ATC Class:S01EC05

VA Class:CV703

AHFS Class:

• Carbonic Anhydrase Inhibitors 52:40.12

Generic Name(s):

• methazolAMIDE

Methazolamide is a carbonic anhydrase inhibitor.

Methazolamide is used only in the adjunctive treatment of open-angle (noncongestive, chronic simple) or secondary glaucoma and for short-term preoperative therapy in angle-closure (obstructive, narrow-angle) glaucoma when delay of surgery is desired in order to lower intraocular pressure (IOP). Long-term use of oral carbonic anhydrase inhibitors is limited by systemic adverse effects.134,136 (See Uses: Glaucoma, in the Carbonic Anhydrase Inhibitors General Statement 52:40.12.)

Administration

Methazolamide is administered orally.

Dosage

Dosage of methazolamide must be adjusted according to the patient's requirements and response. The usual adult dosage of methazolamide is 50-100 mg 2 or 3 times daily.

Methazolamide shares the pharmacologic actions and toxic potentials of the carbonic anhydrase inhibitors, and the usual precautions of carbonic anhydrase inhibitor therapy should be observed. (See Cautions in the Carbonic Anhydrase Inhibitors General Statement 52:40.12.) The manufacturers state that long-term use of methazolamide is contraindicated in patients with angle-closure glaucoma since further closure of the angle may occur despite a reduction in intraocular pressure (IOP).150

Pharmacokinetics

Absorption

Methazolamide is absorbed more slowly from the GI tract and disappears more slowly from the plasma than does acetazolamide.

Distribution

Methazolamide is distributed into plasma, erythrocytes, extracellular fluid, bile, the aqueous humor of the eye, and CSF. The drug crosses the placenta in unknown quantities. It is not known whether methazolamide is distributed into the milk of nursing women.

Elimination

Methazolamide is partially metabolized in the liver. About 20-30% of a dose is excreted in urine as substances with carbonic anhydrase inhibitor activity. The fate of the remainder of the dose has not been determined.

Chemistry and Stability

Chemistry

Methazolamide is a carbonic anhydrase inhibitor. Methazolamide occurs as a white or slightly yellow crystalline powder. The drug is very slightly soluble in water and in alcohol and has a pK_a of 7.3.

Stability

Methazolamide tablets should be stored in tight containers at 20-25°C.150 Commercially available methazolamide tablets have an expiration date of 5 years following the date of manufacture.

Additional Information

For further information on chemistry, pharmacology, pharmacokinetics, uses, cautions, drug interactions, laboratory test interferences, and dosage and administration of methazolamide, see the Carbonic Anhydrase Inhibitors General Statement 52:40.12.

Only references cited for selected revisions after 1984 are available electronically.

134. Inoue K. Managing adverse effects of glaucoma medications. Clin Ophthalmol . 2014; 8:903-13. [PubMed 24872675]

135. Prum BE Jr, Herndon LW, Moroi SE et al. Primary open angle closure preferred practice pattern^® guideline. San Francisco, CA: American Academy of Ophthalmology; 2015. From the American Academy of Ophthalmology website. [Web]

136. Canadian Ophthalmological Society Glaucoma Clinical Practice Guideline Expert Committee, Canadian Ophthalmological Society. Canadian Ophthalmological Society evidence-based clinical practice guidelines for the management of glaucoma in the adult eye. Can J Ophthalmol . 2009; 44 Suppl 1:S7-93. [PubMed 19492005]

137. Jackson J, Carr LW III, Fisch BM et al. Care of the patient with primary angle closure glaucoma. St. Louis, MO: American Optometric Association; Reviewed 2001. From American Optometric Association website. [Web]

150. Effcon Laboratories. Methazolamide tablet prescribing information. Marietta, GA; 2017 Jul.