Mefenamic Acid

A to Z Drug Facts

(MEH-fen-AM-ik acid)

Ponstel,  Ponstan

Class: Analgesic/NSAID

 Action Decreases inflammation, pain and fever, probably through inhibition of cyclooxygenase activity and prostaglandin synthesis.

 Indications Relief of moderate pain lasting < 1 wk; treatment of primary dysmenorrhea. Unlabeled use(s): Treatment of sunburn, migraine (acute attack), PMS.

 Contraindications Patients in whom aspirin, iodides or any NSAID has caused allergic-type reactions; preexisting renal disease; active ulceration or chronic inflammation of GI tract.

 Route/Dosage

Acute Pain

ADULTS & CHILDREN > 14 YR: PO 500 mg, followed by 250 mg q 6 hr prn. Usually not used longer than 1 wk.

Primary Dysmenorrhea

ADULTS & CHILDREN > 14 YR: PO 500 mg, followed by 250 mg q 6 hr starting with onset of bleeding and associated symptoms.

 Interactions

Anticoagulants: Increased risk of gastric erosion and bleeding. Cyclosporine: Nephrotoxicity of both agents may be increased. Cytochrome P450: Exercise caution when coadministering mefenamic acid with drugs known to inhibit the isoenzyme 2C9. Lithium: Serum lithium levels may be increased. Methotrexate: Increased methotrexate levels. Salicylates: Additive GI toxicity.

 Lab Test Interferences May cause prolonged bleeding time or false-positive reaction for urinary bile using diazo tablet test.

 Adverse Reactions

CV: Edema; weight gain; CHF; altered BP; palpitations; chest pain; radycardia; tachycardia. CNS: Headache; vertigo; drowsiness; dizziness; insomnia. DERM: Rash; urticaria; purpura. EENT: Blurred vision; tinnitus; salivation; glossitis. GI: Diarrhea; dry mouth; vomiting; abdominal pain; dyspepsia; GI bleeding; ausea; constipation; flatulence. GU: Hematuria; proteinuria; dysuria; renal failure. HEMA: Decreased hematocrit; bleeding; neutropenia; leukopenia; pancytopenia; osinophilia; thrombocytopenia. HEPA: Mild elevations in liver function test results. RESP: Bronchospasm; laryngeal edema; rhinitis; dyspnea; pharyngitis; emoptysis; shortness of breath. OTHER: Autoimmune hemolytic anemia may occur if used long term.

 Precautions

Pregnancy: Category C. Lactation: Undetermined. Children: Not recommended for children < 14 yr. Elderly: Increased risk of adverse reactions. Diarrhea: If diarrhea occurs, reduce dosage or temporarily discontinue. GI toxicity: Bleeding, ulceration, or perforation can occur at any time, with or without warning symptoms. Hypersensitivity: May occur; use with caution in aspirin-sensitive individuals because of possible cross sensitivity. Rash: Promptly discontinue if rash develops. Renal effects: Acute renal insufficiency, interstitial nephritis, hyperkalemia, hyponatremia and renal papillary necrosis may occur. Renal impairment: Lower doses may be necessary.

 Administration/Storage

• Administer with meals, followed by full glass of water or milk to avoid GI and esophageal irritation. May be given with antacids if stomach upset occurs.
• Exercise caution when initiating treatment in patients with considerable dehydration. Rehydrate patients first and then start therapy with mefenamic acid.
• Store at room temperature in tightly closed, light-resistant container.

 Assessment/Interventions

• Obtain patient history, including drug history and any known allergies. Note chronic alcohol use, fluid retention, nasal polyps, bronchospastic disease or hypersensitivity to aspirin or NSAIDs.
• Weigh patient daily if fluid retention is a concern.
• Monitor carefully for hypersensitivity. Note any ecchymosis or rash.
• Monitor renal and liver function and blood studies throughout treatment.
• Monitor for diarrhea or blood in stools. If diarrhea occurs, notify physician. Dosage may need to be reduced or drug temporarily withheld.
• Notify physician if stomach pain develops or continues.

 Patient/Family Education

• Inform patient not to use drug for more than 1 wk. If given for dysmenorrhea, instruct patient to begin taking drug with onset of bleeding and associated symptoms.
• Warn patient about potential for bleeding and advise to notify other health care professionals that drug is being taken.
• Advise patient to discontinue medication if rash develops and to contact physician.
• Instruct patient to report these symptoms to physician: rash, visual problems, dark stools, decreased urinary output, persistent headache or stomach pain and unusual bruising or bleeding.
• Advise patient to avoid intake of alcoholic beverages.
• Instruct patient that drug may cause drowsiness and to use caution while driving or performing other activities requiring mental alertness.
• Caution patient to avoid prolonged exposure to sunlight and to use sunscreen or wear protective clothing to avoid photosensitivity reaction.
• Instruct patient not to take otc medications, including aspirin and ibuprofen or other prescription drugs, without consulting physician.

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Copyright © 2003 Facts and Comparisons
David S. Tatro
A to Z Drug Facts