Captopril
1-[(2S)-3-mercapto-2-methylpropionyl]-L-proline (SQ-14225)
Also known as: Capoten · Capozide · captoprilum · SQ-14225
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| CHF / Hypertension | 0.5-2 mg/kg PO three times daily | PO | TID | — | 🌎 NA |
| CHF / Hypertension | 0.5-2 mg/kg PO q8-12h | PO | q8-12h | — | 🌎 NA |
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| CHF / Hypertension | 1/4 to 1/2 of a 12.5 mg tablet PO q8-12h | PO | q8-12h | — | 🌎 NA |
| Dilative, restrictive or hypertrophic cardiomyopathy | 0.55-1.54 mg/kg PO q8-12h | PO | q8-12h | — | 🌎 NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Captopril is a first-generation, sulfhydryl-containing Angiotensin-Converting Enzyme (ACE) inhibitor. Originally related to a peptide isolated from the venom of the South American pit viper (Bothrops jararaca), it holds historical significance as the first available ACE inhibitor.
While effective as a vasodilator for the treatment of congestive heart failure (CHF) and hypertension, its use in veterinary medicine has been largely supplanted by newer agents like enalapril and benazepril. This shift is primarily due to captopril's shorter half-life (often requiring TID dosing) and a higher incidence of adverse effects, particularly gastrointestinal upset in dogs.
Clinical Pearl: Unlike enalapril, captopril is an active drug and does not require hepatic biotransformation to an active metabolite to exert its effects.
Mechanism of action
Captopril acts as a competitive inhibitor of angiotensin-converting enzyme (ACE), for which it has a much higher affinity than the natural substrate, angiotensin-I.
- Angiotensin I → (blocked by ACE) → Angiotensin II (a potent vasoconstrictor).
- The reduction in Angiotensin II leads to vasodilation, decreasing total peripheral resistance, pulmonary vascular resistance, and blood pressure.
- Decreased Angiotensin II also reduces aldosterone secretion, leading to decreased sodium and water retention, while increasing plasma renin activity.
- Cardiovascular benefits in CHF include increased cardiac output, stroke volume, and exercise tolerance with little to no change in heart rate.
Safety & warnings
Contraindications
- Hypersensitivity to ACE inhibitors
Adverse effects
- Hypotension
- Renal failure
- Hyperkalemia
- Vomiting
- Diarrhea
- Skin rashes (reported in humans, not dogs)
- Neutropenia/agranulocytosis (rare, reported in humans)
Precautions
Use with caution and under close supervision in patients with renal insufficiency; doses may need to be reduced.
Use cautiously in patients with hyponatremia or sodium depletion, coronary or cerebrovascular insufficiency, preexisting hematologic abnormalities, or collagen vascular diseases (e.g., SLE).
Patients with severe CHF should be monitored very closely upon initiation of therapy to prevent profound hypotension.
Reproductive Safety: Captopril crosses the placenta. High doses in rodents caused decreased fetal weights and increased mortality. Use during pregnancy only when potential benefits outweigh risks (FDA Category C for 1st trimester; Category D for 2nd/3rd trimesters). Enters milk at ~1% of maternal plasma concentrations.
Drug interactions
Reduced oral absorption of captopril; separate dosing by at least two hours.
Concomitant use has caused neurologic dysfunction in human patients.
Digoxin levels may increase 15-30%; monitor serum digoxin levels.
Concomitant use may cause hypotension; titrate dosages carefully.
May reduce the clinical efficacy of captopril when used as an antihypertensive agent.
Increased risk of developing hyperkalemia.
Can decrease renal excretion of captopril, possibly enhancing clinical and toxic effects.
Concomitant use may cause additive hypotension; titrate dosages carefully.
Monitoring
- Clinical signs of CHF (respiratory rate/effort, exercise tolerance)
- Blood pressure (especially if treating hypertension or if signs of hypotension arise)
- Serum electrolytes (monitor for hyperkalemia)
- Renal panel (Creatinine, BUN)
- Urine protein
- CBC with differential (periodic)
Pharmacokinetics
Half-life
Absorption
In dogs, ~75% of an oral dose is absorbed, but food in the GI tract reduces bioavailability by 30-40%.
Distribution
Distributed to most tissues (excluding the CNS). Approximately 40% bound to plasma proteins in dogs. Crosses the placenta and enters milk.
Metabolism
Metabolized in the liver.
Elimination
More than 95% of a dose is excreted renally, both as unchanged drug (45-50%) and as metabolites. Half-life is significantly prolonged in patients with renal dysfunction.
Overdose
The primary concern in an overdose situation is hypotension.
- Treatment: Supportive treatment with volume expansion using normal saline is recommended to correct blood pressure.
- Toxicity thresholds: Dogs given 1.5 g/kg orally developed emesis and decreased blood pressure. Dogs receiving doses greater than 6.6 mg/kg q8h may develop renal failure.
Available products
Formulations
- Oral Tablets
- Oral Suspension (compounded)
Human-labeled
- Captopril Oral Tablets: 12.5 mg, 25 mg, 50 mg, & 100 mg (Capoten®, generic)
- Captopril and Hydrochlorothiazide Oral Tablets: 15mg/25mg, 15mg/50mg, 25mg/25mg, 25mg/50mg (Capozide®, generic)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store tablets in tight containers at temperatures not greater than 30°C. Compounded oral suspension (0.75 mg/mL in Ora-Plus/Ora-Sweet) retains >90% potency for 14 days at 5°C and 7 days at 25°C; protect from light.
Client information
Important: Give this medication on an empty stomach (1 hour before or 2 hours after meals) unless otherwise instructed, as food significantly decreases its absorption.
- Do not abruptly stop or reduce therapy without your veterinarian's approval.
- Contact your veterinarian immediately if your pet experiences severe or persistent vomiting or diarrhea, as this can lead to dangerous dehydration and low blood pressure.
- Monitor for signs of lethargy, weakness, or deterioration in your pet's condition, which could indicate low blood pressure or worsening heart disease.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.