Objective evaluation of the systemic effects of topical application of 1% atropine sulfate ophthalmic solution in healthy horses.

This research investigated the safety of using a 1% atropine eye solution in healthy horses, measuring its possible impacts on the gastrointestinal system. The researchers found that this eye application didn’t cause any related issues or adverse effects.

Research Design

• The researchers organized a randomized, controlled crossover study with six adult geldings (castrated male horses).
• Three horses were randomly chosen to first receive the atropine treatment in the left eye, while artificial tears were administered to the left eye of the other three – their right eyes were left untreated.
• The treatment was administered every 6 hours for a day, and then decreased to every 12 hours for four more days.
• The horses were also administered 200 non-toxic beads via a tube placed into their stomach through their nose (nasogastric intubation) in order to track changes in their gastrointestinal transit.

Data Collection and Monitoring

• The researchers observed and recorded the horses’ reactions to light in their pupils (pupillary light reflexes), pupil dilation (mydriasis), heart rate, the movement of the beads through their stool, and signs of abdominal pain.
• The horses’ abdominal girth measurements, the sounds their guts made (auscultable gut sounds), fecal weight were also monitored.
• After a four-week period, the horses received the opposite treatment in their left eye, and the whole monitoring process was repeated.
• The concentration of atropine (to detect systemic absorption) in the horses’ blood was measured using an ELISA test at various points after the atropine was first administered.

Results

• No horse showed any signs of colic (severe, often fluctuating pain in the abdomen) or ileus (disruption in the normal movement of the digestive tract) at any time during the study.
• Complete dilation of the left eye pupils with absence of the pupillary light reflex was observed in five horses within six hours, and in all six horses within 12 hours of atropine application.
• Only one horse showed pupil dilation and absence of the reflex in the untreated eye by the fifth day of applying atropine.
• No atropine was detected in the blood samples of any horse, confirming that no systemic absorption took place.

Conclusions and Clinical Relevance

• The researchers concluded that topical atropine application at clinically appropriate doses did not cause any disruption or problems in the gastrointestinal function of healthy horses.
• This findings could give confidence to veterinarians to use this medication without the worry of inducing harmful effects on the horse’s digestive system.