Action

Inhibits electrolyte reabsorption from ascending loop of Henle and decreases reabsorption of sodium and potassium in distal renal tubules, increasing plasma osmotic pressure and promoting diuresis

Availability

Tablets: 2.5 mg, 5 mg, 10 mg

Indications and dosages

➣ Hypertension

Adult: 2.5 to 5 mg P.O. daily.

➣ Edema caused by heart failure or renal disease

Adults: 5 to 20 mg P.O. daily

Contraindications

• Hypersensitivity to drug

• Hepatic coma or precoma

• Anuria

Precautions

Use cautiously in:

• severe hepatic or renal impairment, gout, hyperparathyroidism, glucose tolerance abnormalities, fluid or electrolyte imbalances, bipolar disorders

• elderly patients

• pregnant or breastfeeding patients

• children (safety not established).

Administration

• Give in morning to avoid frequent nighttime urination.

• Discontinue drug before parathyroid function tests are performed.

• Be aware that metolazone is the only thiazide-like diuretic that may cause diuresis in patients with glomerular filtration rates below 20 ml/minute.

Adverse reactions

CNS: drowsiness, lethargy, vertigo, paresthesia, weakness, headache, fatigue

CV: chest pain, hypotension, palpitations, venous thrombosis, arrhythmias

GI: nausea, vomiting, bloating, cramping, anorexia, pancreatitis

GU: polyuria, nocturia, erectile dysfunction, decreased libido

Hematologic: aplastic anemia, leukopenia, agranulocytosis

Hepatic: hepatitis

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

Musculoskeletal: muscle cramps

Skin: photosensitivity, rashes

Other: chills

Interactions

Drug-drug. Amphotericin B, corticosteroids, mezlocillin, piperacillin, ticarcillin: additive hypokalemia

Antigout drugs: increased uric acid level

Antihypertensives, nitrates: additive hypotension

Digoxin: increased risk of digoxin toxicity

Lithium: decreased lithium excretion, increased risk of lithium toxicity

Drug-diagnostic tests. Bilirubin, calcium, cholesterol, creatinine, low-density lipoproteins, triglycerides, uric acid: increased levels

Blood glucose, urine glucose: increased levels in diabetic patients

Magnesium, potassium, protein-bound iodine, sodium, urinary calcium: decreased levels

Drug-food. Any food: increased metolazone absorption

Drug-herbs. Aloe, cascara sagrada, senna: increased risk of hypokalemia

Drug-behaviors. Sun exposure: increased risk of photosensitivity

Patient monitoring

• Monitor baseline and periodic electrolyte, blood urea nitrogen, glucose, and uric acid levels.

• Evaluate blood pressure regularly.

See Watch for signs and symptoms of hypokalemia, which may necessitate potassium supplements, potassium-rich diet, or potassium-sparing diuretic. Hypokalemia is particularly dangerous to patients who are on digitalis or have had ventricular arrhythmias.

• Assess patient for fluid and electrolyte imbalances.

Patient teaching

• Advise patient to take in morning to avoid frequent nighttime urination.

• Tell patient he may take with food or milk to prevent GI upset.

See Instruct patient to report muscle pain, weakness, or cramps; nausea; vomiting; diarrhea; dizziness; restlessness; excessive thirst; fatigue; drowsiness; increased pulse; or irregular heart beats.

• Inform patient that drug may cause gout attacks. Advise him to report sudden joint pain.

• Instruct patient to use sunscreen and protective clothing to avoid photosensitivity.

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