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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) that exerts its effect primarily through the non-selective inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis. Its use is limited to short-term therapy due to gastrointestinal and renal toxicity risks.
## Primary Indications
* Treatment of primary dysmenorrhea.
* Short-term management of mild to moderate pain (usually ≤7 days).
## Adult Dosing
* **Dysmenorrhea/Mild-to-Moderate Pain:** 500 mg orally as an initial dose, followed by 250 mg every 6 hours as needed.
* **Maximum Duration:** Should not exceed 7 days of continuous therapy.
## Pediatric Dosing
* **Children ≥14 years:** Dosing is identical to the adult regimen (500 mg initial, then 250 mg q6h prn, max 7 days).
* **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. If used in chronic hepatic disease, initiate at the lowest effective dose.
## Contraindications
* Known hypersensitivity to mefenamic acid or aspirin/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.
* Active peptic ulcer disease or gastrointestinal bleeding.
* Severe renal or hepatic failure.
## Adverse Effects
* **Gastrointestinal:** Diarrhea (common), nausea, dyspepsia, abdominal pain, GI ulceration/perforation.
* **Renal:** Fluid retention, edema, acute renal failure, interstitial nephritis.
* **Cardiovascular:** Hypertension, increased risk of myocardial infarction or stroke (class effect of NSAIDs).
* **Hematologic:** Anemia, prolonged bleeding time.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding due to antiplatelet effects and GI mucosal injury.
* **ACE Inhibitors/ARBs/Diuretics:** Increased risk of renal impairment and diminished antihypertensive efficacy.
* **Lithium/Methotrexate:** NSAIDs may decrease clearance, leading to potential toxicity.
* **Other NSAIDs/Corticosteroids:** Increased risk of GI toxicity.
## Monitoring
* **Baseline/Intermittent:** Renal function (BUN/SCr), electrolytes, and blood pressure.
* **Symptomatic:** Signs of occult GI bleeding (e.g., melena, fatigue), unexplained weight gain, or edema.
* **Long-term (unadvised):** CBC to monitor for anemia.
## Clinical Pearls
* **Diarrhea:** Mefenamic acid is uniquely more associated with diarrhea than other NSAIDs; discontinue if severe diarrhea occurs.
* **Administration:** Administer with food or milk to minimize gastrointestinal irritation.
* **Cardiovascular Risk:** As with all NSAIDs, use the lowest effective dose for the shortest duration possible to mitigate cardiovascular and gastrointestinal risks.
* **Pediatric Caution:** Do not use for common pediatric fevers or viral illness, as safer alternatives (acetaminophen, ibuprofen) are preferred.
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**Educational Disclaimer:** This information is for educational purposes only and does not constitute medical advice. Prescribing practices may vary based on local guidelines and institutional protocols. Always verify current prescribing information, contraindications, and drug interactions using official local pharmacopeia or verified clinical databases (e.g., Lexicomp, UpToDate) before prescribing or administering medication.
