MEFENAMIC ACID
| MEFENAMIC ACID (me-fe-nam'ik) Ponstel Classifications: analgesic, nonsteroidal antiinflammatory drug (nsaid); antipyretic; Therapeutic: nsaid, analgesic; antipyretic Prototype: Ibuprofen Pregnancy Category: C |
Availability
250 mg tablets
Action
NSAID that inhibits COX-1 and COX-2 enzymes necessary for prostaglandin synthesis. It affects platelet function.
Therapeutic Effect
Analgesic, antiinflammatory, and antipyretic actions.
Uses
Short-term relief of mild to moderate pain including primary dysmenorrhea.
Contraindications
Hypersensitivity to drug; GI inflammation, or ulceration. Safety in children <14 y, during pregnancy (category C) is not established.
Cautious Use
History of kidney or liver disease; blood dyscrasias; asthma; cardiac arrhythmias; CHF; edema; diabetes mellitus; SLE; hypersensitivity to aspirin. Long term use increases risk of serious adverse events (see DRUG INTERACTIONS).
Route & Dosage
| Mild to Moderate Pain Adult: PO Loading Dose 500 mg PO Maintenance Dose 250 mg q6h prn |
Administration
Oral- Give with meals, food, or milk to minimize GI adverse effects.
- Do not use drug for a period exceeding 1 wk (manufacturer's warning).
Adverse Effects (≥1%)
CNS: Drowsiness, insomnia, dizziness, nervousness, confusion, headache. GI: Severe diarrhea, ulceration, and bleeding; nausea, vomiting, abdominal cramps, flatus, constipation, hepatic toxicity. Hematologic: Prolonged prothrombin time, severe autoimmune hemolytic anemia (long-term use), leukopenia, eosinophilia, agranulocytosis, thrombocytopenic purpura, megaloblastic anemia, pancytopenia, bone marrow hypoplasia. Urogenital: Nephrotoxicity, dysuria, albuminuria, hematuria, elevation of BUN. Skin: Urticaria, rash, facial edema. Special Senses: Eye irritation, loss of color vision (reversible), blurred vision, ear pain. Body as a Whole: Perspiration. CV: Palpitation. Respiratory: Dyspnea; acute exacerbation of asthma; bronchoconstriction (in patients sensitive to aspirin).Diagnostic Test Interference
False-positive reactions for urinary bilirubin (using diazo tablet test).
Interactions
Drug: Mefenamic acid may prolong bleeding time with oral anticoagulants, heparin; may increase lithium toxicity; increases pharmacologic and toxic activity of phenytoin, sulfonylureas, sulfonamides, warfarin because of protein binding displacement. Herbal: Feverfew, garlic, ginger, ginkgo increase bleeding potential.Pharmacokinetics
Absorption: Rapidly and completely from GI tract. Peak: 2–4 h. Duration: 6 h. Distribution: Distributed in breast milk. Metabolism: Partially in liver. Elimination: 50% in urine, 50% in feces. Half-Life: 2 h.Nursing Implications
Assessment & Drug Effects
- Assess patients who develop severe diarrhea and vomiting for dehydration and electrolyte imbalance.
- Lab tests: With long-term therapy (not recommended) obtain periodic complete blood counts, Hct and Hgb, and kidney function tests.
Patient & Family Education
- Discontinue drug promptly if diarrhea, dark stools, hematemesis, ecchymoses, epistaxis, or rash occur and do not use again. Contact physician.
- Notify physician if persistent GI discomfort, sore throat, fever, or malaise occur.
- Do not drive or engage in potentially hazardous activities until response to drug is known. It may cause dizziness and drowsiness.
- Monitor blood glucose for loss of glycemic control if diabetic.
Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; 
Canadian drug name; 
Prototype drug