Hydroxyurea

What is hydroxyurea?

Hydroxyurea (brand names: Hydrea®, Droxia®, Mylocel®, Dacrodil®, Droxiurea®, Hydrine®, Litalir®, Medroxyurea®, Neodrea®, Onco-Carbide®, Oxeron®, Syrea®, Siklos®) is an antineoplastic medication used to treat certain types of cancers, such as polycythemia vera, mast cell tumors, meningioma, and leukemia. It may also be useful in treating feline hypereosinophilic syndrome and canine meningiomas.

Its use in cats and dogs to treat certain cancers is off label (extra label). 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 hydroxyurea given?

• Hydroxyurea is given by mouth in the form of a capsule.
• Give with food to limit side effects such as vomiting and diarrhea.
• A compounded liquid form may also be available; shake well before dosing and measure liquid forms carefully.

Hydroxyurea is considered a hazardous drug.

• If you are pregnant or nursing, do not handle this medication or waste from the treated pet.
• Wear gloves when handling this medication and when handling all bodily waste (urine, feces, blood, vomit, etc.) for several days after dosing this medication.
• Place gloves and contaminated waste in a sealable bag before disposing in the regular garbage.
• If skin or eye contact occurs while dosing this medication, wash carefully with soap and water or rinse eyes thoroughly.

This medication can take a few weeks before full effects are noted, but side effects can occur immediately. Gradual improvements are usually noticeable after a few days.

What if I miss giving my pet the medication?

This medication must be dosed very carefully to avoid toxicity, so if you miss a dose, contact your veterinarian for instructions.

Are there any potential side effects?

Hydroxyurea may cause the following side effects:

• Bone marrow suppression, which causes low blood cell counts (this side effect should be closely monitored by your veterinarian)
• Lack of appetite
• Vomiting
• Diarrhea
• Mouth and stomach ulcers
• Loss of toenails and/or hair coat
• Urinary problems

Serious adverse reactions may occur. If any of the following signs develop, stop giving hydroxyurea and contact your veterinarian immediately:

• Bleeding
• Bruising
• Fever
• Lethargy
• Coughing
• Difficulty breathing (due to lung damage)

Other side effects may occur. If you notice anything unusual, contact your veterinarian immediately. This moderate-acting medication should stop working in a few days, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

DO NOT USE hydroxyurea in pets that are:

• Allergic to it
• Pregnant (unless absolutely necessary)
• Lactating (unless absolutely necessary; use a milk replacer if used)

USE WITH CAUTION in pets that have:

• Anemia
• Bone marrow problems
• Active infection
• Lung disease
• Urate urinary stones
• Kidney disease
• A history of chemotherapy or radiotherapy

Are there any drug interactions I should be aware of?

Several medications should be used with caution when given with hydroxyurea, including:

• Myelosuppressive agents
• Vaccines

Certain medications may interact with hydroxyurea, so be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking before starting any new treatment.

Is any monitoring needed with this medication?

• Your veterinarian will perform bloodwork (complete blood count), including the number of platelets, at least every 1-2 weeks. Once stable, bloodwork should be monitored every 3 months.
• Your veterinarian will monitor kidney values before the start of treatment and then every 3-4 months.
• Your veterinarian may monitor your pet to be sure that the medication is working.
• At home, monitor for any side effects such as those noted above. Severe side effects could indicate toxicity. If you note any of these signs, contact your veterinarian, as this is an emergency.

How do I store hydroxyurea?

• Store capsules at room temperature between 68°F and 77°F (20°C and 25°C).
• Store away from light and in a tightly closed container.
• Store the compounded liquid at room temperature for up to 14 days, unless otherwise directed on 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. Be prepared to provide information about the product and your pet’s weight and symptoms.