Methazolamide
Pronunciation: meth-ah-ZOLE-ah-mide
Class: Carbonic anhydrase inhibitor
Trade Names
Methazolamide
- Tablets 25 mg
- Tablets 50 mg
Pharmacology
Inhibits carbonic anhydrase enzyme, reducing rate of aqueous humor secretion and, thus, lowering IOP.
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
AdultsPO 50 to 100 mg twice daily or 3 times daily.
Drug Interactions
Aspirin (high-dose)Anorexia, tachypnea, lethargy, coma, and death have been reported.
SteroidsUse 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.
More Methazolamide resources
- Methazolamide Monograph (AHFS DI)
- Methazolamide Prescribing Information (FDA)
- methazolamide Concise Consumer Information (Cerner Multum)
- methazolamide MedFacts Consumer Leaflet (Wolters Kluwer)
- Neptazane Prescribing Information (FDA)
