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# Mefenamic Acid
## Overview
Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) used for the short-term relief of mild to moderate pain. It is a weak acid and is thought to exert its effects by inhibiting cyclooxygenase (COX) enzymes, thereby reducing prostaglandin synthesis.
## Primary Indications
* Short-term treatment of mild to moderate pain, including menstrual pain (dysmenorrhea), dental pain, and post-operative pain.
## Adult Dosing
* **Pain:** 500 mg every 6 hours as needed. Do not exceed 1000 mg per dose or 4000 mg per day.
* **Dysmenorrhea:** 500 mg every 6 hours, starting at the onset of pain or bleeding and continuing for no more than 6 days.
## Pediatric Dosing
* Mefenamic acid is generally **not recommended** for children under 14 years of age due to limited data and potential for adverse effects. Some sources suggest doses of 6.5 mg/kg every 6 hours, but this is not universally established and should be approached with extreme caution and under expert guidance.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Data is limited, but reduced doses may be considered in severe impairment.
* **Hepatic Impairment:** Use with caution. Data is limited.
## Contraindications
* Known hypersensitivity to mefenamic acid, aspirin, or other NSAIDs.
* History of NSAID-induced bronchospasm, urticaria, or allergic-type reactions.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Active gastrointestinal bleeding or ulceration.
* Severe renal or hepatic impairment.
* Late pregnancy (third trimester).
## Adverse Effects
* **Common:** Diarrhea, nausea, vomiting, abdominal pain, dyspepsia, constipation.
* **Serious:** Gastrointestinal bleeding, ulceration, perforation; renal toxicity (including interstitial nephritis, papillary necrosis); hepatic dysfunction; cardiovascular thrombotic events; hypersensitivity reactions (including Stevens-Johnson syndrome, toxic epidermal necrolysis); anemia; headache; dizziness.
## Key Drug Interactions
* **Anticoagulants (e.g., warfarin):** Increased risk of bleeding.
* **Corticosteroids:** Increased risk of gastrointestinal ulceration and bleeding.
* **Diuretics and Antihypertensives:** May reduce their efficacy; increased risk of renal toxicity.
* **Lithium:** Increased serum lithium levels, potential for toxicity.
* **Methotrexate:** Increased risk of methotrexate toxicity.
* **Other NSAIDs/Salicylates:** Increased risk of adverse effects, particularly gastrointestinal.
## Monitoring
* **Gastrointestinal symptoms:** Watch for signs of bleeding (melena, hematemesis) or ulceration.
* **Renal function:** Monitor BUN and creatinine, especially in patients with pre-existing renal disease or those at risk.
* **Hepatic function:** Monitor LFTs, especially with long-term use or in patients with liver disease.
* **Blood pressure:** NSAIDs can cause fluid retention and hypertension.
* **Signs of hypersensitivity:** Rash, difficulty breathing.
## Clinical Pearls
* Mefenamic acid should be taken with food or milk to minimize gastrointestinal upset.
* It is generally recommended for short-term use only (up to 7 days) due to the risk of serious adverse effects, particularly gastrointestinal.
* Due to its short half-life, it is typically dosed every 6 hours.
* While effective for dysmenorrhea, other NSAIDs may have similar or superior efficacy.
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_This information is intended for healthcare professionals. Please consult the official prescribing information and relevant clinical guidelines for complete details and to verify current recommendations before initiating therapy._
