The effects of topical ocular application of 0.25% demecarium bromide on serum acetylcholinesterase levels in normal dogs

Abstract

Objective: To assess the effects of topical ocular application of 0.25% demecarium bromide on serum acetylcholinesterase (ACHE) levels in normal dogs. Animals: Nine adult mixed breed dogs weighing between 18 and 27 kg. Procedures: Fifty μL of 0.25% demecarium bromide were applied to one eye of each dog every 8 h for 6 days. Blood was analyzed for AChE levels prior to commencement of eye drops, and at 45 min, 1 h 45 min, 4 h 45 min, 1 day, 3 days, and 7 days following commencement of eye drops using a 5,5′ -dithiobis-(2-nitrobenzoic acid) (DTNB) reaction. Results: Acetylcholinesterase levels declined over the first 24 h following commencement of demecarium administration in most dogs. This decline was highly variable and was statistically significant by 24 h. In some individuals AChE levels were suppressed to levels approaching clinical toxicity. By day 3 AChE levels had risen to levels above baseline in most dogs. Conclusions: Topical ocular application of demecarium causes transient suppression of systemic acetylcholinesterase levels in most dogs. Acetylcholinesterase levels generally do not fall to toxic levels, but may do so in certain individuals. Demecarium bromide eye drops generally do not cause AChE toxicity, but dogs receiving such therapy should be monitored for signs of AChE toxicity, and concomitant use of other AChE inhibitors should be avoided.