Mefenamic Acid

Introduction

Mefenamic acid is an anti-steroidal antiinflammatory drug, an NSAID. It is used in musculoskeletal and joint disorders such as alkylosing spondylitis, osteoarthritis and rheumatoid arthritis including juvenile idiopathic arthritis. It is also used in mensrual pain, headache, dental pain, postoperative and postpartum pain.

Generic Name 藥名	HA Code 藥物代碼	Classification藥物分類
Mefenamic Acid Capsule 250 mg		P1S1S3

Mechanism of Action

Non-opioid Analgesic (NSAID) Anti-inflammatory agent, Nonselective COX inhibitor, inhibits COX-1 and COX-2

Dosage

In the treatment of rheumatic disorders:

Oral: 500 mg three times daily.

It is recommended that it should not be given for longer than 7 days at a time.

Administration in children

Oral dose in those over 6 months of age: 25mg/kg daily in divided doses.

Side Effects

As for NSAIDs in general.

Naproxen suppositories can cause rectal irritation and occasional bleeding.

Naproxen should be used with caution in renal impairment, and use is not recommended in patients whose creatinine clearance is less than 20 mL/min.

Common side effects include heartburn, nausea, dyspepsia, diarrhoea, constipation, gastrointestinal ulceration/bleeding, headache, dizziness, rash, salt and fluid retention, and high blood pressure.

Note: Naproxen poses an intermediate risk of stomach ulcers compared with ibuprofen, which is low-risk, and indomethacin which is high-risk.

Effects on the blood: localized spontaneous bleeding, bruising and prolonged bleeding time have been reported.

It also increases the risk of heart attack, stroke, kidney failure and liver failure.

NSAID can also worsen asthma.

Naproxen may cause muscle cramps in the legs in 3% of people.

Cardiovascular risk

Chronic ibuprofen use has been found correlated with risk of progression to hypertension and myocardial infarction (heart attack). Both the U.S. Food and Drug Administration (FDA) and The European Medicines Agency (EMA) issues warnings of increased heart attack and stroke risk.

Skin

NSAIDs has been associated with the onset of bullous pemphigoid. It can also cause serious skin adverse events such as exfoliative dermatitis, Stevens-Johnson syndrome, and toxic epidermal necrolysis which can be fatal.

Pharmacokinetics

Mefenamic acid is absorbed from the gastrointestinal tract. Peak plasma concentrations occur about 2 to 4 hours after ingestion.

At therapeutic concentrations it is more than 90% bound to plasma proteins.

Small amounts are distributed into breast milk.

Mefenamic acid is metabolized by the cytochrome P450 isoenzyme CYP2C9. The plasma elimination half-life is about 2 to 4 hours.

Mefenamic acid and its metabolites are excreted via the urine (52-67%) and the faeces.

Drug Management

Efficiency:

• Pain and inflammation control

Safety:

• monitor signs of bleeding and bruising, and blood pressure.

Drug Interaction:

• Increases the blood thinning effects of warfarin because it displaces them from their plasma protein binding and increases their free concentrations in the bloodstream.
• Increase the risk of adverse effects of lithium, methotrexate and cardiac glycosides by lowering their excretion via the kidneys.
• Risk of nephrotoxicity may be increased if given with ACE inhibitors, ciclosporin, tacrolimus or diuretics
• Combination with antihypertensive drugs such as ACE inhibitors, sartans and diuretics can decrease their effectiveness as well as increase the risk for kidney toxicity.
• Antihypertensive effects of ACEIs, beta blockers and diuretics may be reduced
• Use of more than one NSAID together (including aspirin) should be avoided because of the increased risk of adverse effects.
• It adds to the risk of gastrointestinal bleeding and ulceration when used with steroids, the SSRIs, the SNRI venlafaxaine, the antiplatelet clopidogrel, bisphosphonates or pentoxifylline.

Co-adminstration of ACE inhibitor can increase risk of kidney problem and increase hypotensive effect. Aspirin.

Precaution:

• There has been a report of a patient with Parkinson’s disease whose symptoms had previously been well controlled but who deteriorated when she was given naproxen.

Caution:

• Allergic reaction,
• Previous peptic ucler
• uncontrolled hypertension,
• Impaired renal function

Contraindication:

• Hypersensitivity against mefenamic acid
• History of allergic reactions (bronchospasm, rhinitis, urticaria) following the use of other NSAIDs such as aspirin
• Third-trimester pregnancy
• Active stomach and/or duodenal ulceration or gastrointestinal bleeding
• Inflammatory bowel disease such as Crohn’s disease or ulcerative colitis
• Severe congestive heart failure (NYHA III/IV)
• Severe liver insufficiency
• Severe chronic kidney disease (creatinine clearance <30 mi/min)
• Caution in patients with pre-existing hepatic porphyria, as diclofenac may trigger attacks
• Caution in patients with severe, active bleeding such as cerebral hemorrhage
• Caution in patients with fluid retention or heart failure
• Can lead to onset of new hypertension or worsening of pre-existing hypertension

FAQ

How should I take the tablet?

Follow the doctor's prescription Take with food if diclofenac upsets your stomach.

What should I avoid while taking?

Avoid alcohol consumption.

What happen if I overdose?

Contact your primary care doctor. If emergency situation, call 999

What happen if I miss a dose?

Take it as soon as you remember. If it is near the time of the next dose, skip the missed dose. Take your next dose at the regular time. Do not double the dose to catch up.