Mefenamic acid, also known by the trade name Ponstan, is a non-steroidal anti-inflammatory drug (NSAID), which has analgesic and anti-inflammatory properties.
Although mefenamic acid has an inflammatory and analgesic effect of mild to moderate intensity, it appears to be especially effective in the treatment of menstrual cramps.
In this article, we will provide the following information about mefenamic acid:
- What is it for?
- Most common trade names.
- Side effects.
- Drug interactions.
Warning: this text is not intended to reproduce the complete package insert for mefenamic acid. What we will do is a critical review of the drug in a language more accessible to the lay public, eliminating the parts of the more technical language and highlighting the information that is really relevant to patients who wish to take the product.
If you are looking for general information about all drugs in the class of NSAIDs, read: ANTI-INFLAMMATORY - Action and Side Effects.
What is meant by mefenamic acid
Mefenamic acid is usually indicated for:
- Treatment of pain in patients with rheumatoid arthritis.
- Treatment of pain in patients with osteoarthrosis.
- Mild to moderate pain, including headache, muscular, traumatic, dental, post-operative and postpartum.
- Primary dysmenorrhea (menstrual cramps).
- Menorrhagia (intense menstrual flow).
- Post-menstrual tension.
Among all of the above conditions, primary dysmenorrhoea is the most common cause of mefenamic acid prescription.
Why does mefenamic acid appear to be the best option for menstrual cramps?
Throughout the first phase of the menstrual cycle, the endometrium - the inner wall of the uterus - becomes more and more thick and vascularized, in order to be able to receive an embryo if the woman is fertilized after ovulation. However, if the ovum is not fertilized, the levels of hormones that stimulate endometrial proliferation in the The first stage of the cycle falls a lot, and this thick uterine wall literally collapses, characterizing the menstruation.
For all this devitalized tissue to be expelled, the uterus needs to contract frequently, which is why women experience cramps during menstruation. This uterine contraction is caused by chemical mediators called prostaglandins.
In some women, prostaglandins act exaggeratedly, causing such intense contractions, that even the uterine blood vessels are compressed, causing a temporary ischemia of the uterus. Women who have heavy menstrual cramps usually have high levels of prostaglandin in menstrual fluid.
While most anti-inflammatories act to inhibit the production of prostaglandins, mefenamic acid also acts on the prostaglandins already produced. Because of this extra effect, although all anti-inflammatories are effective in treating menstrual cramps, mefenamic acid seems to be the one with the best results.
Mefenamic acid can be found in its generic form or through the various commercial names available in the market, among which we highlight:
The only presentation available in the Brazilian market, whether generic or branded, is that of 500 mg tablets. In Portugal, mefenamic acid is sold only under the brand name Ponstan with 250 mg tablets.
Average price of mefenamic acid
In Brazil, the box of generic medicine with 24 500 mg tablets costs around 7 reais. The box of 24 tablets of 500 mg of Ponstan costs between 14 and 30 reais.
In Portugal, the Ponstan of 250 mg costs around, 0 euros the box with 20 tablets and, 0 euros the box with 60 tablets.
How to take
There are two correct forms of administration of mefenamic acid:
- 1 tablet of 500 mg of 8/8 hours for 3 to 5 days.
- 1 initial 500 mg tablet followed by 250 mg every 6 hours for 3 to 5 days.
Due to the risk of side effects, it is recommended that the medication is not used for more than 7 days in a row.
The tablet may be given with meals, but it should not be broken, crushed or chewed.
The most common adverse effects of mefenamic acid are:
- Fluid retention.
- Arterial hypertension.
- Acute renal failure with elevated blood creatinine.
- Hyperkalemia (elevation of blood potassium).
- Abdominal cramps.
- Dyspepsia (burning of the stomach).
- Duodenal or gastric ulcer (at risk of bleeding or perforation).
- Increased liver enzymes (TGO and TGP).
As a non-steroidal anti-inflammatory drug, mefenamic acid shares the class, with the most relevant being the risk of peptic ulcer, acute renal injury and increased risk of events cardiovascular diseases. The longer the use of NSAIDs, the greater the chance of these complications.
To minimize the risk of serious side effects, it is suggested to use the drug for only 3 to 5 consecutive days, and to avoid its use in people over 65 years.
Contraindications and precautions
Mefenamic acid should not be administered to any patient who has ever had an allergic reaction or bronchospasm-related crisis with any NSAID or acetylsalicylic acid.
As anti-inflammatories inhibit the action of platelets, in patients with scheduled surgery, the medication must be at least 48 hours prior to the procedure to reduce the risk of bleeding in the intra and postoperative.
Mefenamic acid should also be avoided in patients with the following conditions:
- Cardiac insufficiency.
- Elevated risk of cardiovascular diseases.
- Past gastritis or peptic ulcer.
- History of gastrointestinal bleeding.
- Renal insufficiency.
- Advanced liver disease, such as cirrhosis.
- Poorly controlled arterial hypertension.
- Active bleeding.
- Thrombocytopenia (very low platelet blood level).
- Hyperkalemia (high levels of potassium in the blood).
Any non-steroidal anti-inflammatory drugs can impair female fertility and should therefore also be avoided in women who are trying to conceive.
Drug Interactions of Mefenamic Acid
The combination of mefenamic acid with other medicinal products may cause the following adverse drug interaction effects:
- Any other NSAIDs- high risk of gastrointestinal and renal damage.
- Alcohol- high risk of gastrointestinal adverse effects and liver toxicity.
- Anticoagulants (heparin and warfarin)- increased risk of bleeding.
- Inhibitors of platelet aggregation (ex.ticlopidine and clopidogrel)- increased risk of bleeding.
- Lithium- risk of increased lithium levels in the blood.
- Methotrexate- increased risk of haematological toxicity.
- Colchicine- increases the risk of gastrointestinal ulceration or bleeding.
- Corticosteroids (ex. prednisone, prednisolone, dexamethasone)- increased risk of ulceration or gastrointestinal bleeding.
- Diuretics (ex. furosemide, hydrochlorothiazide, chlorthalidone)- reduction of diuretic effectiveness and increased risk of developing acute renal failure.
- Spironolactone- increased risk of hyperkalemia (increased potassium in the blood) and acute kidney injury.
- ACE inhibitors (ex. ramipril, enalapril, lisinopril) or angiotensin II antagonists (ex. irbesartan, losartan, valsartan)- increased risk of hyperkalemia (increased potassium in the blood) and acute kidney injury.
- Tenofovir- increases the risk of acute kidney injury.
- Antihypertensive drugs- risk of reduction of the antihypertensive effect.
- Ciclosporin or tacrolimus- increases the risk of acute kidney injury and hypertension.
- Selective serotonin reuptake inhibitors (ex. fluoxetine, paroxetine, sertraline)- increased risk of gastrointestinal bleeding.
- Ginkgo biloba- increased risk of bleeding.
- Insulin or oral hypoglycemic agents- increased risk of hypoglycaemia.
Alert your doctor if you are taking any of the drugs listed above.