Mefenamic-Acid

MEFENAMIC-ACID- mefenamic acid capsule
SCIELE PHARMA INC

MEFENAMIC ACID CAPSULES, USP 250 mg Rev. 08/07 Rx Only MEF-PI-2

Cardiovascular Risk

  • NSAIDs may cause an increased risk of serious cardiovascular thrombotic events, myocardial infarction, and stroke, which can be fatal. This risk may increase with duration of use. Patients with cardiovascular disease or risk factors for cardiovascular disease may be at greater risk (See WARNINGS).
  • MEFENAMIC ACID is contraindicated for the treatment of peri-operative pain in the setting of coronary artery bypass graft (CABG) surgery (See WARNINGS).

Gastrointestinal Risk

  • NSAIDs cause an increased risk of serious gastrointestinal adverse events including bleeding, ulceration, and perforation of the stomach or intestines, which can be fatal. These events can occur at any time during use and without warning symptoms. Elderly patients are at greater risk for serious gastrointestinal events (See WARNINGS).

DESCRIPTION

MEFENAMIC ACID is a member of the fenamate group of nonsteroidal anti-inflammatory drugs (NSAIDs). Each blue-banded, ivory capsule contains 250 mg of mefenamic acid for oral administration. Mefenamic acid is a white to greyish-white, odorless, microcrystalline powder with a melting point of 230°-231°C and water solubility of 0.004% at pH 7.1. The chemical name is N-2,3-xylylanthranilic acid. The molecular weight is 241.29. Its molecular formula is C15 H15 N02 and the structural formula of mefenamic acid is: Image from Drug Label Content Each capsule also contains lactose, NF. The capsule shell and/or band contains citric acid, USP; D&C yellow No. 10; FD&C blue No. 1; FD&C red No. 3; FD&C yellow No. 6; gelatin, NF; glycerol monooleate; silicon dioxide, NF; sodium benzoate, NF; sodium lauryl sulfate, NF; titanium dioxide, USP.

CLINICAL PHARMACOLOGY

Pharmacodynamics

MEFENAMIC ACID is a non-steroidal anti-inflammatory drug (NSAID) that exhibits anti-inflammatory, analgesic, and antipyretic activities in animal models. The mechanism of action of MEFENAMIC ACID, like that of other NSAIDs, is not completely understood but may be related to prostaglandin synthetase inhibition.

Pharmacokinetics

Absorption: Mefenamic acid is rapidly absorbed after oral administration. In two 500-mg single oral dose studies, the mean extent of absorption was 30.5 mcg/hr/mL (17%CV).1,2 The bioavailability of the capsule relative to an IV dose or an oral solution has not been studied. Following a single 1-gram oral dose, mean peak plasma levels ranging from 10-20 mcg/mL3 have been reported. Peak plasma levels are attained in 2 to 4 hours and the elimination half-life approximates 2 hours. Following multiple doses, plasma levels are proportional to dose with no evidence of drug accumulation. In a multiple dose trial of normal adult subjects (n=6) receiving 1-gram doses of mefenamic acid four times daily, steady-state concentrations of 20 mcg/mL were reached on the second day of administration, consistent with the short half-life. The effect of food on the rate and extent of absorption of mefenamic acid has not been studied. Concomitant ingestion of antacids containing magnesium hydroxide has been shown to significantly increase the rate and extent of mefenamic acid absorption (see PRECAUTIONS, Drug Interactions).1 Distribution: Mefenamic acid has been reported as being greater than 90% bound to albumin.9 The relationship of unbound fraction to drug concentration has not been studied. The apparent volume of distribution (Vzss /F) estimated following a 500-mg oral dose of mefenamic acid was 1.06 L/kg.2 Based on its physical and chemical properties, MEFENAMIC ACID is expected to be excreted inhuman breast milk. Metabolism: Mefenamic acid is metabolized by cytochrome P450 enzyme CYP2C9 to 3-hydroxymethyl mefenamic acid (Metabolite l). Further oxidation to a 3-carboxymefenamic acid (Metabolite ll) may occur.10 The activity of these metabolites has not been studied. The metabolites may undergo glucuronidation and mefenamic acid is also glucuronidated directly. A peak plasma level approximating 20 mcg/mL was observed at 3 hours for the hydroxy metabolite and its glucuronide (n=6) after a single 1-gram dose. Similarly, a peak plasma level of 8 mcg/mL was observed at 6-8 hours for the carboxy metabolite and its glucuronide.3 Excretion: Approximately fifty-two percent of a 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.3 The elimination half-life of mefenamic acid is approximately two hours. Half-lives ofmetabolites I and II have not been precisely reported, but appear to be longer than the parent compound.3 The metabolites may accumulate in patients with renal or hepatic failure. The mefenamic acid glucuronide may bind irreversibly to plasma proteins. Because both renal and hepatic excretion are significant pathways of elimination, dosage adjustments in patients with renal or hepatic dysfunction may be necessary. MEFENAMIC ACID should not be administered to patients with preexisting renal disease or in patients with significantly impaired renal function. TABLE 1. Pharmacokinetic Parameter Estimates for Mefenamic Acid

PK Parameters Normal Healthy Adults (18-45 yr)
Value CV
Tmax (hr) 2 66
Oral Clearance (L/hr) 21.23 38
Apparent volume of distribution; Vz/F (L/kg) 1.06 60
Half-life; t ½ (hrs) 2 to 4 NA

Special Populations

Pediatric: MEFENAMIC ACID has not been adequately investigated in pediatric patients less than 14 years of age. A study in 17 preterm infants administered 2 mg/kg indicated that the half life was about five times as long as adults, consistent with the low activity of metabolic enzymes in newborn infants. The mean Cmax in this study was 4 mcg/mL (range 2.9-6.1). The mean time to maximum concentration (Tmax ) was 8 hours (range 2-18 hrs).11 Race: Pharmacokinetic differences due to race have not been identified. Hepatic Insufficiency: Mefenamic acid pharmacokinetics have not been studied in patients with hepatic dysfunction. As hepatic metabolism is a significant pathway of mefenamic acid elimination, patients with acute and chronic hepatic disease may require reduced doses of MEFENAMIC ACID compared to patients with normal hepatic function. Renal Insufficiency: Mefenamic acid pharmacokinetics have not been investigated in subjects with renal insufficiency. Given that mefenamic acid, its metabolites and conjugates are primarily excreted by the kidneys, the potential exists for mefenamic acid metabolites to accumulate. MEFENAMIC ACID should not be administered to patients with preexisting renal disease or in patients with significantly impaired renal function.

Clinical Studies

In controlled, double-blind, clinical trials, MEFENAMIC ACID was evaluated for the treatment of primary spasmodic dysmenorrhea. The parameters used in determining efficacy included pain assessment by both patient and investigator; the need for concurrent analgesic medication; and evaluation of change in frequency and severity of symptoms characteristic of spasmodic dysmenorrhea. Patients received either Ponstel, 500 mg (2 capsules) as an initial dose of 250 mg every 6 hours, or placebo at onset of bleeding or of pain, whichever began first. After three menstrual cycles, patients were crossed over to the alternate treatment for an additional three cycles. Ponstel was significantly superior to placebo in all parameters, and both treatments (drug and placebo) were equally tolerated.

Mefenamic-Acid Indications and Usage

Carefully consider the potential benefits and risks of MEFENAMIC ACID and other treatment options before deciding to use MEFENAMIC ACID. Use the lowest effective dose for the shortest duration consistent with individual patient treatment goals (see WARNINGS). MEFENAMIC ACID is indicated:

  • For relief of mild to moderate pain in patients ≥ 14 years of age, when therapy will not exceed one week (7 days).
  • For treatment of primary dysmenorrhea.

CONTRAINDICATIONS

MEFENAMIC ACID is contraindicated in patients with known hypersensitivity to mefenamic acid. MEFENAMIC ACID should not be given to patients who have experienced asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs. Severe, rarely fatal, anaphylactic-like reactions to NSAIDs have been reported in such patients (see WARNINGS — Anaphylactoid Reactions, and PRECAUTIONS — Preexisting Asthma). MEFENAMIC ACID is contraindicated for the treatment of peri-operative pain in the setting of coronary artery bypass graft (CABG) surgery (see WARNINGS). MEFENAMIC ACID is contraindicated in patients with acute active ulceration or chronic inflammation of either the upper or lower gastrointestinal tract. MEFENAMIC ACID should not be used in patients with preexisting renal disease.

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