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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) of the fenamate class used for the short-term treatment of mild to moderate pain. It works by inhibiting cyclooxygenase (COX) enzymes, reducing prostaglandin synthesis.
## Primary Indications
* Short-term treatment of mild to moderate pain, particularly associated with menstruation (dysmenorrhea).
* Relief of pain in osteoarthritis and rheumatoid arthritis (though not typically a first-line agent for chronic arthritis due to a less favorable risk-benefit profile compared to other NSAIDs).
## Adult Dosing
* **Pain:** 500 mg every 4-6 hours as needed. Maximum daily dose is 1500 mg. Treatment duration typically should not exceed 7 days.
* **Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed.
## Pediatric Dosing
* Mefenamic acid is generally not recommended for use in children under 14 years of age due to lack of established safety and efficacy.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Dose reduction may be necessary in severe impairment.
* **Hepatic Impairment:** Use with caution. Dose reduction may be necessary in severe impairment.
* **Elderly:** Increased risk of adverse effects. Consider lower doses and closer monitoring.
## Contraindications
* Hypersensitivity to mefenamic acid, aspirin, or other NSAIDs.
* History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs.
* Peri-operative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Active gastrointestinal bleeding or history of recurrent gastrointestinal perforation or ulceration.
* Severe renal, hepatic, or cardiac impairment.
* Late pregnancy (third trimester).
## Adverse Effects
* **Common:** Diarrhea, nausea, vomiting, abdominal pain, constipation, dyspepsia, rash, dizziness, headache, tinnitus.
* **Serious:** Gastrointestinal bleeding, ulceration, and perforation; renal impairment/failure; hepatic dysfunction; cardiovascular thrombotic events (myocardial infarction, stroke); hypersensitivity reactions (including anaphylaxis); exacerbation of asthma; fluid retention and edema.
## Key Drug Interactions
* **Anticoagulants (e.g., warfarin):** Increased risk of bleeding. Monitor INR closely.
* **Corticosteroids:** Increased risk of gastrointestinal ulceration and bleeding.
* **Selective Serotonin Reuptake Inhibitors (SSRIs) and Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs):** Increased risk of gastrointestinal bleeding.
* **ACE inhibitors, Angiotensin II Receptor Blockers (ARBs), Diuretics:** Reduced antihypertensive effect and increased risk of renal impairment.
* **Lithium:** Increased serum lithium levels and risk of toxicity.
* **Methotrexate:** Increased risk of methotrexate toxicity.
## Monitoring
* **Renal function:** Baseline and periodic monitoring, especially in patients with pre-existing renal disease or those at risk.
* **Hepatic function:** Baseline and periodic monitoring.
* **Gastrointestinal symptoms:** Patients should be advised to report any signs of bleeding or ulceration (e.g., black, tarry stools; severe stomach pain; vomiting blood).
* **Blood pressure:** NSAIDs can elevate blood pressure.
## Clinical Pearls
* Mefenamic acid is intended for short-term use only.
* Administer with food or milk to minimize gastrointestinal upset.
* Due to the risk of diarrhea, patients should be monitored for dehydration, especially in pediatric patients if used off-label.
* Mefenamic acid can mask signs of infection.
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*Disclaimer: This information is intended for healthcare professionals. Always verify current prescribing information with the official product monograph or a reliable drug information resource before making clinical decisions.*
