Pharmacokinetics and pharmacodynamics of a high concentration of buprenorphine (Simbadol) in conscious horses after subcutaneous administration.

The research investigates the effects and efficiency of a high-concentration buprenorphine, known as Simbadol, as a subcutaneous treatment in horses. The study concluded that while Simbadol has potential for pain relief in horses, its side effects and short-term relief do not surpass those of a standard dose of buprenorphine.

Research Methodology

• A group of six healthy adult horses, each weighing between 521 and 602 kilograms, were involved in a randomized, crossover trial.
• The horses underwent three treatments, each at least a week apart and randomly administered. These treatments include Simbadol with dosages of 0.005 mg/kg (S5) and 0.0025 mg/kg (S2.5), and a saline solution (SAL).
• Electrical nociceptive threshold (ENT), physiological variables, locomotive activity, degrees of restlessness, and signs of excitement were monitored and measured before and after 48 hours of each injection.
• Blood samples were collected for pharmacokinetic analysis to measure buprenorphine concentration in their plasma using a method known as liquid chromatography-tandem mass spectrometry.

Research Findings

• Buprenorphine was detected in all the horses from 15 minutes after administration up to 8-12 hours.
• The ENT was significantly higher in the S2.5 treatment group compared to the SAL group at 0.75-6 hours after treatment, indicating increased pain threshold.
• All horses exhibited increased locomotive activity and compulsive behavior after Simbadol treatment. The S5 treatment group also showed a significant increase in restlessness which lasted longer than in the SAL group.
• Gastrointestinal mobility was significantly reduced in all horses treated with Simbadol, returning to normal after approximately 16 hours.

Conclusions

• Simbadol was quickly absorbed and rapidly decreased when administered subcutaneously.
• Both Simbadol treatments led to side effects typically seen in horses after opioid administration, with the S5 treatment causing a longer period of excitement.
• There is potential for Simbadol (0.0025 mg/kg) to be used to treat pain in horses, as a clinical treatment. However, the duration of its pain relief effects was not found to be longer than the conventional buprenorphine’s effects, and it caused side effects, such as decreased gastrointestinal motility and increased locomotor activity.