Effects of intramuscular chlorpromazine alone and chlorpromazine–morphine combination on Schirmer tear test results in clinically normal dogs

Abstract

The objective of this study was to evaluate effects of intramuscularly administered chlorpromazine alone and chlorpromazine–morphine combination on Schirmer tear test (STT) results in clinically normal dogs. Fourteen dogs free of clinically relevant ocular abnormalities were used in this study. STTs were performed and the dogs were injected intramuscularly with chlorpromazine alone (group C) and chlorpromazine–morphine combination (group CM). STTs were repeated 15, 25, 60, and 120 mins later. Aqueous tear production in dogs, measured by STT, was significantly reduced in both treatment groups 60 and 120 min after injection of the drugs. The mean ± SD STTs for the baseline time for chlorpromazine alone (group C) and chlorpromazine–morphine (group CM) were 19.4 ± 4.4 and 15.7 ± 4.0 wetting per minute, respectively. For group C, the subsequent mean ± SD STT levels were 18.78 ± 2.49 (15 min), 16.35 ± 4.79 (25 min), 13.71 ± 4.66 (60 min), and 14.14 ± 4.42 (120 min). For the CM group, the subsequent mean ± SD STT levels were 13.50 ± 6.09 (15 min), 11.57 ± 5.29 (25 min), 10.00 ± 4.16 (60 min), and 9.42 ± 5.23 (120 min). In conclusion, a single intramuscular dose of chlorpromazine alone or chlorpromazine–morphine combination significantly reduces tear production rates as measured by the STT in normal dogs.