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Captopril for dogs is an ACE inhibitor. This class of drugs prevents the body from releasing a chemical called angiotensin II, which constricts blood vessels and raises blood pressure in the body.

Though made for humans, many vets use captopril to control high blood pressure and treat congestive heart failure in cats and canines. Captopril is also used off-label to slow the progression of renal failure, treat coronary artery disease, and prevent heart attacks in dogs with a history of myocardial infarctions.

Dosage

The recommended dosage of captopril for dogs ranges from 0.25 mg to 1 mg per lb. Most vets recommend dogs take captopril 2 to 3 times a day. Dogs with low kidney function should take a lower dose since their body isn’t able to remove captopril as quickly as dogs with normal renal function.

Captopril comes in 12.5 mg, 25 mg, 50 mg, and 100 mg tablets. Vets sometimes direct caregivers to cut tablets in half or fourths depending on the pet's weight. Captopril can be tough to dose for small dogs since the smallest available dosage is 12.5 mg tablets. Because of this, some vets prefer to prescribe quinapril — a comparable drug that comes in 5 mg tablets.

Efficacy

A clinical study on 72 dogs with canine heart failure found that captopril was as effective at managing symptoms as other ACE inhibitors. However, it is shorter-acting than other ACE inhibitors and is administered more frequently.

Side effects

Here are some common side effects canines may experience when taking captopril: 

  • Poor appetite

  • Nausea 

  • Loose stools

  • "Hoarse" bark

  • Dry cough

  • Fatigue

  • Disorientation

Rarely, captopril for dogs can cause more severe side effects. Talk to your vet if your dog is experiencing any of the following: 

  • Dehydration

  • Hyperemesis

  • Prolonged diarrhea 

  • Decrease in urination

  • Muscle weakness

  • Rash

  • Renal damage

  • Elevated potassium levels

  • Swelling of the face or extremities

  • Fever

  • Trouble breathing

  • Intense scratching

  • Infections

  • Mouth sores

  • Inability to urinate

  • Changes in heart rhythm

  • Unexplainable weight gain

  • Chills

  • Opportunistic infections

Considerations

Talk to your vet about the risks and benefits of captopril before giving it to dogs with chronic kidney disease, low blood pressure, small vessel disease, electrolyte deficiencies, or persistent dehydration. Diabetic canines shouldn't take captopril with any medicines containing renin inhibitors such as Amturnide, Tekturna, Tekamlo, or Valturna. 

This medication is known to lower white blood cell counts in canines and humans. White blood cells, also called leukocytes, are the body's primary defense against germs. The suppressed immune response can make canines more susceptible to opportunistic infections while taking this medication. Use captopril with caution if your dog has a weak immune system or is on immunosuppressant therapy. 

Prescribing captopril for dogs during pregnancy is not recommended since studies show it can cause brain abnormalities, facial deformities, and fetal death.

Drug interactions

Captopril for dogs may interact with the following drugs:

  • Anesthetics

  • Antacids

  • Diuretics

  • Vasodilators

  • Oral glycerin

  • Gout medications (probenecid)

  • NSAID and opioid pain relievers

  • Heart and blood pressure medications (digoxin, sildenafil)

  • Muscle relaxants (baclofen)

  • Anti-anxiety medications (buspirone, doxepin)

  • Tricyclic antidepressants (doxepin)

  • Antihistamines (cimeditine, diphenhydramine)

  • Corticosteroids

  • Potassium supplements

  • Anemia medications (darbepoetin alfa)

Please note this is not a complete list. Let your vet know if your dog is taking other prescription or over-the-counter medications.

Allergic reactions and sensitivity

Captopril shouldn't be used for dogs that are allergic to benazepril, elanapril, lisinopril, or other ACE inhibitors. Serious and sometimes deadly reactions can occur.

Seek medical care immediately if you believe your pet is having an allergic reaction to captopril. Signs of an ACE inhibitor reaction include:

  • Rash

  • Itching

  • Stomach cramps

  • Swelling of the mouth, face, throat, or extremities.

  • Trouble breathing

Frequently asked questions

How long does a dose of captopril last for dogs?

For dogs with normal kidney function, captopril's effects last about a day. Captopril lasts longer in dogs with poor renal function because their body has to work harder to remove the drug from their system. 

Will my dog need to be monitored while taking captopril?

Your vet will conduct several tests while your dog is taking captopril, including blood, urine, and kidney tests. Additional tests, such as X-rays, may be required for dogs diagnosed with congestive heart failure.

My pet just started this medicine last week. How long does it take captopril for dogs to take effect?

Captopril starts working almost immediately, but it can take weeks to see an effect on blood pressure levels. Most dogs will have a marked decrease in blood pressure after about a month on this medication.

My dog is drinking a lot of water since starting captopril. Should I limit their water intake?

No. Captopril's effects can make dogs develop dehydration very quickly. Allow your dog to drink as much water as they want. Talk to your vet if you suspect there might be other contributing factors at play.

Can my dog take captopril with food? 

Don’t give captopril with meals since food can interfere with absorption. Studies show that captopril’s bioavailability is cut in half when taken on a full stomach. It’s best to wait at least 30 minutes after administering captopril before feeding your dog.

Can I store captopril in my bathroom medicine cabinet?

Moisture, heat, and UV rays can all decrease the effectiveness of captopril. Keep this medicine in a cool, dark, and dry place that's out of reach of children and pets.

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