| MEFENAMIC ACID
Classifications: analgesic, nonsteroidal antiinflammatory drug (nsaid); antipyretic; Therapeutic: nsaid, analgesic; antipyretic
Pregnancy Category: C
250 mg tablets
NSAID that inhibits COX-1 and COX-2 enzymes necessary for prostaglandin synthesis. It affects platelet function.
Analgesic, antiinflammatory, and antipyretic actions.
Short-term relief of mild to moderate pain including primary dysmenorrhea.
Hypersensitivity to drug; GI inflammation, or ulceration. Safety in children <14 y, during pregnancy (category C) is not
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
- 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:
, 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:
Dyspnea; acute exacerbation of asthma; bronchoconstriction (in patients sensitive to aspirin).
Diagnostic Test Interference
False-positive reactions for urinary bilirubin (using diazo tablet test).
Mefenamic acid may prolong bleeding time with oral anticoagulants
may increase lithium
toxicity; increases pharmacologic and toxic activity of phenytoin, sulfonylureas
because of protein binding displacement. Herbal: Feverfew, garlic, ginger, ginkgo
increase bleeding potential.
Rapidly and completely from GI tract. Peak:
24 h. Duration:
6 h. Distribution:
Distributed in breast milk. Metabolism:
Partially in liver. Elimination:
50% in urine, 50% in feces. Half-Life:
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
Patient & Family Education
- Discontinue drug promptly if diarrhea, dark stools, hematemesis, ecchymoses, epistaxis, or rash occur and do not use again.
- 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.