What is hydralazine?
Hydralazine (brand name Apresoline®) is a vasodilator drug. It is used off label (extra label) to treat high blood pressure and certain causes of heart failure in cats and dogs.
Many drugs are commonly prescribed for off-label use in veterinary medicine. “Off label” means the drug is being used in a way that has not been reviewed or approved by the U.S. Food and Drug Administration (FDA) or Health Canada. In these instances, follow your veterinarian’s directions and cautions carefully, as they may be significantly different from those on the label.
How is hydralazine given?
- Hydralazine is given by mouth in the form of a tablet or compounded liquid. It can also be given as an injection while your pet is in the hospital or clinic.
- Hydralazine should be given with food.
- This medication is usually given at a lower dose and gradually increased over time to the therapeutic dose.
- Measure liquid doses carefully.
This medication will take effect quickly, in about 1 to 2 hours, and improvement in clinical signs should follow.
What if I miss giving my pet the medication?
If you miss a dose, give it as soon as you remember, and then continue with the regular dosing schedule. If it is almost time for the next dose, skip the missed dose and resume the regular dosing schedule. Do not give the pet two doses at once.
Are there any potential side effects?
Hydralazine may cause side effects. Contact your veterinarian if these signs are severe, get worse, or persist:
- decreased appetite
- vomiting
- diarrhea
Serious adverse reactions may occur. If any of the following signs develop, stop giving hydralazine and contact your veterinarian immediately:
- weakness
- tiredness
- collapse
- swelling of the legs (water retention)
Other side effects may occur, based on human studies, including:
- a lupus-like syndrome
- increased tear production
- red/inflamed eyes
- blood abnormalities
- constipation
- urine retention
This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.
Are there any risk factors for this medication?
Hydralazine should NOT BE USED in pets with:
- allergies to hydralazine
- heart vessel disease
- low blood pressure
- severe dehydration
- severe blood loss
Hydralazine should be USED WITH CAUTION in pets that:
- have kidney disease,
- have brain bleeds
- have pre-existing autoimmune diseases
- are pregnant or lactating
Are there any drug interactions I should be aware of?
The following medications should be used with caution when given with hydralazine:
- angiotensin-converting enzyme (ACE) inhibitors
- beta-blockers
- diazoxide
- diuretics
- furosemide
- monoamine oxidase inhibitors (MAOIs)
- propranolol
- sympathomimetics
Certain medications may interact with hydralazine and so it is important to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your dog is taking before starting any new treatment.
Is there any monitoring needed with this medication?
- Before starting treatment, your veterinarian will take baseline chest X-rays so that changes may be monitored during therapy.
- Your veterinarian may monitor gum color, blood electrolyte levels, blood pressure, and blood cell counts while your pet is on this medication.
- Your veterinarian may monitor your pet to be sure that the medication is working.
How do I store hydralazine?
- Store hydralazine at room temperature.
- Protect from light.
- Store compounded forms of this medication according to the label.
What should I do in case of emergency?
If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.
