PHENYLPROPANOLAMINE

(for veterinary information only)

BRAND NAME: PROIN, PROPALIN

AVAILABLE IN
25 mg, 50 mg, & 75 mg
CHEWABLES

BACKGROUND

In order to understand how phenylpropanolamine works in the body, it is important to understand some background regarding the “autonomic nervous system.” The autonomic nervous system can be thought of as the “automatic” nervous system in that it controls physiologic functions that one is not aware of. Examples include sweating during times of anxiety, increases and decreases in heart rate or respiratory rate, dilation or constriction of the pupils, blood pressure changes and other functions that enable us to adapt to our changing environment as we perceive it. Our nervous system controls all these things yet we are not consciously aware of any of them happening thanks to the autonomic nervous system.

The autonomic nervous system is divided into the “sympathetic” and the “parasympathetic” portions. The easiest way to think of these divisions is that the parasympathetic system maintains the “status quo” of the body while the sympathetic system initiates changes that are adaptive in times of stress (the so-called “fight of flight” response.)

The sympathetic nervous system is where phenylpropanolamine acts as a stimulant promoting the “fight or flight” reflexes within the body. This means that phenylpropanolamine has many effects and thus many uses in the treatment of disease. Its relative safety and efficacy made it a common over-the-counter decongestant for human use once upon a time while its appetite suppression side effect lead to its wide employment as a human dieting/weight loss aid.

It was accessible in numerous forms on the shelves of every drug store in America but two problems changed all that. The first problem is that this drug was found to cause an increase in the incidence of strokes and cerebral hemorrhage in people age 18-49. The second problem is that phenylpropanolamine can be used in the illegal production of methamphetamine. The drug was withdrawn from the human market and restrictions have been placed on quantities of the veterinary product that can be ordered. In some states it is considered a controlled substance.

In veterinary medicine, phenylpropanolamine is used almost exclusively for the control of urinary incontinence in dogs and occasionally in cats. Phenylpropanolamine is able to increase sphincter tone in the urethra thus curtailing inadvertent urine leakage. The increase in high blood pressure that was problematic in humans is not considered a significant issue to the pet population.

HOW THIS MEDICATION IS USED

Phenylpropanolamine is generally used 2-3 times daily for control of urinary incontinence. Only occasionally is this medication used as a decongestant in animals. If a dose is accidentally skipped, do not double up on the next dose. Simply give the medication when it is remembered and time the next dose according to the instructions.

INTERACTIONS WITH OTHER DRUGS

In some cases of urinary incontinence, phenylpropanolamine is used in combination with estrogens (such as diethylstilbesterol or estriol). No harmful drug interactions are expected with this combination. In fact, they synergize for a stronger effect.

Phenylpropanolamine should not be used with L-Deprenyl (Anipryl)
nor with Amitraz containing tick control products due to resulting
unpredictable fluctuations in blood pressure.
It is recommended that phenylpropanolamine be withdrawn
for 2 weeks preceding the use of either of these products and vice versa.

An increased risk of hypertension can also occur if phenylpropanolamine is given in conjunction with tricyclic antidepressants (such as amitriptyline  or clomipramine), non-steroidal anti-inflammatory drugs (NSAIDs), or amitraz (active ingredient of several tick control products. See our tick comparison chart for details).

SIDE EFFECTS

Phenylpropanolamine stimulates a “fight or flight” response. This means that the following effects may be observed: rapid heart rate, elevation in blood pressure, and restlessness. Appetite loss or reduction may be a problem. An increase in thirst is also a common side effect.

Irritability and restlessness are documented side effects that can occur in humans. It is reasonable to consider that this medication may create similar effects in our pets. Other side effects generally not considered to be serious include: mild upset stomach (generally controlled by giving the medication with food), dilated pupils, panting, increased thirst.

Potentially serious side effects would include high blood pressure (hypertension). This is rarely an issue in pets but potentially could happen. Urinary protein loss has also been reported.

CONCERNS AND CAUTIONS

When initiating therapy with phenylpropanolamine, it is important not to expect an immediate change in urinary incontinence. Several days of proper dosing will be needed before effect can be assessed.

Before using phenylpropanolamine to control urinary incontinence, it is important to rule out other medical causes of incontinence such as kidney disease and bladder infection. These latter conditions are progressive and should be identified early in their course for meaningful treatment results.

Phenylpropanolamine should be stored in containers which protect it from light. Light exposure leads it to lose potency.

Phenylpropanolamine acts by causing the release of a hormone and neurotransmitter called “norepinephrine.” With chronic use, it is possible to deplete the body’s stores of norepinephrine and the patient will appear to become “resistant” to the effects of the drug. This phenomenon is well described in people who use phenylpropanolamine as a decongestant but it is unclear as to whether this occurs in dogs and cats.

Because of its effects in elevating heart rate and blood pressure,
phenylpropanolamine should not be used in patients with heart disease
or pre-existing high blood pressure.
This includes patients with glaucoma, hyperthyroidism, and diabetes mellitus
as well as those with certain types of cardiovascular disease.
Check with your veterinarian if there is any question.

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Page last updated: 10/14/2021