RESUMO
The choice of analgesic agents for the horse is limited, and many have side effects that can restrict their use for chronic and prolonged pain. Little information has been published on tramadol and acetaminophen use in the horse. The study evaluated the analgesic effects of coadministration of tramadol and acetaminophen compared to those of each drug individually in a crossover study. The study was performed on six healthy horses each infused with the following over 1 hour: control (normal saline), tramadol, acetaminophen, or both (acetaminophen and tramadol infused together). Nociception (using a pressure algometer) and any adverse effects were evaluated before the infusion, at 0, 10, 20, 30, 40, and 50 minutes during the infusion and at 15, 30, and 60 minutes after infusion completion. The pressure algometer was placed on the palmar surface of both the forelimbs. There was no difference in response to nociception between the control and single-agent (acetaminophen or tramadol) groups. However, coadministration of tramadol and acetaminophen resulted in a significant analgesic effect from 20 minutes after starting the infusion until the infusion was completed. Fifteen minutes after discontinuing the infusion, no significant differences remained between the groups. No side effects were seen, with the exception of one horse in the coadministration group which showed paroxysmal ventricular tachycardia 30 minutes after constant rate infusion (CRI) which resolved completely after discontinuing the infusion. Simultaneous infusion of tramadol and acetaminophen resulted in significant analgesia. Further research is required to evaluate its effect and possible side effects in clinical cases, such as horses suffering from laminitis.
