Methazolamide

Pronunciation: meth-ah-ZOLE-ah-mide
Class: Carbonic anhydrase inhibitor

Trade Names

Methazolamide
- Tablets 25 mg
- Tablets 50 mg

Apo-Methazolamide (Canada)

Pharmacology

Inhibits carbonic anhydrase enzyme, reducing rate of aqueous humor secretion and, thus, lowering IOP.

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Pharmacokinetics

Absorption

Well absorbed from the GI tract, reaching peak plasma levels in 1 to 2 h. The C max for the 25, 50, and 100 mg twice daily dosing regiments are 2.5, 5.1, and 10.7 mcg/mL, respectively. The AUCs are 1,130, 2,571, and 5,418 mcg•min/mL, respectively.

Distribution

Methazolamide is distributed throughout the body including plasma, cerebrospinal fluid, aqueous humor, RBC, bile, and extracellular fluid. The Vd ranges from 17 to 23 L. Approximately 55% is bound to plasma proteins.

Elimination

Mean steady-state plasma elimination t ½ is about 14 h. Approximately 25% is recovered unchanged in the urine over the dosing interval and renal Cl accounts for 20% to 25% of the total Cl.

Onset

Decrease in IOP usually occurs in 2 to 4 h.

Peak

About 6 to 8 h.

Duration

About 10 to 18 h.

Indications and Usage

Treatment of ocular conditions where lowering IOP is likely to be of therapeutic benefit (eg, chronic open-angle glaucoma, secondary glaucoma, preoperatively in acute angle-closure glaucoma).

Contraindications

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 (may precipitate hepatic encephalopathy); long-term administration in patients with angle-closure glaucoma.

Dosage and Administration

Adults

PO 50 to 100 mg twice daily or 3 times daily.

Drug Interactions

Aspirin (high-dose)

Anorexia, tachypnea, lethargy, coma, and death have been reported.

Steroids

Use with caution because of risk of developing hypokalemia.

Laboratory Test Interactions

None well documented.

Adverse Reactions

CNS

Paresthesias; malaise; drowsiness; confusion; loss of appetite; convulsions.

Dermatologic

Urticaria; Stevens-Johnson syndrome; toxic epidermal necrolysis.

EENT

Hearing dysfunction; tinnitus; transient myopia.

Electrolytes

Electrolyte imbalance.

GI

Taste alteration; GI disturbance (including nausea, vomiting, diarrhea); melena.

Genitourinary

Polyuria; hematuria; glucosuria; crystalluria; renal calculi.

Hematologic

Agranulocytosis; aplastic anemia; other blood dyscrasias.

Hepatic

Hepatic insufficiency; fulminant hepatic necrosis.

Metabolic

Metabolic acidosis.

Musculoskeletal

Flaccid paralysis.

Miscellaneous

Photosensitivity.

Precautions

Pregnancy

Category C .

Lactation

Undetermined.

Children

Safety and efficacy not established.

Hypersensitivity

Patients with known sulfonamide sensitivity may show allergic reactions to methazolamide.

Hepatic Function

Use could precipitate hepatic coma.

Pulmonary conditions

Use in pulmonary obstruction and emphysema may aggravate or precipitate acidosis.

Copyright © 2009 Wolters Kluwer Health.

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