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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) belonging to the fenamate class. It exhibits analgesic, anti-inflammatory, and antipyretic properties. Its mechanism of action involves the inhibition of cyclooxygenase (COX) enzymes, thereby reducing prostaglandin synthesis.
## Primary Indications
* Mild to moderate pain (e.g., dental pain, postpartum pain)
* Primary dysmenorrhea
## Adult Dosing
* **Pain:** 500 mg every 6 hours as needed. Do not exceed 1500 mg in the first 24 hours of treatment, and do not exceed 1000 mg every 24 hours thereafter.
* **Primary Dysmenorrhea:** 500 mg every 6 hours starting at the onset of pain or bleeding, whichever comes first, for up to 3 days.
## Pediatric Dosing
Mefenamic acid is **not recommended** for use in children under 14 years of age due to lack of established safety and efficacy data.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Dose reduction may be necessary based on renal function. Data on specific dose adjustments are limited.
* **Hepatic Impairment:** Use with caution. Dose reduction may be necessary. Data on specific dose adjustments are limited.
* **Elderly:** Elderly patients may be more susceptible to adverse effects. Consider lower doses and closer monitoring.
## Contraindications
* Hypersensitivity to mefenamic acid, aspirin, 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.
* Inflammatory bowel disease (e.g., Crohn's disease, ulcerative colitis).
* Severe renal impairment.
* Severe hepatic impairment.
* Severe heart failure.
* Third trimester of pregnancy.
## Adverse Effects
Common adverse effects include gastrointestinal upset (nausea, vomiting, diarrhea, abdominal pain), dizziness, drowsiness, and rash. Serious adverse effects can include gastrointestinal bleeding, ulceration, perforation, cardiovascular thrombotic events (MI, stroke), renal impairment, hepatic injury, hypersensitivity reactions, and worsening of asthma.
## 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) / Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs):** Increased risk of gastrointestinal bleeding.
* **Other NSAIDs (including aspirin):** Increased risk of adverse effects, particularly gastrointestinal.
* **Diuretics and Antihypertensives:** May reduce efficacy and increase risk of renal toxicity.
* **Lithium:** Increased serum lithium levels.
* **Methotrexate:** Increased risk of methotrexate toxicity.
## Monitoring
* Signs and symptoms of gastrointestinal bleeding or ulceration.
* Renal function (BUN, creatinine) periodically, especially in patients with pre-existing renal disease.
* Liver function tests (LFTs) periodically, especially in patients with pre-existing hepatic disease.
* Blood pressure.
* Signs of cardiovascular events.
## Clinical Pearls
* Administer with food or milk to minimize gastrointestinal upset.
* Duration of use should be limited to the shortest effective period, generally not exceeding 7 days for pain and 3 days for dysmenorrhea, to minimize risks.
* Due to potential for central nervous system effects, caution patients about driving or operating machinery until they know how the drug affects them.
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**Disclaimer:** This information is intended for clinical decision support and does not replace professional medical judgment. Always refer to the most current prescribing information and consult with relevant healthcare professionals for individualized patient care.
