Microzide

Action

Increases sodium and water excretion by inhibiting sodium reabsorption in distal tubules; promotes excretion of chloride, potassium, magnesium, and bicarbonate. Also may produce arteriolar dilation, reducing blood pressure.

Availability

Capsules: 12.5 mg

Oral solution: 10 mg/ml, 100 mg/ml

Tablets: 12.5 mg, 25 mg, 50 mg, 100 mg

Indications and dosages

➣ Edema caused by heart failure, renal dysfunction, cirrhosis, corticosteroid therapy, or estrogen therapy

Adults: 25 to 100 mg P.O. daily as a single dose or in divided doses. Maximum dosage is 200 mg/day.

➣ Mild to moderate hypertension

Adults: Initially, 12.5 mg daily P.O.; then, based on blood pressure response, may give 12.5 to 50 mg/day P.O. Higher dosages may be given in refractory cases.

Children ages 2 to 12: 1 to 2 mg/kg/day P.O. in single dose or two divided doses, not to exceed 100 mg/day

Children younger than age 2: 1 to 2 mg/kg P.O. as single dose or divided doses, not to exceed 37.5 mg/day; infants less than age 6 months may require dosage of 3 mg/kg/day in two divided doses.

Off-label uses

• Hypercalcemia

• Ménière's disease

Contraindications

• Hypersensitivity to drug, other thiazides, sulfonamides, or tartrazine

• Renal decompensation or anuria

Precautions

Use cautiously in:

• renal or severe hepatic impairment, fluid or electrolyte imbalances, gout, systemic lupus erythematosus, hyperparathyroidism, glucose tolerance abnormalities, bipolar disorder

• elderly patients

• pregnant or breastfeeding patients.

Administration

• Give with food or milk if GI upset occurs.

• Administer early in day so diuretic effect doesn't disturb sleep.

Adverse reactions

CNS: dizziness, drowsiness, lethargy, headache, insomnia, nervousness, vertigo, asthenia, asterixis, paresthesias, confusion, fatigue, encephalopathy

CV: chest pain, orthostatic hypotension, ECG changes, thrombophlebitis, arrhythmias

EENT: nystagmus

GI: nausea, vomiting, epigastric distress, anorexia, pancreatitis

GU: polyuria, nocturia, erectile dysfunction, loss of libido, renal failure

Hematologic: anemia, hemolytic anemia, agranulocytosis, leukopenia, thrombocytopenia

Hepatic: jaundice, hepatitis

Metabolic: dehydration, gout, hyperglycemia, hypokalemia, hypocalcemia, hypovolemia, hypomagnesemia, hyponatremia, hypophosphatemia, hyperuricemia, hypochloremic alkalosis

Musculoskeletal: muscle cramps

Skin: photosensitivity, urticaria, rash, dermatitis, purpura, alopecia, flushing

Other: fever, weight loss, anaphylaxis

Interactions

Drug-drug. Adrenocorticotropic hormone, corticosteroids: increased risk of intensified electrolyte depletion, particularly hypokalemia

Allopurinol: increased risk of hypersensitivity reaction

Amphotericin B, corticosteroids, digoxin, mezlocillin, piperacillin, ticarcillin: increased risk of hypokalemia

Antihypertensives, barbiturates, nitrates, opioids: increased hypotension

Cholestyramine, colestipol: decreased hydrochlorothiazide absorption

Digoxin: increased risk of hypokalemia

Insulin, oral hypoglycemics: possible decreased hypoglycemic effect

Lithium: decreased excretion and increased blood level of lithium

Nondepolarizing skeletal muscle relaxants (such as tubocurarine): increased skeletal muscle relaxant effect

Nonsteroidal anti-inflammatory drugs: decreased hydrochlorothiazide efficacy

Vasopressors: decreased pressor effect

Drug-diagnostic tests. Bilirubin, blood and urine glucose (in diabetic patients), calcium, creatinine, uric acid: increased levels

Cholesterol, low-density lipoproteins, magnesium, potassium, protein-bound iodine, sodium, triglycerides, urinary calcium: decreased levels

Drug-herbs. Dandelion: interference with diuretic activity

Ginkgo: decreased antihypertensive effect

Licorice, stimulant laxative herbs (aloe, cascara sagrada, senna): increased risk of hypokalemia

Drug-behaviors. Alcohol use: increased hypotension

Sun exposure: increased risk of photo-sensitivity

Patient monitoring

• Monitor blood pressure, fluid intake and output, and daily weight.

• Assess electrolyte levels, especially potassium. Monitor for signs and symptoms of hypokalemia.

• Monitor blood urea nitrogen and creatinine levels.

• Check blood glucose level in diabetic patients.

• Assess for signs and symptoms of gout attacks in patients with gouty arthritis.

Patient teaching

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

• Tell patient to take early in day to avoid nighttime urination.

• Instruct patient to track intermittent doses on calendar.

• Tell patient to weigh himself daily, at same time on same scale and wearing same clothes.

☞ Instruct patient to report decreased urination, swelling, unusual bleeding or bruising, dizziness, fatigue, numbness, and muscle weakness or cramping.

• Instruct patient to move slowly when sitting up or standing, to avoid dizziness from sudden blood pressure decrease.

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

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