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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) belonging to the fenamate class. It functions by inhibiting cyclooxygenase (COX) enzymes, thereby reducing prostaglandin synthesis.
## Primary Indications
* Short-term management of mild to moderate pain, including pain associated with dysmenorrhea.
* Symptomatic relief of osteoarthritis and rheumatoid arthritis (less common).
## Adult Dosing
* **Pain:** 500 mg every 4-6 hours as needed. Do not exceed 1500 mg in the first 24 hours or 750 mg per dose.
* **Dysmenorrhea:** 500 mg every 4-6 hours as needed, starting at the onset of pain and menstrual flow.
* **Arthritis:** Generally not recommended due to risk/benefit profile compared to other NSAIDs. If used, typically 500 mg three times daily.
## Pediatric Dosing
* **Pain/Dysmenorrhea:** Mefenamic acid is generally *not* recommended for children under 14 years of age due to limited data and potential for adverse effects.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Dose reduction may be necessary in patients with severe renal impairment.
* **Hepatic Impairment:** Use with caution. Dose reduction may be necessary in patients with severe hepatic impairment.
## Contraindications
* Hypersensitivity to mefenamic acid, aspirin, or other NSAIDs.
* History of bronchospasm, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Inflammatory bowel disease (active or history).
* Severe heart failure.
* Third trimester of pregnancy.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, dyspepsia, constipation, dizziness, headache.
* **Serious:** Gastrointestinal bleeding, ulceration, perforation; renal toxicity (including interstitial nephritis, papillary necrosis, and renal failure); cardiovascular thrombotic events (MI, stroke); hypersensitivity reactions; exacerbation of asthma; hepatic toxicity.
## Key Drug Interactions
* **Anticoagulants (e.g., warfarin):** Increased risk of bleeding. Monitor INR closely.
* **Corticosteroids:** Increased risk of GI ulceration and bleeding.
* **Other NSAIDs/Aspirin:** Increased risk of adverse effects, including GI bleeding.
* **ACE Inhibitors/ARBs:** May decrease antihypertensive effect and increase risk of renal impairment.
* **Diuretics:** May decrease diuretic effect and increase risk of renal impairment.
* **Lithium:** Increased serum lithium levels. Monitor lithium levels.
* **Methotrexate:** Increased risk of methotrexate toxicity.
## Monitoring
* **GI symptoms:** Assess for signs of bleeding or ulceration.
* **Renal function:** Monitor BUN and creatinine, especially in patients with pre-existing renal disease or those on concomitant nephrotoxic agents.
* **Hepatic function:** Monitor liver enzymes, especially with prolonged use.
* **Blood pressure:** NSAIDs can cause fluid retention and hypertension.
* **Signs of hypersensitivity:** Rash, itching, difficulty breathing.
## Clinical Pearls
* Mefenamic acid is typically for short-term use only.
* Administer with food or milk to minimize gastrointestinal upset.
* The 750 mg single dose maximum and 1500 mg 24-hour maximum should be strictly adhered to.
* Consider risk factors for GI bleeding (e.g., age, history of ulcers, concomitant medications) before initiating therapy.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional protocols for definitive guidance.*
