Captopril is an angiotensin-converting enzyme (ACE) inhibitor used in the treatment of hypertension and heart failure. It was developed in the 1970s through structure-based drug design inspired by snake venom peptides. Captopril was the first orally active ACE inhibitor introduced into clinical practice. Its development marked a major breakthrough in cardiovascular pharmacotherapy. The drug works by blocking the conversion of angiotensin I to angiotensin II, reducing blood pressure. It was approved for medical use in the early 1980s. Captopril significantly improved outcomes in patients with heart disease. Its success led to the development of newer ACE inhibitors. It was later included in major pharmacopeias worldwide. Today, captopril remains an important reference drug in cardiovascular treatment.
BRAND NAMES
Captopril is available globally under various brand names, including Capoten (most recognized), Acepril, Captoril, Captopril Sandoz, and Kaplon. All contain the same active ingredient and are used for identical medical purposes.
MECHANISM OF ACTION
ACE exists in two isoforms: somatic ACE, a 1277-amino acid glycoprotein with two functional domains (N and C), and testicular ACE, which is smaller and involved in sperm maturation. The C-domain primarily regulates blood pressure, while the N-domain influences hematopoietic stem cells. ACE inhibitors, including captopril, block both domains but show higher affinity for the C-domain. Captopril, a non-prodrug, competes with angiotensin I (ATI), preventing its conversion to angiotensin II (ATII), lowering blood pressure, and increasing plasma renin activity. Its binding affinity for ACE is approximately 30,000 times higher than that of ATI.
PHARMACOKINETICS
Absorption: In fasting individuals, 60–75% of captopril is absorbed. Food may reduce absorption by 25–40%, though this is often not clinically significant.
Distribution: The drug has a volume of distribution of 0.8 L/kg, indicating limited tissue distribution and primarily extracellular presence.
Metabolism: Captopril is active without hepatic activation and is metabolized in both blood and liver. Its sulfhydryl (–SH) group undergoes oxidation to form reversible disulfide metabolites.
Excretion: Mainly excreted by the kidneys, mostly as unchanged drug with some metabolites. Renal elimination involves glomerular filtration and active tubular secretion, resulting in a short half-life.
PHARMACODYNAMICS
Captopril blocks the renin-angiotensin-aldosterone system (RAAS), a key regulator of blood pressure and fluid balance. Normally, renin converts angiotensinogen to ATI, which ACE then converts to ATII. ATII raises blood pressure by stimulating aldosterone and ADH release, promoting sodium and water retention, causing vasoconstriction, and triggering thirst. By preventing ATI conversion to ATII and inhibiting bradykinin breakdown, captopril lowers blood pressure and enhances vasodilation.
ADMINISTRATION
Captopril should be taken on an empty stomach at least one hour before meals to maximize absorption. It is usually administered two to three times daily, with the exact dose and schedule determined by a physician.
DOSAGE AND STRENGTH
Hypertension: Start with 25 mg two or three times daily, adjustable up to 450 mg/day.
Heart Failure: Begin with 6.25–12.5 mg three times daily, gradually increasing to maintenance dose.
Diabetic Nephropathy: Typically 25 mg three times daily.
DRUG INTERACTIONS
Captopril interacts with several medications affecting its efficacy and safety:
Diuretics: Enhance blood pressure reduction.
Potassium supplements/potassium-sparing diuretics: Risk of hyperkalemia.
NSAIDs: May reduce antihypertensive effect and increase kidney damage risk.
Other antihypertensives: Can cause excessive hypotension.
Lithium: Increased risk of toxicity.
Gold salts: May trigger nitritoid reactions (flushing, nausea, hypotension).
Other RAAS inhibitors (ARBs, aliskiren): Heightened risk of hyperkalemia, hypotension, and kidney injury.
FOOD INTERACTIONS
Captopril’s absorption decreases with food intake, and potassium-rich foods may increase the risk of hyperkalemia. It should be taken on an empty stomach for optimal effect.
CONTRAINDICATIONS
Captopril is contraindicated in individuals with a history of hypersensitivity to ACE inhibitors, pregnancy, or severe renal impairment.
SIDE EFFECTS
Dry, persistent cough
Dizziness or lightheadedness, particularly when standing
Altered or metallic taste
Headache
Fatigue or tiredness
Nausea, vomiting, or diarrhea
Skin rash or itching
OVERDOSE
Severe hypotension, dizziness, fainting, or shock
Hyperkalemia
Acute kidney injury
Tachycardia as a compensatory response
Management: Supportive care with IV fluids, electrolyte monitoring, and hemodialysis if necessary
TOXICITY
Captopril toxicity may occur from overdose or specific risk factors, leading to severe hypotension, electrolyte imbalances, acute kidney injury, or rarely life-threatening angioedema. Management includes supportive care, monitoring of blood pressure and electrolytes, and hemodialysis in severe cases.
