Amifen® 500 mg Tablet: Each tablet contains Mefenamic Acid BP 500 mg.
Amifen® 60 ml Suspension: Each 5 ml contains Mefenamic Acid BP 50 mg.
Mefenamic Acid (Amifen®) is an analgesic preparation with anti-inflammatory properties. Mefenamic Acid is known to have a peripheral anti-inflammatory effect and has also shown antipyretic action.
Mode of action The pharmacological activity of Mefenamic Acid (Amifen®) may be due in part to its ability to inhibit the synthesis of prostaglandins. Mefenamic Acid also inhibits the action of exogenous prostaglandins on uterine muscle, uterine tube contraction and ovarian cyclic AMP and progesterone formation in animal models.
Pharmacokinetics Mefenamic Acid (Amifen®) is well absorbed from the gastro-intestinal tract. Peak plasma concentrations occur in about 2 to 4 hours, with a half-life of 2 to 4 hours. Plasma levels are proportional to dose, following multiple doses, with no drug accumulation.
Mefenamic Acid (Amifen®) is extensively bound to plasma proteins. Over 50% of the dose may be recovered in the urine as unchanged drug or conjugated metabolites.
The drug should not be continued for longer than 7 days.
Adults: 500 mg three times per day.
In menorrhagia the dosage is 500 mg three times a day beginning with the onset of menstrual flow and continuing for five days or until cessation of flow, whichever is less.
In primary dysmenorrhoea the dosage is 500 mg three times a day commencing at the onset of period pain and continued for up to three days while the symptoms persist.
Children (6 months and older): 25 mg/kg of body weight daily, in divided doses.
The doses may be repeated as necessary, up to three times daily.
Gastric irritation may be reduced by taking medication during meals.
Patients receiving an anticoagulant drug concurrently with mefenamic acid have had a prolongation of prothrombin time.
Patients receiving lithium concurrently with NSAIDs, have produced an elevation of plasma lithium levels and a reduction in renal lithium clearance. Thus, when mefenamic acid and lithium are administered concurrently, patients should be observed carefully for signs of lithium toxicity.
Over dosage Mefenamic acid has a marked tendency to induce tonic-clonic (grand mal) convulsions in over dosage. Dyskinesia, acute renal failure and coma have been reported. Over dose has led to fatalities. Treatment is symptomatic and supportive. Following accidental over dosage, the stomach should be emptied by inducing emesis or gastric lavage followed by administration of activated charcoal. Vital functions should be monitored and supported. Haemodialysis is of little value since mefenamic acid and its metabolites are firmly bound to plasma proteins.
Safety in pregnancy and lactation has not yet been established.
Caution should be exercised in the administration of mefenamic acid to patients suffering from dehydration and/or renal disease, particularly the elderly.
Bronchoconstriction may occur with mefenamic acid in asthmatic patients with aspirin sensitivity.
Mefenamic acid and its metabolites may give a false positive reaction to certain urine tests for the presence of bile.
Toxicity has also been seen in patients with pre renal condition leading to a reduction in renal blood flow or blood volume. Patients at greatest risk are those with impaired renal function, heart failure, liver dysfunction, those taking diuretics, and the elderly.
Store in a cool and dry place, protected from light.