Ponstel (Mefenamic Acid) - Drug Interactions, Contraindications, Overdosage, etc

DRUG INTERACTIONS

ACE-inhibitors

Reports suggest that NSAIDs may diminish the antihypertensive effect of ACE inhibitors.  This interaction should be given consideration in patients taking NSAIDs concomitantly with ACE-inhibitors.

Aspirin

When PONSTEL is administered with aspirin, its protein binding is reduced, although the clearance of free PONSTEL is not altered.  The clinical significance of this interaction is not known; however, as with other NSAIDs, concomitant administration of MEFENAMIC ACID and aspirin is not generally recommended because of the potential of increased adverse reactions.

Diuretics

Clinical studies, as well as post marketing observations, have shown that PONSTEL can reduce the natriuretic effect-of furosemide and thiazides in some patients.  This response has been attributed to inhibition of renal prostaglandin synthesis.  During concomitant therapy of NSAIDs, the patient should be observed closely for signs of renal failure (see PRECAUTIONS, Renal Effects), as well as to assure diuretic efficacy.

Lithium

NSAIDs have produced an elevation of plasma lithium levels and a reduction in renal lithium clearance.  The mean minimum lithium concentration increased 15% and the renal clearance decreased by approximately 20%.  These effects have been attributed to inhibition of renal prostaglandin synthesis by the NSAID.  Thus, when NSAIDs and lithium are administered concurrently, subjects should be observed carefully for signs of lithium toxicity.

Methotrexate

NSAIDs have been reported to competitively inhibit methotrexate accumulation in rabbit kidney slices.  This may indicate that they could enhance the toxicity of methotrexate.  Caution should be used when NSAIDs are administered concomitantly with methotrexate.

Warfarin

The effects of warfarin and NSAIDs on GI bleeding are synergistic, such that users of both drugs together have a risk of serious GI bleeding higher than users of either drug alone.

Antacids

In a single dose study (n=6), ingestion of an antacid containing 1.7-gram of magnesium hydroxide with 500-mg of mefenamic acid increased the Cmax and AUC of mefenamic acid by 125% and 36%, respectively.¹

OVERDOSAGE

Symptoms following acute NSAIDs overdoses are usually limited to lethargy, drowsiness, nausea, vomiting, and epigastric pain, which are generally reversible with supportive care. Gastrointestinal bleeding can occur. Hypertension, acute renal failure, respiratory depression and coma may occur, but are rare. Anaphylactoid reactions have been reported with therapeutic ingestion of NSAIDs, and may occur following an overdose.
 
 
Patients should be managed by symptomatic and supportive care following an NSAID
overdose. There are no specific antidotes. Emesis and/or activated charcoal (60 to 100 g in adults, 1 to 2 g/kg in children) and/or osmotic cathartic may be indicated in patients seen within 4 hours of ingestion with symptoms or following a large overdose (5 to 10 times the usual dose). Forced diuresis, alkalinization of urine, hemodialysis, or hemoperfusion may not be useful due to high protein binding.

CONTRAINDICATIONS

PONSTEL is contraindicated in patients with known hypersensitivity to Mefenamic acid. 
 
PONSTEL 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).
 
PONSTEL is contraindicated for the treatment of peri-operative pain in the setting of coronary artery bypass graft (CABG) surgery (see WARNINGS).
 
Ponstel is contraindicated in patients with active ulceration or chronic inflammation of either the upper or lower gastrointestinal tract.
 
Ponstel should not be used in patients with preexisting renal disease.