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# Mefenamic Acid
## Overview
Mefenamic acid is an anthranilic acid derivative nonsteroidal anti-inflammatory drug (NSAID). It exhibits analgesic, anti-inflammatory, and antipyretic properties via non-selective inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis.
## Primary Indications
* Treatment of mild to moderate pain.
* Management of primary dysmenorrhea.
* *Off-label:* Management of menorrhagia.
## Adult Dosing
* **Acute Pain/Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Maximum Duration:** Should not exceed 7 days of therapy.
## Pediatric Dosing
* **Children ≥14 years:** Use adult dosing (500 mg initially, then 250 mg every 6 hours).
* **Children <14 years:** Safety and efficacy have not been established. Use is generally not recommended.
## Dose Adjustments
* **Renal Impairment:** Avoid in patients with severe renal impairment (CrCl <30 mL/min). Use with caution in mild-to-moderate impairment; monitor renal function closely.
* **Hepatic Impairment:** Use with caution; not recommended in severe hepatic impairment.
* **Geriatric:** Use the lowest effective dose for the shortest duration due to increased risk of GI toxicity and renal impairment.
## Contraindications
* Hypersensitivity to mefenamic acid, aspirin, or other NSAIDs.
* History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* History of active peptic ulcer disease or gastrointestinal bleeding.
* Severe renal or hepatic failure.
## Adverse Effects
* **Common:** Abdominal pain, nausea, diarrhea (frequent), dizziness, headache.
* **Serious:** Gastrointestinal bleeding/perforation, myocardial infarction, stroke, new-onset or worsening hypertension, acute renal failure, fluid retention/edema, severe skin reactions (e.g., Stevens-Johnson Syndrome).
## Key Drug Interactions
* **Anticoagulants/Antiplatelets (e.g., Warfarin, Clopidogrel):** Increased risk of bleeding.
* **ACE Inhibitors/ARBs/Diuretics:** Increased risk of renal impairment and reduced antihypertensive efficacy.
* **Lithium:** May increase serum lithium concentrations (risk of toxicity).
* **Methotrexate:** May increase methotrexate toxicity via decreased renal clearance.
## Monitoring
* **Renal Function:** Periodic serum creatinine and BUN in long-term therapy or high-risk patients.
* **Blood Pressure:** Monitor regularly during initiation and dose changes.
* **GI Assessment:** Monitor for signs of gastrointestinal bleeding (e.g., anemia, melena, hematemesis).
* **Hematologic:** Monitor CBC if therapy duration exceeds 7 days.
## Clinical Pearls
* **Administration:** Take with food or milk to minimize gastrointestinal upset.
* **GI Risk:** Mefenamic acid has a higher incidence of diarrhea compared to other NSAIDs.
* **CV Risk:** Like all non-aspirin NSAIDs, it carries a boxed warning for increased risk of serious cardiovascular thrombotic events.
* **Pregnancy:** Avoid use, especially at ≥30 weeks gestation, due to premature closure of the fetal ductus arteriosus.
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**Educational Disclaimer:** This information is for educational purposes only and does not constitute medical advice. Dosing and clinical protocols may vary by institution and patient-specific factors. Always verify current prescribing information, local formulary guidelines, and patient-specific contraindications before prescribing or administering medication.
