and fever reduction.
2. How does Acetaminophen work?
It inhibits prostaglandin synthesis in the CNS, reducing pain and fever.
3. Can I take Acetaminophen on an empty stomach?
Yes, it does not irritate the stomach like NSAIDs.
4. Does Acetaminophen cause drowsiness?
No, it does not cause drowsiness.
5. Can I take Acetaminophen with ibuprofen?
Yes, they work differently and can be alternated for better pain relief.
6. Can Acetaminophen cause liver damage?
Yes, at high doses (>4,000 mg/day) or with alcohol use.
7. Is Acetaminophen safe for pregnancy?
Yes, it is safe in pregnancy when used at recommended doses.
8. How long does it take for Acetaminophen to work?
15–30 minutes, with full effect in 1 hour.
9. Can I take Acetaminophen with antibiotics?
Yes, there are no major interactions with antibiotics.
10. Can Acetaminophen cause kidney damage?
Rarely, but long-term high-dose use can affect kidney function.