diamox

Action

Inhibits carbonic anhydrase in kidney, decreasing water reabsorption and increasing excretion of sodium, potassium, and bicarbonate. Lowers intraocular pressure by decreasing aqueous humor production. May raise seizure threshold by reducing carbonic anhydrase in CNS, thereby decreasing neuronal conduction.

Availability

Capsules (sustained-release): 500 mg

Injection: 500 mg/vial

Tablets: 125 mg, 250 mg

Indications and dosages

➣ Open-angle (chronic simple) glaucoma (given with miotics)

Adults: 250 mg P.O. one to four times daily, or 500-mg sustained-release capsule P.O. once or twice daily. Don't exceed total daily dosage of 1 g.

➣ Preoperative treatment of closed-angle (secondary) glaucoma

Adults: 250 mg P.O. q 4 hours or 250 mg P.O. b.i.d.; in acute cases only, 500 mg P.O. followed by 125 to 250 mg P.O. q 4 hours. For rapid relief of increased intraocular pressure, 500 mg I.V., repeated in 2 to 4 hours; then 125 to 250 mg P.O. q 4 to 6 hours.

Children: 10 to 15 mg/kg/day P.O. in divided doses q 6 to 8 hours, or 5 to 10 mg/kg I.V. q 6 hours

➣ Seizure disorder (given with other anticonvulsants)

Adults and children: 250 mg P.O. daily when given with another anticonvulsant, or 8 to 30 mg/kg daily P.O. in one to four divided doses. Usual dosage range is 375 mg to 1 g daily.

➣ Drug-induced edema or edema secondary to heart failure

Adults: Initially, 250 to 375 mg P.O. daily. If diuresis fails, give dose on alternate days, or give for 2 days alternating with day of rest.

Children: 5 mg/kg P.O. daily, or 150 mg/m² P.O. or I.V. once daily in morning

➣ Acute high-altitude (mountain) sickness

Adults: 500 mg to 1 g P.O. daily in divided doses, or sustained-release capsule q 12 to 24 hours. Dosing should begin 24 to 48 hours before ascent and continue during ascent and for 48 hours after reaching desired altitude. For rapid ascent, 1-g P.O. dose is recommended.

Dosage adjustment

• Mild renal failure

Off-label uses

• Acute pancreatitis

• Alkalosis after open-heart surgery

• Hereditary ataxia

• Peptic ulcer

• Periodic paralysis

• Renal calculi

• Phenobarbital or lithium overdose

• Hydrocephalus in infants

Contraindications

• Hypersensitivity to drug or sulfonamides

• Adrenocortical insufficiency

• Closed-angle glaucoma

• Severe pulmonary obstruction

• Severe renal disease, hypokalemia, hyponatremia

• Hepatic disease

Precautions

Use cautiously in:

• respiratory, renal, or hepatic disease; diabetes mellitus, hypercalcemia, gout, adrenocortical insufficiency

• pregnant or breastfeeding patients.

Administration

☞ Before giving, ask if patient is pregnant. Drug may cause fetal toxicity.

• Direct I.V. administration is preferred. When giving by direct I.V. route, reconstitute 500-mg vial with more than 5 ml of sterile water for injection; administer over 1 minute.

• When giving drug intermittently by I.V. infusion, further dilute with normal saline solution or dextrose solution and infuse over 4 to 8 hours.

• Be aware that I.M. administration is painful because solution is alkaline.

• If necessary, crush tablets and mix in nonsweet, nonalcoholic syrup or non-glycerin solution.

Adverse reactions

CNS: weakness, nervousness, irritability, drowsiness, confusion, dizziness, depression, tremor, headache, paresthesia, flaccid paralysis, seizures

EENT: transient myopia, tinnitus, hearing dysfunction, sensation of lump in throat

GI: nausea, vomiting, diarrhea, constipation, melena, abdominal distention, dry mouth, anorexia

GU: dysuria, hematuria, glycosuria, polyuria, crystalluria, renal colic, renal calculi, uremia, sulfonamide-like renal lesions, renal failure

Hematologic: thrombocytopenia, leukopenia, agranulocytosis, hemolytic anemia, thrombocytopenic purpura, pancytopenia, bone marrow depression with aplastic anemia

Hepatic: hepatic insufficiency

Metabolic: hypokalemia, hyperglycemia and glycosuria, hyperuricemia and gout, metabolic acidosis, hyperchloremic acidosis

Respiratory: hyperpnea

Skin: rash, pruritus, urticaria, photosensitivity, hirsutism, cyanosis

Other: altered taste and smell, weight loss, fever, excessive thirst, pain at I.M. injection site, hypersensitivity reaction, Stevens-Johnson syndrome

Interactions

Drug-drug. Amphetamines, procainamide, quinidine, tricyclic antidepressants: decreased excretion and enhanced or prolonged effect of these drugs, leading to toxicity

Amphotericin B, corticosteroids, corticotrophin, other diuretics: increased risk of hypokalemia

Lithium, phenobarbital, salicylates: increased excretion of these drugs, possibly reducing their efficacy

Methenamine compounds: inactivation of these drugs

Phenytoin, primidone: severe osteomalacia

Salicylates: increased risk of salicylate toxicity

Drug-diagnostic tests. Ammonia, bilirubin, calcium, chloride, glucose, uric acid: increased levels

Thyroid iodine uptake: decreased in patients with hyperthyroidism or normal thyroid function

Urinary protein (with some reagents): false-positive result

Drug-behaviors. Sun exposure: increased risk of photosensitivity

Patient monitoring

☞ Evaluate for signs and symptoms of sulfonamide sensitivity; drug can cause fatal hypersensitivity.

☞ Monitor laboratory test results for hematologic changes; blood glucose, potassium, bicarbonate, and chloride levels; and liver and kidney function changes.

• Observe for signs and symptoms of bleeding tendency.

• Monitor fluid intake and output.

Patient teaching

• Advise patient to take drug with food if GI upset occurs.

• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.

• Tell patient to eat potassium-rich foods (such as seafood, bananas, and oranges) if taking drug long term or receiving other potassium-depleting drugs.

• Advise patient to avoid activities that can cause injury. Advise him to use soft toothbrush and electric razor to avoid gum and skin injury.

• Tell patient to report significant numbness or tingling.

• Inform patient that he'll undergo regular blood testing during therapy.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, and behaviors mentioned above.