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Keywords:

  • brachycephalic;
  • corneal sensitivity;
  • naltrexone;
  • opioid growth factor receptor;
  • opioid-like growth factor;
  • tear production

Abstract

Objective

To determine the effect of topical naltrexone 0.3% on tear production, corneal sensitivity, and tear film stability in normal brachycephalic dogs.

Animals Studied

Twenty-two normal brachycephalic dogs.

Procedures

Measurements of tear production (Schirmer tear test I and II), intraocular pressure (IOP), central corneal sensitivity (CS), and tear film breakup time (TFBUT) were collected at time 0, 1, and 24 h after administration of either naltrexone (NTX) 0.3% or placebo (SV). Naltrexone or SV was then administered once daily for 1 week, and the above measurements were repeated at 7 days, then again 7 days after discontinuing medication. Owners scored the degree of comfort, redness, rubbing, squinting, and tearing. Serum was collected at time 0, 1, 24 h, and 7 days to determine systemic concentrations.

Results

Owners reported no significant change in the degree of comfort, redness, rubbing, squinting, or tearing. Naltrexone was detected in serum of all treated dogs 1-h postadministration (average: 908 pg/mL, range: 319–1570 pg/mL) and in two dogs at the 1-week time point. Naltrexone was not detected at the 24-h time point. There was no significant effect of NTX on STT1, STT2, IOP, CS, or TFBUT.

Conclusions

Naltrexone 0.3% is well tolerated and safe when applied topically to the eye once daily. Naltrexone 0.3% did not show any significant effects on corneal parameters as measured in this study. At once, daily dosing NTX is systemically absorbed; however, the degree of systemic absorption is not likely to be clinically significant.