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Mefenamic Acid Mefenamic Acid
Mefenamic Acid Mefenamic Acid

Mefenamic acid is a non-steroidal anti-inflammatory drug (NSAID). 

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Mefenamic acid is a non-steroidal anti-inflammatory drug (NSAID). It may block certain substances in the body that are linked to inflammation. NSAIDs treat the symptoms of pain and inflammation, menstrual pain and may be used for short term (not more than 7 days) for treating mild to moderate pain surgery.

Pharmacological class: NSAID


  • Menstrual pain (Primary dysmenorrhea)
  • Pain and inflammation
  • Rheumatoid arthritis
  • Osteoarthritis
  • Fever

Pharmachologic action

Mefenamic acid acts by inhibiting the prostaglandin synthetase, that is, cyclooxygenase enzymes (COX-1 and COX-2). Hence, it prevents the release of the inflammatory mediators. As these prostaglandin receptors have a role as a major mediator of inflammation and/or a role for prostanoid signaling in activity-dependent plasticity, the symptoms of pain are temporarily reduced.


Pain: 500 mg orally followed by 250 mg every 6 hours as needed, not to exceed 7 days

Dysmenorrhea: 500 mg orally followed by 250 mg every 6 hours starting with the onset of menses

Pediatric Dose for Pain: 14 to 18 years: 500 mg orally followed by 250 mg every 6 hours as needed, not to exceed 7 days


Mefenamic Acid is rapidly absorbed after oral administration. It has been reported that mefenamic acid as binds greater than 90% to the albumin. The apparent volume of distribution estimated following a 500-mg oral dose of mefenamic Acid is 1.06 L/kg. Mefenamic Acid is metabolized by cytochrome P450 enzyme CYP2C9 to 3-hydroxymethyl mefenamic acid (Metabolite I). Mefenamic Acid gets glucuronidated directly. Approximately 52% of mefenamic acid dose is excreted into the urine primarily as glucuronides of mefenamic acid (6%), 3-hydroxymefenamic acid (25%) and 3-carboxymefenamic acid (21%). The fecal route of elimination accounts for up to 20% of the dose, mainly in the form of unconjugated 3-carboxymefenamic acid.


  • In patients with known hypersensitivity to Mefenamic Acid
  • In patients who have experienced asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs
  • Contraindicated for the treatment of peri-operative pain in the setting of coronary artery bypass graft (CABG) surgery
  • In patients with acute active ulceration or chronic inflammation of either the upper or lower gastrointestinal tract
  • In patients with pre-existing renal disease

Drug interaction

  • Mefenamic acid when administered with aspirin, its protein binding is reduced and the potential of adverse effects gets increased
  • Mefenamic acid can reduce the natriuretic effect-of furosemide and thiazides when taken concomitantly
  • NSAIDs causes an elevation of plasma lithium levels and a reduction in renal lithium clearance so causes lithium toxicity
  • Users of NSAIDs and warfarin have a risk of serious GI bleeding
  • Mefenamic acid administered concomitantly with methotrexate enhance the toxicity of methotrexate

Side effects

Common (affecting between 1 in 10 to 1 in 100):

  • Constipation
  • Diarrhea
  • Dizziness
  • Gas
  • Headache
  • Heartburn
  • Nausea
  • Stomach upset
  • Dyspepsia
  • Flatulence


Uncommon (affecting 1 in 100 to 1 in 1000):

  • Fever
  • Infection
  • Sepsis
  • Blurred vision


Very rare (affecting less than 1 in 10,000):

  • Congestive heart failure
  • Hypertension
  • Asthma
  • Dyspnea
  • Arrhythmia
  • Hypotension


  • Avoid in patients with pre-existing asthma or aspirin sensitivity
  • Avoid in patients having coagulation disorders or patients receiving anticoagulants
  • Avoid in patients having liver dysfunction, or an abnormal liver test as severe hepatic reactions may occur

Clinical evidence

In a recent study, thirty-five patients (16--23 years old) who had severe primary dysmenorrhea were treated with 500 mg of mefenamic acid every eight hours for a maximum of three days during menstruation for three consecutive cycles. A total of 194 treated cycles were evaluated, 110 cycles with mefenamic acid and 84 with placebo. Mefenamic acid produced complete relief of all the symptoms of dysmenorrhea in 31 (88.6%) patients in all 98 treated cycles and, in another two patients, moderate relief in five of the six cycles. It is concluded that mefenamic acid is safe and effective in most of patients with primary dysmenorrhea and represents a rational short-term therapy for this syndrome.1


    1. Int J Gynaecol Obstet. 1980;18(3):172-5.
    2. http://www.rxlist.com/ponstel-drug/side-effects-interactions.htm
    3. http://www.drugs.com/cdi/mefenamic-acid.html
    4. https://www.nlm.nih.gov/medlineplus/druginfo/meds/a681028.html
    5. http://www.healthline.com/drugs/mefenamic-acid/oral-capsule#Dosage4

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