METHYCLOTHIAZIDE

METHYCLOTHIAZIDE (meth-i-kloe-thye'a-zide) Duretic , Enduron Classifications: thiazide diuretic; antihypertensive agent; Therapeutic: antihypertensive; thiazide diuretic Prototype: Hydrochlorothiazide Pregnancy Category: D first trimester; C second and third trimester

Availability

2.5 mg, 5 mg tablets

Action

Thiazide diuretic similar to hydrochlorothiazide. Diuretic effect results from a drug-induced inhibition of the renal tubular reabsorption of electrolytes. The excretion of sodium and chloride is enhanced. There is also a loss of potassium ions via the kidney. BP is lowered, probably by the loss of sodium, chloride and water, and, consequently, blood volume. Edema is also decreased in CHF patients by the same mechanism.

Therapeutic Effect

Antihypertensive effect as well as enhanced excretion of sodium and water.

Uses

Antihypertensive treatment and adjunctively in the management of edema associated with CHF, renal pathology, and hepatic cirrhosis.

Contraindications

Hypersensitivity to thiazides, and sulfonamide derivatives; anuria, hypokalemia, pregnancy (category D) in first trimester and pregnancy (category C second and third trimester), lactation.

Cautious Use

Renal disease; impaired kidney or liver function; older adults; gout; SLE; hypercalcemia; diabetes mellitus, children.

Route & Dosage

Edema Adult: PO 2.5–10 mg once/d or 3–5 times/wk Hypertension Adult: PO 2.5–10 mg/d Child: PO 0.05–0.2 mg/kg/d

Administration

Oral

• Give early in a.m. after eating (reduces gastric irritation) to prevent sleep interruption because of diuresis. If 2 doses are ordered, administer second dose no later than 3 p.m.
• Store at 15°–30° C (59°–86° F) unless otherwise instructed.

Adverse Effects (≥1%)

Body as a Whole: Postural hypotension, sialadenitis, unusual fatigue, dizziness, paresthesias. Skin: Photosensitivity. Special Senses: Yellow vision. Metabolic: Hypokalemia. Hematologic: Agranulocytosis.

Interactions

Drug: Amphotericin B, corticosteroids increase hypokalemic effects; may antagonize hypoglycemic effects of insulin, sulfonylureas; cholestyramine, colestipol decrease thiazide absorption; intensifies hypoglycemic and hypotensive effects of diazoxide; increased potassium and magnesium loss may cause digoxin toxicity; decreases lithium excretion, increasing its toxicity; nsaids may attenuate diuresis, and risk of nsaid-induced kidney failure increased.

Pharmacokinetics

Absorption: Incompletely absorbed. Onset: 2 h. Peak: 6 h. Duration: >24 h. Distribution: Distributed throughout extracellular tissue; concentrates in kidney; crosses placenta; distributed in breast milk. Metabolism: Does not appear to be metabolized. Elimination: In urine.

Nursing Implications

Assessment & Drug Effects

• Expect antihypertensive effects in 3–4 d; maximal effects may require 3–4 wk.
• Monitor BP and I&O ratio during first phase of antihypertensive therapy. Report a sudden fall in BP, which may initiate severe postural hypotension and potentially dangerous perfusion problems, especially in the extremities.
• Lab tests: Periodic serum electrolytes and CBC with differential.
• Monitor patient for S&S of hypokalemia (see Appendix F). Report promptly. Physician may change dose and institute replacement therapy.

Patient & Family Education

• Eat a balanced diet to protect against hypokalemia; generally not severe even with long-term therapy. Prevent onset by eating potassium-rich foods including a banana (about 370 mg potassium) and at least 180 mL (6 oz) orange juice (about 330 mg potassium) every day.
• Watch carefully for loss of glycemic control (diabetics) and early signs of hyperglycemia (see Appendix F). Symptoms are slow to develop.
• Avoid OTC drugs unless the physician approves them. Many preparations contain both potassium and sodium, and may induce electrolyte imbalance adverse effects.
• Older adults are more responsive to excessive diuresis; orthostatic hypotension may be a problem.
• Change positions slowly and in stages from lying down to upright positions; avoid hot baths or showers, extended exposure to sunlight, and standing still. Accept assistance as necessary to prevent falling.
• Do not drive or engage in potentially hazardous activities until adjustment to the hypotensive effects of drug has been made.

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