Paracetamol (Acetaminophen) 650mg is a widely used, centrally-acting, non-opioid analgesic and antipyretic agent. It is a first-line treatment for mild to moderate pain and fever. Unlike NSAIDs, it has minimal anti-inflammatory activity and a favorable gastrointestinal safety profile. In the Indian context, it is one of the most commonly consumed over-the-counter (OTC) and prescribed medicines, available in numerous single and combination formulations.
Adult: 650mg every 4-6 hours as needed for pain or fever. Do not exceed 4 grams (4000mg) in 24 hours. A lower maximum of 3 grams (3000mg) per day is recommended for long-term use, in the elderly, or in those with risk factors for hepatotoxicity.
Note: May be taken with or without food. Taking with food may slightly delay absorption. Swallow tablet whole with a full glass of water. Do not crush, chew, or break extended-release formulations. For rapid relief, take on an empty stomach. Do not use for more than 3 days for fever or 5 days for pain without consulting a doctor.
The exact mechanism is not fully elucidated but is distinct from NSAIDs. It acts primarily centrally by inhibiting prostaglandin synthesis in the central nervous system (CNS). It is a weak inhibitor of peripheral cyclooxygenase (COX) enzymes, particularly COX-2, with minimal effect on COX-1, explaining its lack of significant anti-inflammatory or antiplatelet activity and its low gastrointestinal toxicity.
Pregnancy: Pregnancy Category A (Australian categorization) / Category B (US FDA). Considered safe for short-term use in all trimesters for pain and fever. Crosses the placenta. Avoid long-term/high-dose use. Preferred over NSAIDs, especially in third trimester.
Driving: No known effects on driving ability. However, if pain or fever is severe enough to impair alertness, driving should be avoided.
| Warfarin | Chronic high-dose paracetamol (>2g/day for several days) may potentiate anticoagulant effect, increasing INR and risk of bleeding. | Major |
| Isoniazid | Increases the formation of the toxic metabolite NAPQI via CYP2E1 induction, significantly raising risk of hepatotoxicity, even at therapeutic doses. | Major |
| Carbamazepine, Phenytoin, Phenobarbital | Enzyme inducers increase NAPQI formation, increasing hepatotoxicity risk. Dose reduction of paracetamol may be needed. | Moderate |
| Alcohol (Chronic, heavy use) | Induces CYP2E1 and depletes glutathione, dramatically increasing risk of severe and potentially fatal hepatotoxicity with therapeutic or supratherapeutic doses. | Major |
| Probenecid | May decrease the metabolic clearance of paracetamol, leading to increased plasma levels. Dose reduction may be necessary. | Moderate |
| Metoclopramide, Domperidone | May increase the absorption rate of paracetamol. | Minor |
| Cholestyramine | Reduces absorption of paracetamol if taken within 1 hour. Administer at least 1 hour before or 4-6 hours after cholestyramine. | Moderate |
Same composition (Paracetamol (650mg)), different brands: