Phenylpropanolamine (Proin) increases intraocular pressure and alters tear production in dogs

To determine the effect of phenylpropanolamine (PPA; Proin) on intraocular pressure (IOP) and Schirmer tear test-I (STT-I) values in dogs.

Following baseline ophthalmic examinations, including IOP and STT-I measurements, 6 healthy, purpose-bred intact female Beagles aged 7.5 to 10 months were orally administered PPA at 2 mg/kg twice daily over a 4-week period. Intraocular pressure was measured twice weekly at 8:00 am, 12:00 pm, and 4:00 pm. Schirmer tear test-I was measured once weekly. A complete ophthalmic examination was conducted every 2 weeks. Intraocular pressure measurement continued once weekly for a 2-month period following discontinuation of PPA. Descriptive data are presented as mean ± SE of the mean.

Compared with pretreatment IOPs (20.8 ± 0.5 mm Hg), values showed a statistically significant increase (23.0 ± 0.3 mm Hg and 21.9 ± 0.3 mm Hg during and after administration, respectively), whereas STT-I values in the right eye showed a statistically significant decrease during PPA administration. Although none of these changes were clinically relevant, dogs with high baseline IOPs exhibited greater fluctuation with elevated IOPs following PPA administration.

PPA administration induced an increase in IOP and exacerbated IOP fluctuation in dogs with high baseline IOP. Phenylpropanolamine should be prescribed with caution in patients with elevated baseline IOP or those predisposed to glaucoma.

These findings highlight the importance of monitoring IOP in dogs receiving PPA, particularly those with ocular hypertension or a predisposition to glaucoma, to ensure safe clinical use.