Overview Phenoxybenzamine for Canines and Felines

Phenoxybenzamine, Dibenzyline® is used in dogs and cats to relax the smooth muscle of the urinary bladder sphincter. 

Phenoxybenzamine is in the class of drugs known as alpha-adrenergic blocking agents. These drugs block or reverse the effects of alpha-receptor stimulation.

Alpha-adrenergic receptors respond to the body chemicals epinephrine and norepinephrine. Stimulation of alpha-receptors leads to constriction of blood vessels and increased tone of smooth (involuntary) muscle in other body organs. Blood vessel constriction increases blood pressure.

Phenoxybenzamine blocks the effects of alpha-adrenergic receptors, resulting in dilation of the blood vessels. This drug also reduces the tone of smooth muscle in organs such as the bladder.

Phenoxybenzamine is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.

This drug is not approved for use in animals by the Food and Drug Administration but it is prescribed legally by veterinarians as an extra-label drug.

Brand Names and Other Names of Phenoxybenzamine

This drug is registered for use in humans only.

Human formulations: Dibenzyline® (SKF)

Veterinary formulations: None

Uses of Phenoxybenzamine for Dogs and Cats

The most common use of this drug is to relax the smooth muscle of the urinary bladder sphincter.

Phenoxybenzamine has been used to treat high blood pressure associated with epinephrine-secreting tumors.

Precautions and Side Effects

While generally safe and effective when prescribed by a veterinarian, phenoxybenzamine can cause side effects in some animals.

Phenoxybenzamine should not be used in animals with known hypersensitivity or allergy to the drug.

Phenoxybenzamine should be avoided in patients with low blood pressure.

It should be used with caution in animals with heart failure or kidney damage because it may lower blood pressure and reduce blood flow to the kidneys.

Phenoxybenzamine may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with phenoxybenzamine. Such drugs include epinephrine.

Adverse effects of phenoxybenzamine include low blood pressure, increased heart rate, nasal congestion, weakness and dizziness.

How Phenoxybenzamine Is Supplied

Phenoxybenzamine is available in 10 mg capsules. Accordingly, doses are rounded to the nearest 2.5 mg. It is commonly compounded into a lower concentration for use in smaller dogs and cats. 

Dosing Information of Phenoxybenzamine for Dogs and Cats

Medication should never be administered without first consulting your veterinarian.

The typical dose for dogs is 5 to 20 mg total, once to twice daily.

The typical dose for cats is 2.5 mg to 7.5 mg total, once to twice daily.

The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your pet feels better, the entire treatment plan should be completed to prevent relapse or prevent the development of resistance.