Proin 75: Product Information

PROIN 75- phenylpropanolamine hydrochloride tablet, chewable
Pegasus Laboratories, Inc.

For oral use in dogs only

Caution: Federal law restricts this drug to use by or on the order of a licensed veterinarian.

Description: PROIN (phenylpropanolamine hydrochloride) is a sympathomimetic amine closely related to ephedrine.

Phenylpropanolamine hydrochloride (PPA) is the nonproprietary designation for benzenemethanol,α — (1-aminoethyl) — hydrochloride, (R*,S*) — , (± ).

The empirical formula is C9 H13 NO• HCl and the molecular weight is 187.67. It is a white crystalline compound having a slight aromatic odor.

PPA is freely soluble in water and alcohol but is practically insoluble in ether, benzene and chloroform. The chemical structure of phenylpropanolamine hydrochloride is:

Phenylpropanolamine Molecular Structure


PROIN is indicated for the control of urinary incontinence due to urethral sphincter hypotonus in dogs.

Dosage and Administration:

The total recommended dosage for oral administration is 2 mg/kg (0.91 mg/lb) of body weight twice daily. PROIN is scored and dosage should be calculated in half-tablet increments.


Not for human use. Keep out of reach of children. Consult a physician in case of accidental ingestion by humans.


PROIN may cause increased thirst; therefore, provide ample fresh water.

Overdose has been associated with dogs chewing through closed bottles of PROIN and consuming multiple tablets. Therefore, it is important to store PROIN Chewable Tablets out of reach of dogs and other pets in a secured location.

Use in dogs with incontinence due to a urinary tract infection will mask symptoms. PROIN is not effective in dogs with incontinence due to neurologic disease or malformations.

PROIN may cause hypertension; therefore, use with caution in dogs with pre-existing heart disease, hypertension, liver disease, kidney insufficiency, diabetes, glaucoma, and conditions with a predilection for hypertension. Use with caution in dogs receiving sympathomimetic drugs, tricyclic antidepressants, or monoamine oxidase inhibitors as increased toxicity may result. Use with caution in dogs administered halogenated gaseous anesthetics as this may increase the risk of cardiac arrhythmias.

A laboratory study on human blood revealed that PPA used in conjunction with aspirin may potentiate decreased platelet aggregation.

The safe use of PROIN in dogs used for breeding purposes, during pregnancy or in lactating bitches has not been evaluated.

Adverse Reactions “Pre Approval Experience”:

A placebo controlled clinical study involving 123 PROIN treated dogs and 61 placebo treated dogs was conducted for 28 days. The most common adverse reactions are shown in Table 1 below. In addition, one dog exhibited disorientation, nervousness, a 7.7% loss of body weight, and hypertension with proteinuria. A second dog exhibited restless behavior, lethargy, a 2.8% body weight loss and proteinuria.

Table 1: Number and percentage of dogs with adverse reactions in the 28 day placebo-controlled clinical study

Adverse Reactions PROIN Treated (N=123) Placebo Treated (N=61)
Emesis 20.3% 8.2%
Hypertension (≥ 160mm Hg)1 19.5% 14.7%
Anorexia 16.3% 3.3%
Body weight loss (> 5%) 2 16.1% 6.8%
Proteinuria 13.0% 8.2%
Anxiety/aggression/behavior change 9.7% 3.2%
Diarrhea 7.3% 9.8%
Polydipsia 6.5% 9.8%
Lethargy 5.7% 1.6%
Musculoskeletal Disorder 3.2% 1.6%
Insomnia/Sleep Disorder 2.5% 0.0%

1 One or more systolic blood pressure readings of ≥ 160mmHg.

2 The “N” for weight loss is PROIN treated N=118 and placebo N=59 because seven dogs did not have a final weight at the time of withdrawal from the study.

One-hundred fifty seven dogs continued into the 6 month open label clinical study. The most common adverse reactions are listed in Table 2 below. In addition, one dog exhibited progressively worsening hypertension with proteinuria. Five dogs enrolled in the study with pre-existing heart disease. Of these, one dog developed systolic failure with an unknown relation to treatment.

Table 2: Number and percentage of dogs with adverse reactions in the 6-month open-label clinical study

Adverse Reactions Total N= 125
Hypertension (≥ 160 mmHg)1 34.6%
Body Weight Loss (> 5%) 24.8%
Emesis 19.7%
Proteinuria 15.3%
Anorexia 10.2%
Diarrhea 6.4%
Lethargy 5.7%
Anxiety/ behavior change/ aggression 5.7%

1 Percent of dogs with systolic blood pressures of ≥ 160 mmHg on day 7 were 30.2% and on day 0 were 33.3%.


The following adverse events are based on voluntary, post approval reporting. Not all adverse events are reported to FDA/CVM. It is not always possible to reliably estimate the adverse event frequency or establish a causal relationship to product exposure using these data. The signs reported are listed in decreasing order of reporting frequency by body system:

Gastrointestinal: Vomiting, anorexia, diarrhea, hypersalivation,

Behavioral: Agitation, lethargy, vocalization, confusion,

General body system: Polydipsia, weight loss, weakness, fever,

Respiratory: Panting,

Dermatological: Erythema, piloerection,

Hepatic: Elevated serum alanine aminotransferase (ALT), elevated serum alkaline phosphatase (ALP),

Neurologic: Ataxia, seizures, tremors,

Renal/Urinary: Renal failure, hematuria, urinary retention,

Cardiovascular: Tachycardia, hypertension, bradycardia, arrhythmias,

Sensory: Ophthalmic disorders, mydriasis and eye redness.

In some cases, death, including euthanasia, has been reported. Sudden death was sometimes preceded by neurologic signs, vocalization, or collapse. A necropsy of one dog revealed subarachnoidal and intraventricular hemorrhage in the brain.

The following signs have been reported more often with a dose higher than the recommended dosage: agitation, arrhythmia, bradycardia, erythema, fever, hypersalivation, hypertension, lethargy, mydriasis, panting, piloerection, tachycardia, tremor, and urinary retention.

For a copy of the Safety Data Sheet (SDS) or to report suspected adverse drug events, contact Pegasus Laboratories at 1-800-874-9764. For additional information about adverse drug experience reporting for animal drugs, contact FDA at 1-888-FDA-VETS or

Information for Owner or Person Treating Animal:

Always follow the dosage instructions for PROIN provided by your veterinarian. Monitor your dog after giving PROIN to be sure all of it was consumed. If you have difficulty giving PROIN, contact your veterinarian.

It may take several days of treatment with PROIN before urinary incontinence improves. If you miss a dose, give it as soon as you remember. If it is close to the time for the next dose, skip the dose you missed and go back to the regular dosing schedule. Do not give two doses at once. PROIN should only be given to the dog for which it was prescribed. Because PROIN is flavored, store in a secure area.

Dogs may willingly consume more than the recommended dosage of PROIN Chewable Tablets. Instances of dogs chewing through closed bottles of PROIN and eating the bottles contents have been reported. Keep the product in a secured storage area out of the reach of pets in order to prevent accidental ingestion or overdose. Contact your veterinarian immediately if the dog ingests more tablets than prescribed or if other pets ingest PROIN Chewable Tablets. In the case of accidental ingestion by humans, contact a physician immediately.

Contact your veterinarian if you notice restlessness or irritability, loss of appetite, the incontinence persists or worsens, or any other unusual signs.

Consult your veterinarian before using PROIN with any other medications.

Clinical Pharmacology:

Phenylpropanolamine is a chemical analogue of the endogenous sympathomimetic amines. It is an alpha-adrenergic agent which has been reported to increase urethral tone in dogs. 2 Its mechanism of action is not well determined, but it is believed to cause the release of norepinephrine by indirectly stimulating both the alpha and beta-adrenergic receptors of the smooth muscle to increase smooth muscle tone of the urethra, bladder neck, and the internal urethral sphincter. 3, 4

The pharmacokinetics of phenylpropanolamine in dogs has not been well studied. In humans, phenylpropanolamine is readily absorbed after oral administration of solid dosage forms and has an onset of action of approximately 15-30 minutes and duration of effect of about three hours. In a published study in dogs, phenylpropanolamine disposition was characterized in three dogs administered phenylpropanolamine intravenously and orally in immediate-release and controlled-release formulations. 5 The terminal elimination half-life averaged 3.5 ± 0.5 hours after the intravenous dose. Oral absorption from the immediate-release capsule was rapid and bioavailability was 98.2 ± 6.9 percent. Absorption of phenylpropanolamine from the controlled-release dosage form was biphasic; an initial rapid phase was followed by a second, slower absorption phase which continued over 16 hours. Plasma concentrations then declined with a half-life roughly parallel to the intravenous and oral immediate-release half-lives. Oral bioavailability from the controlled-release tablet was 93.7 ± 5.9 percent.

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