Mefenamic acid is a non-steroidal anti-inflammatory drug (NSAID) of the fenamate class, used primarily for its analgesic and antipyretic properties. It is a potent inhibitor of cyclooxygenase (COX) enzymes, thereby reducing prostaglandin synthesis. In the Indian context, it is widely prescribed for short-term management of acute pain, particularly dysmenorrhea, dental pain, and post-operative pain, due to its rapid onset and effectiveness. It is available as an over-the-counter (OTC) medicine in lower strengths, but the 500mg strength typically requires a prescription.
Adult: For pain: 500 mg as an initial dose, followed by 250 mg every 6 hours as needed. Maximum daily dose: 1500 mg. For dysmenorrhea: 500 mg as a loading dose, then 250 mg every 6 hours. Start with the onset of menses, not to exceed 2-3 days.
Note: Take with food or a full glass of milk to minimize gastrointestinal upset. Swallow the tablet whole with water. Do not crush or chew. Should be used for the shortest duration possible, typically not exceeding 7 days for pain unless directed by a physician.
Mefenamic acid is a non-selective, reversible inhibitor of cyclooxygenase (COX-1 and COX-2) enzymes. This inhibition blocks the conversion of arachidonic acid to prostaglandin G2 and subsequently to prostaglandin H2, the precursors of various prostaglandins (PGs), thromboxanes, and prostacyclins. The reduction in prostaglandin synthesis, particularly in peripheral tissues and the central nervous system, mediates its analgesic, anti-inflammatory, and antipyretic effects.
Pregnancy: Category C (first and second trimester): Use only if potential benefit justifies potential risk to the fetus. Avoid in third trimester (Category D) due to risk of premature closure of the fetal ductus arteriosus, delayed labor, and potential renal dysfunction in the neonate.
Driving: May cause dizziness, drowsiness, or blurred vision. Patients should be cautioned about operating machinery or driving until they know how the drug affects them.
| Warfarin/Acenocoumarol | Increased risk of bleeding due to displacement from protein binding and antiplatelet effect of NSAIDs. | Major |
| Aspirin (low-dose) | May antagonize antiplatelet effect of aspirin. Increased GI toxicity. | Moderate |
| Other NSAIDs (e.g., Diclofenac, Ibuprofen) | Increased risk of GI toxicity and renal impairment without added benefit. | Major |
| Lithium | Decreased renal clearance of lithium, leading to increased lithium levels and toxicity. | Major |
| Methotrexate | Decreased renal clearance of methotrexate, increasing its toxicity, especially at high doses. | Major |
| ACE Inhibitors (e.g., Ramipril, Enalapril) / ARBs (e.g., Telmisartan) | Reduced antihypertensive effect. Increased risk of renal impairment. | Moderate |
| Diuretics (e.g., Furosemide, Hydrochlorothiazide) | Reduced diuretic and antihypertensive efficacy. Risk of renal failure. | Moderate |
| Corticosteroids (e.g., Prednisolone) | Markedly increased risk of GI ulceration and bleeding. | Major |
| Selective Serotonin Reuptake Inhibitors (SSRIs) e.g., Sertraline | Increased risk of upper GI bleeding. | Moderate |
| Cyclosporine | Increased risk of nephrotoxicity. | Major |
Same composition (Mefenamic Acid (500mg)), different brands: