By Rania Gollakner, BS, DVM, MPH

What is hydralazine?

Hydralazine (brand name: Apresoline®) is a vasodilator drug used to treat high blood pressure and certain causes of heart failure.

Its use in cats and dogs to treat hypotension and certain causes of heart failure is ‘off label’ or ‘extra label’. Many drugs are commonly prescribed for off label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully as their directions 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, and should be given with food. It can also be given in the form of an injection while your pet is in the hospital or clinic setting. 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 when you remember, but if it is close to the time for the next dose, skip the dose you missed and give it at the next scheduled time, and return to the regular dosing schedule. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

Side effects may include decreased appetite, vomiting or diarrhea, and are usually not serious unless they are severe, get worse, or persist. Serious side effects include weakness, tiredness, collapse, or swelling of the legs (water retention). Other side effects that may occur, based on human studies, include a lupus-like syndrome, increased tear production, red/inflamed eyes, blood abnormalities, constipation, and 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 that are allergic to it or in pets with heart vessel disease, low blood pressure, severe dehydration, or severe blood loss. It should be used cautiously in pets with kidney disease, brain bleeds, or pre-existing autoimmune diseases. Use cautiously in pets that 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: ACE-inhibitors, beta-blockers, diazoxide, diuretics, furosemide, MAOIs, propranolol, or sympathomimetics.

Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this medication?

Prior to starting treatment, your veterinarian will take baseline chest X-rays so that changes may be monitored during therapy. Gum color, blood electrolyte levels, blood pressure, and blood cell counts may be monitored by your veterinarian 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?

It should be stored at room temperature and protected 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.

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