methazolamide

Therapeutic Classification: diuretics

Pharmacologic Classification: carbonic anhydrase inhibitors

Indications ⬆ ⬇

REMS

Lowering of intraocular pressure in the treatment of glaucoma.

Action ⬆ ⬇

Inhibition of carbonic anhydrase in the eye results in decreased secretion of aqueous humor.
Inhibit renal carbonic anhydrase, resulting in self-limiting urinary excretion of sodium, potassium, bicarbonate, and water.

Therapeutic effects:

Lowering of intraocular pressure.

Pharmacokinetics ⬆ ⬇

Absorption: Well absorbed after oral administration.

Distribution: Crosses the placenta.

Metabolism/Excretion: 15–30% excreted unchanged in urine.

Half-Life: 14 hr.

Time/Action Profile ⬆ ⬇

(↓ intraocular pressure)

ROUTE	ONSET	PEAK	DURATION
PO	2–4 hr	6–8 hr	10–18 hr

Contraind./Precautions ⬆ ⬇

Contraindicated in:

Hypersensitivity or cross-sensitivity with sulfonamides may occur ;
Concurrent use of oral and ophthalmic carbonic anhydrase inhibitors is not recommended;
OB: Avoid during first trimester of pregnancy.

Use Cautiously in:

Chronic respiratory disease;
Electrolyte abnormalities;
Renal or hepatic impairment;
Diabetes mellitus;
OB: Second or third trimester of pregnancy or lactation (safety not established).

Adv. Reactions/Side Effects ⬆ ⬇

Derm: rash

EENT: transient nearsightedness

Endo: hyperglycemia

F and E: hyperchloremic acidosis, hypokalemia

GI: anorexia, metallic taste, nausea, vomiting

GU: crystalluria, renal calculi

Hemat: APLASTIC ANEMIA, HEMOLYTIC ANEMIA, LEUKOPENIA

Metab: weight loss, hyperuricemia

Neuro: depression, fatigue, paresthesias, weakness, drowsiness

Misc: allergic reactions

Interactions ⬆ ⬇

Drug-drug:

May ↑ excretion of barbiturates, aspirin, and lithium and lead to ↓ effectiveness.
May ↓ excretion of amphetamines,quinidine,procainamide, cyclosporine, and possibly tricyclic antidepressants and lead to toxicity.

Route/Dosage ⬆ ⬇

PO (Adults ): 50–100 mg 2–3 times daily.

Availability ⬆ ⬇

(Generic available)

Tablets: 25 mg; 50 mg

Assessment ⬆ ⬇

Assess for eye discomfort or decrease in visual acuity.
Observe patient for signs of hypokalemia (muscle weakness, malaise, fatigue, ECG changes, vomiting).
- Assess for allergy to sulfonamides.

Lab Test Considerations:

Evaluate serum electrolytes, CBC, and platelet counts initially and periodically during prolonged therapy. May cause ↓ potassium, bicarbonate, WBC, and RBC. May cause ↑ serum chloride.
- May cause ↑ in serum and urine glucose; monitor serum and urine glucose carefully in patients with diabetes.
- May cause false-positive results for urine protein and 17-hydroxysteroid tests.
- May cause ↑ blood ammonia, bilirubin, uric acid, urine urobilinogen, and calcium. May ↓ urine citrate.

Implementation ⬆ ⬇

Do not confuse methazolamide with methimazole or metolazone.
Encourage fluids to 2000–3000 mL/day, unless contraindicated, to prevent crystalluria and stone formation.
- A potassium supplement without chloride should be administered concurrently with carbonic anhydrase inhibitors.
PO: Give with food to minimize GI irritation. Tablets may be crushed and mixed with fruit-flavored syrup to minimize bitter taste for patients with difficulty swallowing.

Patient/Family Teaching ⬆ ⬇

Instruct patient to take as directed. Take missed doses as soon as possible unless almost time for next dose. Do not double doses.
Advise patient of the need for periodic ophthalmologic exams; loss of vision may be gradual and painless.
Advise patient to report numbness or tingling of extremities, weakness, rash, sore throat, unusual bleeding or bruising, or fever to health care professional. If hematopoietic reactions, fever, rash, or renal problems occur, carbonic anhydrase inhibitor therapy should be discontinued.
May occasionally cause drowsiness. Caution patient to avoid driving and other activities that require alertness until response to the drug is known.
Caution patient to use sunscreen and wear protective clothing to prevent photosensitivity reactions.

Evaluation/Desired Outcomes ⬆ ⬇

Decrease in intraocular pressure when used for glaucoma. If therapy is not effective or patient is unable to tolerate one carbonic anhydrase inhibitor, using another may be effective and more tolerable.

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Pronunciation ⬇

Classifications ⬆ ⬇