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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) belonging to the fenamate class. It inhibits cyclooxygenase (COX) enzymes, reducing prostaglandin synthesis.
## Primary Indications
* Short-term management of mild to moderate pain.
* Primary dysmenorrhea.
## Adult Dosing
* **Pain:** 500 mg every 6 hours as needed. Maximum of 1500 mg per 24 hours for the first 48 hours, then 1000 mg per 24 hours thereafter.
* **Primary Dysmenorrhea:** 500 mg every 4 to 6 hours as needed. Maximum of 1500 mg per 24 hours for the first 48 hours, then 1000 mg per 24 hours thereafter.
Duration of use typically limited to 7 days.
## Pediatric Dosing
Mefenamic acid is generally **not recommended** for use in children under 14 years of age due to limited data and potential for serious adverse effects. Safety and efficacy have not been established.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Dose reduction may be necessary, especially in severe impairment.
* **Hepatic Impairment:** Use with caution. Monitor liver function. Dose reduction may be necessary.
* **Elderly:** Use with caution. Elderly patients are at increased risk of NSAID-related adverse effects. Consider a lower starting dose and longer interval between doses.
## Contraindications
* Known hypersensitivity to mefenamic acid or other NSAIDs.
* History of bronchospasm, asthma, allergic rhinitis, or urticaria precipitated by aspirin or other NSAIDs.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Active gastrointestinal (GI) bleeding or a history of GI bleeding or perforation related to prior NSAID use.
* Severe heart failure.
* Severe renal impairment (CrCl < 30 mL/min).
* Severe hepatic impairment.
* Third trimester of pregnancy.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, dyspepsia, constipation, dizziness, headache, rash.
* **Serious:**
* **GI:** Gastric or intestinal ulceration, bleeding, perforation.
* **Cardiovascular:** Myocardial infarction, stroke, hypertension, fluid retention, edema, heart failure.
* **Renal:** Acute kidney injury, interstitial nephritis, papillary necrosis.
* **Hepatic:** Hepatotoxicity, elevated liver enzymes.
* **Hematologic:** Anemia, leukopenia, thrombocytopenia.
* **Hypersensitivity:** Anaphylaxis, Stevens-Johnson syndrome, toxic epidermal necrolysis.
* **Other:** Bronchospasm, aseptic meningitis.
## Key Drug Interactions
* **Anticoagulants (e.g., warfarin):** Increased risk of bleeding. Monitor INR closely.
* **Antiplatelet agents (e.g., aspirin, clopidogrel):** Increased risk of bleeding.
* **Corticosteroids:** Increased risk of GI ulceration and bleeding.
* **Selective Serotonin Reuptake Inhibitors (SSRIs):** Increased risk of GI bleeding.
* **Lithium:** Increased lithium levels, potential for toxicity. Monitor lithium levels.
* **Methotrexate:** Increased methotrexate levels and toxicity.
* **Diuretics, ACE inhibitors, ARBs:** Reduced antihypertensive effect, increased risk of renal impairment.
* **Other NSAIDs:** Increased risk of GI toxicity and other adverse effects.
## Monitoring
* **Renal function:** Monitor serum creatinine and BUN, especially in patients with pre-existing renal disease, dehydration, or concomitant nephrotoxic agents.
* **Hepatic function:** Monitor liver enzymes (AST, ALT), especially in patients with hepatic impairment or a history of liver disease.
* **GI symptoms:** Assess for signs and symptoms of GI bleeding or ulceration.
* **Cardiovascular risk factors:** Assess for and manage underlying cardiovascular disease.
* **Blood pressure:** Monitor blood pressure, especially in patients with hypertension.
## Clinical Pearls
* Mefenamic acid should be taken with food or milk to minimize GI upset.
* Due to its short half-life, it is typically dosed every 4-6 hours.
* It is primarily eliminated by the kidneys, so caution is advised in renal impairment.
* Mefenamic acid has a higher incidence of GI side effects compared to some other NSAIDs.
* It is not typically a first-line agent for chronic pain due to the risk of GI and cardiovascular events with prolonged use.
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**Disclaimer:** This information is intended for clinical use and does not replace official prescribing information. Always consult the most current drug product labeling and institutional protocols for complete and up-to-date guidance.
