CAPTOPRIL

CAPTOPRIL
(kap'toe-pril)
Capoten
Classifications: angiotensin-converting enzyme (ace) inhibitor; antihypertensive agent;
Therapeutic: antihypertensive agent
; ace inhibitor
Prototype: Enalapril
Pregnancy Category: C first trimester; D second and third trimester

Availability

12.5 mg, 25 mg, 50 mg, 100 mg tablets

Action

Lowers blood pressure by specific inhibition of the angiotensin-converting enzyme (ACE). This interrupts conversion sequences initiated by renin that lead to formation of angiotensin II, a potent vasoconstrictor. ACE inhibition alters hemodynamics without compensatory reflex tachycardia or changes in cardiac output (except in patients with CHF). Peripheral vascular resistance is lowered by vasodilation. Inhibition of ACE also leads to decreased circulating aldosterone. In heart failure, captopril administration is followed by a fall in CVP and pulmonary wedge pressure; hypotensive action appears to be unrelated to plasma renin levels.

Therapeutic Effect

Effective in stepped protocol management of hypertension to convert to normotensive range, and in congestive heart failure with resulting decreases in dyspnea and improved exercise tolerance.

Uses

Hypertension; CHF (with digitalis and diuretics), diabetic nephropathy, left ventricular dysfunction post MI.

Unlabeled Uses

Idiopathic edema.

Contraindications

Angioedema, hypersensitivity to captopril or ACE inhibitors; hypotension; pregnancy (catetory C first trimester and category D second and third trimester), lactation.

Cautious Use

Impaired renal function, patient with solitary kidney; collagen-vascular diseases (scleroderma, SLE); patients receiving IMMUNOSUPPRESSANTS or other drugs that cause leukopenia or agranulocytosis; autoimmune disease, bone marrow suppression, coronary or cerebrovascular disease; cardiomyopathy, aortic stenosis; severe salt/volume depletion; heart failure, renal artery stenosis, renal disease, renal failure, renal impairment; hyperkalemia, elderly.

Route & Dosage

Hypertension
Adult: PO 6.25–25 mg t.i.d., may increase to 50 mg t.i.d. (max: 450 mg/d)
Child: PO 0.3–12.5 mg/kg q12–24h, may titrate up to max of 6 mg/kg/d in 2–4 divided doses
Infant: PO 0.15–0.3 mg/kg, may titrate up to 6 mg/kg/d in 1–4 divided doses
Neonate: PO 0.05–0.1 mg/kg q8–24h, may titrate up to 0.5 mg/kg q6–24h
Premature infant: PO 0.01 mg/kg q8–12h

Congestive Heart Failure
Adult: PO 6.25–12.5 mg t.i.d., may increase to 100 mg t.i.d. (max: 450 mg/d)

Renal Insufficiency
Clcr 10–50 mL/min: 75% of dose; <10 mL/min: 50% of dose

Administration

Oral
  • Give captopril 1 h before meals. Food reduces absorption by 30–40%.
  • Store in light-resistant containers at no more than 30° C (86° F) unless otherwise directed.

Adverse Effects (≥1%)

Body as a Whole: Hypersensitivity reactions, serum sickness-like reaction, arthralgia, skin eruptions. CV: Slight increase in heart rate, first dose hypotension, dizziness, fainting. GI: Altered taste sensation (loss of taste perception, persistent salt or metallic taste); weight loss, intestinal angioedema. Hematologic: Hyperkalemia, neutropenia, agranulocytosis (rare). Respiratory: Cough. Skin: Maculopapular rash, urticaria, pruritus, angioedema, photosensitivity. Urogenital: Azotemia, impaired renal function, nephrotic syndrome, membranous glomerulonephritis. Other: Positive antinuclear antibody (ANA) titers.

Diagnostic Test Interference

Elevated urine protein levels may persist even after captopril has been discontinued. Possibility of transient elevations of BUN and serum creatinine, slight increase in serum potassium, and serum prolactin, increases in liver enzymes, and false-positive urine acetone (using sodium nitroprusside reagent). Captopril may decrease fasting blood sugar in the nondiabetic and cause hypoglycemia in the diabetic patient controlled with antidiabetic drug therapy.

Interactions

Drug: nitrates, diuretics, and antihypertensives enhance hypotensive effects. Aspirin and other nsaids may antagonize hypotensive effects. potassium-sparing diuretics (spironolactone, amiloride) increase potassium levels. Probenecid decreases elimination and increases effects. Food: Food decreases absorption; take 30–60 min before meals.

Pharmacokinetics

Absorption: 60–75% absorbed; food may decrease absorption 25–40%. Onset: 15 min. Peak: 1–2 h. Duration: 6–12 h. Distribution: To all tissues except CNS; crosses placenta. Metabolism: Some liver metabolism. Elimination: Primarily in urine; excreted in breast milk.

Nursing Implications

Assessment & Drug Effects

  • Monitor BP closely following the first dose. A sudden exaggerated hypotensive response may occur within 1–3 h of first dose, especially in those with high BP or on a diuretic and restricted salt intake.
  • Advise bed rest and BP monitoring for the first 3 h after the initial dose.
  • Monitor therapeutic effectiveness. At least 2 wk of therapy may be required before full therapeutic effects are achieved.
  • Lab tests: Establish baseline urinary protein levels before initiation of therapy and check at monthly intervals for the first 8 mo of treatment and then periodically thereafter. Perform WBC and differential counts before therapy is begun and at approximately 2-wk intervals for the first 3 mo of therapy and then periodically thereafter.

Patient & Family Education

  • Report to physician without delay the onset of unexplained fever, unusual fatigue, sore mouth or throat, easy bruising or bleeding (pathognomonic of agranulocytosis).
  • Mild skin eruptions are most likely to appear during the first 4 wk of therapy and may be accompanied by fever and eosinophilia.
  • Consult physician promptly if vomiting or diarrhea occur.
  • Report darkening or crumbling of nailbeds (reversible with dosage reduction).
  • Taste impairment occurs in 5–10% of patients and generally reverses in 2–3 mo even with continued therapy.
  • Use OTC medications only with approval of the physician. Inform surgeon or dentist that captopril is being taken. Alert diabetic patient that captopril may produce hypoglycemia. Monitor blood glucose and HbA1c closely during first few weeks of therapy.

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

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