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Methazolamide (Monograph)

Drug class: Carbonic Anhydrase Inhibitors
ATC class: S01EC05
VA class: CV703
CAS number: 554-57-4

Medically reviewed by Drugs.com on May 15, 2023. Written by ASHP.

Introduction

Carbonic anhydrase inhibitor; nonbacteriostatic sulfonamide derivative.

Uses for Methazolamide

Glaucoma

Adjunctive treatment of open-angle glaucoma. Used principally in situations involving acute IOP elevation or chronically elevated IOP that is refractory to maximal topical ocular hypotensive therapy prior to a more definitive procedure to reduce IOP. Long-term use limited by systemic adverse effects.

Adjunctive treatment of secondary glaucoma.

Short-term use in acute angle-closure glaucoma to lower IOP before appropriate laser or incisional surgery. Should not be used for long-term treatment of angle-closure glaucoma. (See Contraindications under Cautions.)

Methazolamide Dosage and Administration

Administration

Administer orally.

Dosage

Adults

Glaucoma
Open-angle or Secondary Glaucoma, Acute Angle-closure Glaucoma
Oral

50–100 mg 2 or 3 times daily. Adjust dosage based on patient response and requirements.

Cautions for Methazolamide

Contraindications

Warnings/Precautions

Sensitivity Reactions

Sulfonamide Sensitivity Reactions

Serious adverse events (e.g., Stevens-Johnson syndrome, toxic epidermal necrolysis, fulminant hepatic necrosis, agranulocytosis, aplastic anemia, other blood dyscrasias) associated with sulfonamide therapy possible.

Discontinue if signs of hypersensitivity, blood dyscrasias, or other serious reactions occur.

General Precautions

Respiratory Effects

Caution in patients with pulmonary obstruction, emphysema, or advanced pulmonary disease where alveolar ventilation may be impaired. Methazolamide may precipitate or aggravate acidosis in these patients.

Laboratory Monitoring

Monitor for hematologic reactions associated with sulfonamides; obtain a CBC and platelet count before therapy and periodically during therapy. Discontinue the drug if clinically important changes occur.

Monitor serum electrolytes periodically.

Specific Populations

Pregnancy

Category C.

Lactation

Not known whether methazolamide is distributed into human milk. Discontinue nursing or drug.

Pediatric Use

Safety and efficacy not established.

Hepatic Impairment

Avoid use in patients with marked hepatic impairment, including those with cirrhosis, because of the risk of developing hepatic encephalopathy. (See Contraindications.)

Renal Impairment

Avoid use in patients with marked renal impairment. (See Contraindications.)

Common Adverse Effects

Paresthesia, hearing dysfunction or tinnitus, fatigue, malaise, anorexia, altered taste, nausea, vomiting, diarrhea, polyuria, drowsiness, confusion.

Drug Interactions

Specific Drugs and Laboratory Tests

Drug or Test

Interaction

Comments

Amphetamine

Decreased urinary excretion of amphetamines; potentiates the effects of amphetamines

Amphotericin B

Possible enhanced potassium depletion

Antidiabetic agents (oral agents, insulin)

May interfere with the hypoglycemic response

Aspirin

Increased risk of toxicity

Avoid concomitant use in patients receiving high-dose aspirin

Carbonic anhydrase inhibitors, topical

Additive systemic effects

Concomitant use not recommended

Corticosteroids

Possible enhanced potassium depletion

Digitalis glycosides

Methazolamide-induced hypokalemia may potentiate toxicity of digitalis

Lithium

Increased renal excretion of lithium

Monitor patient

Methenamine

May interfere with urinary antiseptic effect of methenamine

Quinidine

Decreased urinary excretion of quinidine

Tests for urinary protein

False-positive results with tests that use bromophenol blue reagent (Albustix) or sulfosalicylic acid

Methazolamide Pharmacokinetics

Absorption

Bioavailability

Well absorbed from the GI tract, with peak plasma concentrations usually attained within 1–2 hours.

Onset

Reduction in IOP occurs in 2–4 hours; peak effect occurs in 6–8 hours.

Duration

Reduction in IOP persists for 10–18 hours.

Distribution

Extent

Distributed into erythrocytes, extracellular fluid, bile, the aqueous humor of the eye, and CSF.

Crosses placenta in unknown quantities.

Not known whether methazolamide is distributed into human milk.

Plasma Protein Binding

55%.

Elimination

Metabolism

Partially metabolized in liver.

Elimination Route

About 20–30% of a dose is excreted in urine as active metabolites. Fate of the remainder of the dose not determined.

Half-life

14 hours.

Stability

Storage

Oral

Tablets

Tight container at 20–25°C.

Actions

Advice to Patients

Preparations

Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name

methazolAMIDE

Routes

Dosage Forms

Strengths

Brand Names

Manufacturer

Oral

Tablets

25 mg*

methazolAMIDE Tablets

50 mg*

methazolAMIDE Tablets

AHFS DI Essentials™. © Copyright 2024, Selected Revisions May 24, 2021. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, Maryland 20814.

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