Interactions between chloramphenicol, acepromazine, phenylbutazone, rifampin and thiamylal in the horse.

The research analyzes the potential interactions of certain drugs in horses, showing that chloramphenicol, in particular, can significantly influence anaesthesia duration and elimination rate of phenylbutazone.

Overview of Research

• The study aimed to understand how certain drugs interact with each other when administered to horses – more specifically, the interactions between chloramphenicol, acepromazine, phenylbutazone, rifampin, and thiamylal.
• Two sets of experiments were conducted to evaluate these interactions.

First Experiment

• In the initial round of experiments, five horses were intravenously given thiamylal (an anesthetic) after pretreatment with acepromazine (a tranquilizer).
• The primary focus here was to determine the time of recumbency, which is the period when the horse is lying down post-anesthesia.
• The researchers found that when chloramphenicol (an antibiotic) was administered intravenously one hour prior to anesthesia, it significantly extended the recumbency period from an average of roughly 22 minutes to approximately 36 minutes.
• Administration of phenylbutazone (a non-steroidal anti-inflammatory drug) intravenously for four days prior to anesthesia showed a decrease in recumbency time, but the decrease was not statistically significant.

Second Experiment

• In the second round of experiments, phenylbutazone, chloramphenicol, and rifampin (an antibiotic) were administered in varying sequences to another set of five horses.
• The goal here was to study the impact of these drug combinations on the elimination rate of phenylbutazone.
• The results showed that pretreatment with chloramphenicol led to a significant decrease in the elimination rate of phenylbutazone, while rifampin significantly increased its elimination rate.
• The half-life of phenylbutazone elimination alone was around 4 hours, whereas with rifampin pretreatment for four days, it fell to approximately 2.7 hours. On the contrary, it increased to nearly 5.6 hours and 9.5 hours respectively when one and two doses of chloramphenicol were administered prior to phenylbutazone.