Mefenamic

Uses

Mefenamic is used in mild to moderate pain including headache, dental pain, postoperative and postpartum pain, dysmenorrhoea, menorrhagia, in musculoskeletal and joint disorders such as osteoarthritis and rheumatoid arthritis; and in children with fever and juvenile idiopathic arthritis.

Mefenamic is also used to associated treatment for these conditions: Mild pain, Primary Dysmenorrhoea, Gastrointestinal cramps, Moderate Pain

How Mefenamic works

Mefenamic binds the prostaglandin synthetase receptors COX-1 and COX-2, inhibiting the action of prostaglandin synthetase. As these 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.

Dosage

Mefenamic dosage

As with other NSAIDs, the lowest dose should be sought for each patient. Therefore, after observing the response to initial therapy with Mefenamic, the dose and frequency should be adjusted to suit an individual patient's needs.Administration is by the oral route, preferably with food.

• Adult: A 500 mg dose should be given to adults up to three times (1.5 g total) per day.
• Infants over 6 months: 25 mg/kg of body weight daily in divided doses for not longer than 7 days.

Side Effects

In patients taking Mefenamic or other NSAIDs, the most frequently reported adverse experiences include : abdominal pain, constipation, diarrhoea, dyspepsia, flatulence, gross bleeding/perforation, heartburn, nausea, GI ulcers, vomiting, abnormal renal function, anaemia, dizziness, oedema, elevated liver enzymes, headache, increased bleeding time, pruritus, rash and tinnitus.

Toxicity

Oral, rat LD₅₀: 740 mg/kg. Symptoms of overdose may include severe stomach pain, coffee ground-like vomit, dark stool, ringing in the ears, change in amount of urine, unusually fast or slow heartbeat, muscle weakness, slow or shallow breathing, confusion, severe headache or loss of consciousness.

Precaution

NSAIDs should be prescribed with extreme caution in those with a prior history of ulcer disease or gastrointestinal bleeding. To minimise the potential risk for an adverse GI event, the lowest effective dose should be used for the shortest possible duration. In cases with pre-existing advanced kidney disease, treatment with Mefenamic is not recommended.

Interaction

Concomitant use with CYP2C9 isoenzyme inhibitors may alter safety and efficacy of mefenamic acid. May enhance methotrexate toxicity. Reduced BP response to ACE inhibitors or angiotensin II receptor antagonists. Increased risk of serious GI events with aspirin. May reduce the natriuretic effects of furosemide or thiazide diuretics. Reduced renal lithium clearance and elevated plasma lithium levels. May enhance anticoagulant effect of warfarin.

Food Interaction

• Avoid alcohol.
• Take with food.

Volume of Distribution

• 1.06 L/kg [Normal Healthy Adults (18-45 yr)]

Elimination Route

Mefenamic is rapidly absorbed after oral administration.

Half Life

2 hours

Clearance

• Oral cl=21.23 L/hr [Healthy adults (18-45 yrs)]

Elimination Route

The fecal route of elimination accounts for up to 20% of the dose, mainly in the form of unconjugated 3-carboxymefenamic acid.3 The elimination half-life of mefenamic acid is approximately two hours. Mefenamic, its metabolites and conjugates are primarily excreted by the kidneys. Both renal and hepatic excretion are significant pathways of elimination.

Pregnancy & Breastfeeding use

Pregnancy: In late pregnancy, as with other NSAIDs, Mefenamic should be avoided because it may cause premature closure of the ductus arteriosus. In general there are no adequate and well controlled studies in pregnant women. Mefenamic should be used during pregnancy only if the potential benefit justifies the potential risk to the foetus. Rated as Pregnancy Category C.

Lactation: Trace amounts of Mefenamic may be present in breast milk. Taking into account the importance of the drug to the mother , decision should be made whether to discontinue nursing or to discontinue the drug.

Contraindication

Mefenamic is contraindicated in patients with known hypersensitivity to Me Mefenamic acid. Mefenamic should not be given to patients who have experienced asthma, urticaria, or allergic type reactions after taking aspirin or other NSAIDs. Rarely fatal, anaphylactic like reactions to NSAIDs have been reported in such patients. Mefenamic is contraindicated in patients with active ulceration or chronic inflammation of upper gastrointestinal tract and should not be used in patients with preexisting renal disease.

Acute Overdose

Symptoms: Headache, nausea, vomiting, epigastric pain, GI bleeding. Rarely, diarrhoea, disorientation, excitation, coma, drowsiness, tinnitus, fainting, and occasionally convulsions.

Management: Symptomatic and supportive treatment. In acute overdosage, empty the stomach immediately by inducing emesis or by gastric lavage followed by admin of activated charcoal.

Storage Condition

Store between 20-25° C.

Innovators Monograph

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