How glycopyrrolate injection affects dog tear test results

Abstract

OBJECTIVE To determine effects of glycopyrrolate administered IM on Schirmer tear test I (STT I) measurements in dogs. DESIGN Prospective clinical study. ANIMALS 13 client- and staff-owned dogs. PROCEDURES For both eyes of each dog, STT I measurements were recorded twice 20 minutes apart (at T1 and T2) and 2 to 4 hours later (at T3). Glycopyrrolate (0.01 mg/kg [0.005 mg/lb]) was administered IM to all dogs (3 dogs received an injection of saline [0.9% NaCl] solution on an earlier occasion), and final STT I measurements were recorded 20 minutes later (at T4). Intraocular pressures, heart rate, and respiratory rate were also recorded at each time point. RESULTS Ophthalmic variables did not differ between right and left eyes. In all dogs, variables at T1, T2, or T3 (measurements before glycopyrrolate administration) did not differ; baseline values were therefore defined at T3. At T4, STT I measurements were significantly decreased (mean ± SD decrease, 67.4 ± 15.4% [mean actual decrease, 15.8 mm/min]). During the same period, mean heart rate increased by 26.5 ± 12.0% (mean actual increase, 30.2 beats/min). Glycopyrrolate had no effect on intraocular pressure or respiratory rate. In 5 dogs at 24 hours after glycopyrrolate treatment, STT I measurement in each eye had returned to baseline value. Saline solution treatment (3 dogs) had no effect on any variables. CONCLUSIONS AND CLINICAL RELEVANCE In dogs, IM injection of glycopyrrolate resulted in a clinically relevant transient decrease in aqueous tear production. Application of lacrimomimetics beginning at the time of or within 20 minutes after glycopyrrolate premedication is recommended until STT I measurements return to baseline.