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Methenamide: Full Drug Profile

Medically reviewed by Min Clinic Staff | Updated: January 2026

Methenamide - General Information

A carbonic anhydrase inhibitor that is used as a diuretic and in the treatment of glaucoma. [PubChem]

 

Pharmacology of Methenamide

Methenamide is topical carbonic anhydrase inhibitor. Methenamide is indicated for the reduction of elevated intraocular pressure in patients with open-angle glaucoma or ocular hypertension who are insufficiently responsive to beta-blockers. Methenamide is a sulfonamide derivative; however, it does not have any clinically significant antimicrobial properties. Although methazolamide achieves a high concentration in the cerebrospinal fluid, it is not-considered an effective anticonvulsant. Methenamide has a weak and transient diuretic effect, therefore use results in an increase in urinary volume, with excretion of sodium, potassium and chloride.

 

Methenamide for patients

Adverse reactions common to all sulfonamide derivatives may occur: anaphylaxis, fever, rash (including erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis), crystalluria, renal calculus, bone marrow depression, thrombocytopenic purpura, hemolytic anemia, leukopenia, pancytopenia and agranulocytosis. Precaution is advised for early detection of such reactions and the drug should be discontinued and appropriate therapy instituted.

Caution is advised for patients receiving high-dose aspirin and methazolamide concomitantly.

 

Methenamide Interactions

Methazolamide should be used with caution in patients on steroid therapy because of the potential for developing hypokalemia.

Caution is advised for patients receiving high-dose aspirin and methazolamide concomitantly, as anorexia, tachypnea, lethargy, coma and death have been reported with concomitant use of high-dose aspirin and carbonic anhydrase inhibitors.

 

Methenamide Contraindications

Methazolamide therapy is contraindicated in situations in which sodium and/or potassium serum levels are depressed, in cases of marked kidney or liver disease or dysfunction, in adrenal gland failure, and in hyperchloremic acidosis. In patients with cirrhosis, use may precipitate the development of hepatic encephalopathy.

Long-term administration of methazolamide is contraindicated in patients with angle-closure glaucoma, since organic closure of the angle may occur in spite of lowered intraocular pressure.

 

Additional information about Methenamide

Methenamide Indication

For treatment of chronic open-angle glaucoma and acute angle-closure glaucoma

Mechanism Of Action
Methenamide is a potent inhibitor of carbonic anhydrase. Inhibition of carbonic anhydrase in the ciliary processes of the eye decreases aqueous humor secretion, presumably by slowing the formation of bicarbonate ions with subsequent reduction in sodium and fluid transport.
Drug Interactions
Aspirin The salicylate at high dose increases the effect of the carbonic anhydrase inhibitors
Generic Name
Methazolamide
Drug Category
Diuretics; Carbonic Anhydrase Inhibitors
Drug Type
Small Molecule; Approved
Other Brand Names containing Methazolamide
MZM; Methenamide; Naptazane; Neptazane; Neptazaneat;
Absorption
Methazolamide is well absorbed from the gastrointestinal tract.
Toxicity (Overdose)
Electrolyte imbalance, development of an acidotic state, and central nervous system effects might be expected to occur in the case of an overdose.
Protein Binding
55%
Half Life
14 hours
Dosage Forms of Methenamide
Tablet Oral
Chemical IUPAC Name
N-(3-methyl-5-sulfamoyl-1,3,4-thiadiazol-2-ylidene)acetamide
Chemical Formula
C5H8N4O3S2
Organisms Affected
Humans and other mammals