Overview of Phenylephrine for Dogs and Cats

Phenylephrine HCl, commonly known as Ak-Dilate® or Ak-Nephrin®, is an agent used to dilate the pupil in dogs and cats. Pupil dilation is performed during some portions of an eye examination. Phenylephrine may also be used with other drugs such as atropine, to dilate the pupil prior to certain eye surgeries.

Phenylephrine belongs to a class of drugs known as alpha-receptor agonists that are similar in structure to epinephrine. Phenylephrine has minimal effect on beta-receptors.

Phenylephrine 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 (FDA), but it is prescribed legally by veterinarians as an extra-label drug.

Brand Names and Other Names of Phenylephrine

This drug is registered for use in humans only.

Human formulations: Ak-Dilate® (Akorn), Ak-Nephrin® (Akorn), Phenylephrine sterile ophthalmic solution® (Medical Ophthalmics), Phenylephrine HCl ophthalmic solution® (Bausch & Lomb), and various generic preparations.

Veterinary formulations: None

Uses of Phenylephrine for Dogs and Cats

Phenylephrine is used to help examine the lens and posterior segment of the eye. For examination purposes, it is usually combined with the short-acting pupil dilator, tropicamide.

Phenylephrine is often used with atropine in the treatment of certain eye diseases, especially when the pupil is unresponsive to atropine alone.

Phenylephrine is used to assess hyperemia of the eye.

Phenylephrine can be used to help determine the site of neurologic damage in Horner’s syndrome.

Precautions and Side Effects

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

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

Phenylephrine should not be used in cases of overt glaucoma, or in animals predisposed to glaucoma.

Phenylephrine also should not be used in the presence of lens luxation (when the lens separates from its attachments within the eye).

Phenylephrine can be irritating when applied topically, with animals exhibiting redness and blinking immediately after application.

Phenylephrine is also potentially toxic to the corneal epithelium, particularly in cats. When repeatedly applied to the eye, phenylephrine can cause transient clouding of the cornea.

Phenylephrine may interact with other medications. Consult your veterinarian to determine if other drugs your pet is taking could interact with phenylephrine. Such drugs include local anesthetic agents used on the eye, such as proparacaine and tetracaine.

How Phenylephrine Is Supplied

Phenylephrine HCl is available as a 0.12% solution (Ak-Nephrin®) in 15 ml bottles, a 2.5% solution in 2 ml, 5 ml and 15 ml bottles.

It is also available as a 10% solution in 5 ml bottles.

Dosing Information of Phenylephrine for Dogs and Cats

Medications should never be administered without first consulting your veterinarian.

When used to diagnose Horner’s syndrome, one drop of 0.1 to 0.12% solution is applied to the eye once.

When used with tropicamide to facilitate pupil dilation during ophthalmic examinations, one drop of 2.5% phenylephrine is applied once or twice 5 minutes apart.

When used with atropine, phenylephrine is generally applied a maximum of 4 times daily, and less often in animals under 12 pounds. Systemic absorption of phenylephrine in small animals may change their heart rates.

The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be sure to closely follow your veterinarian’s instructions as to the frequency and duration of this medication.