METHAZOLAMIDE
(meth-a-zoe'la-mide)
Neptazane
Classifications: eye preparation; carbonic anhydrase inhibitor; sulfonamide derivative; anti-glaucoma
Prototype: Acetazolamide
Pregnancy Category: C

Availability

25 mg, 50 mg tablets

Actions

Nonbactericidal sulfonamide derivative similar to acetazolamide but with slower onset and longer duration of action. Appears to cause more drowsiness and fatigue than acetazolamide does, and has less diuretic activity.

Therapeutic Effects

Inhibits carbonic anhydrase activity in eye by reduces rate of aqueous humor formation with consequent lowering of intraocular pressure.

Uses

Adjunctive treatment in chronic simple (open-angle) glaucoma and secondary glaucoma and preoperatively in acute angle-closure glaucoma when delay of surgery is desired in order to lower intraocular pressure. May be used concomitantly with miotic and osmotic agents.

Contraindications

Glaucoma due to severe peripheral anterior synechiae, severe or absolute glaucoma, hemorrhagic glaucoma; hypokalemia, hyponatremia.

Cautious Use

Pregnancy (category C), lactation.

Route & Dosage

Glaucoma
Adult: PO 50–100 mg b.i.d. or t.i.d.

Administration

Oral

Give with meals to minimize GI distress.

Adverse Effects (1%)

Body as a Whole: Malaise, drowsiness, fatigue, lethargy. GI: Mild GI disturbance, anorexia. CNS: Headache, vertigo, paresthesias, mental confusion, depression.

Interactions

Drug: Renal excretion of amphetamines, ephedrine, flecainide, quinidine, procainamide, tricyclic antidepressants may be decreased, thereby enhancing or prolonging their effects; increases renal excretion of lithium; excretion of phenobarbital may be increased; amphotericin B, corticosteroids may add to potassium loss; hypokalemia caused by methazolamide may predispose patients on digitalis glycosides to digitalis toxicity; patients on high doses of salicylates are at higher risk for salicylate toxicity.

Pharmacokinetics

Absorption: Slowly absorbed from GI tract. Onset: 2–4 h. Peak: 6–8 h. Duration: 10–18 h. Distribution: Distributed throughout body, concentrating in RBCs, plasma, and kidneys; crosses placenta. Metabolism: Partially metabolized in liver. Elimination: Excreted primarily in urine.

Nursing Implications

Assessment & Drug Effects

Supervise ambulation in older adult, since drug may cause vertigo.
Assess patient's ability to perform ADL since drug may cause fatigue and lethargy.
Lab tests: Obtain periodic serum electrolytes, especially in older adults. Monitor lithium levels with concurrent administration of lithium and methazolamide.

Patient & Family Education

Be aware that drug may cause drowsiness. Advise caution with hazardous activities until response to drug is known.
Do not breast feed while taking this drug without consulting physician.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug