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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
* Mild to moderate pain, particularly associated with menstruation (dysmenorrhea).
* Rheumatoid arthritis and osteoarthritis (less commonly used than other NSAIDs).
## Adult Dosing
* **Pain:** 500 mg every 6 to 8 hours as needed.
* **Dysmenorrhea:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Rheumatoid Arthritis/Osteoarthritis:** Dosing is highly variable and generally not preferred; typically starts at 250 mg three to four times daily and may be increased cautiously.
* **Maximum:** Not to exceed 1000 mg in a single dose or 4000 mg per day.
## Pediatric Dosing
Mefenamic acid is generally not recommended for use in children under 14 years of age due to limited safety and efficacy data.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Dosage reduction may be necessary in severe impairment, although specific guidelines are not well established.
* **Hepatic Impairment:** Use with caution. Dosage reduction may be necessary, although specific guidelines are not well established.
* **Elderly:** Increased risk of adverse effects, particularly gastrointestinal bleeding and renal toxicity. Consider a lower starting dose and monitor closely.
## Contraindications
* Hypersensitivity to mefenamic acid, aspirin, or other NSAIDs.
* History of bronchospasm, asthma, 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 renal impairment.
* Severe hepatic impairment.
* Severe heart failure.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal pain, constipation, dyspepsia, rash.
* **Serious:** Gastrointestinal bleeding, ulceration, perforation; cardiovascular thrombotic events (myocardial infarction, stroke); renal failure; hepatotoxicity; hypersensitivity reactions; exacerbation of asthma.
## Key Drug Interactions
* **Anticoagulants (e.g., warfarin):** Increased risk of bleeding.
* **Corticosteroids:** Increased risk of gastrointestinal ulceration and bleeding.
* **Selective Serotonin Reuptake Inhibitors (SSRIs) & Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs):** Increased risk of bleeding, particularly gastrointestinal.
* **Diuretics & Antihypertensives (e.g., ACE inhibitors, ARBs, beta-blockers):** NSAIDs can reduce their efficacy and increase the risk of renal impairment.
* **Lithium:** NSAIDs can increase lithium levels, leading to toxicity.
* **Methotrexate:** NSAIDs can increase methotrexate levels and toxicity.
## Monitoring
* **Renal function:** Baseline and periodically, especially in patients with pre-existing renal disease or those at risk.
* **Hepatic function:** Baseline and periodically, especially in patients with pre-existing liver disease.
* **Complete blood count (CBC):** To monitor for anemia or other hematologic changes, particularly with long-term use.
* **Signs and symptoms of gastrointestinal bleeding:** Hematemesis, melena, abdominal pain.
* **Blood pressure:** NSAIDs can cause or worsen hypertension.
## Clinical Pearls
* Mefenamic acid has a relatively short half-life, necessitating frequent dosing.
* It is often preferred for dysmenorrhea due to its rapid onset of action and effectiveness.
* Should be taken with food or milk to minimize gastrointestinal upset.
* Due to the risk of serious cardiovascular and gastrointestinal events, use the lowest effective dose for the shortest duration necessary.
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**Disclaimer:** This information is intended for healthcare professionals and does not replace the need to consult the official prescribing information or other relevant clinical resources before making any treatment decisions. Always verify current drug information.
