The disposition and metabolism of the synthetic prostaglandin fluprostenol (ICI 81,008) in the horse.

The research investigates how the drug fluprostenol, a synthetic prostaglandin, is processed and absorbed in the horse’s body. The study focuses on its behavior in the bloodstream, salivary glands, and its excretion patterns in male and female horses.

Drug Administration and Blood Plasma Results

• The drug fluprostenol was administered to three female and three male gelded horses. The horses received single doses via an intramuscular injection, after which the plasma was analyzed for drug concentrations.
• The researchers found that the drug quickly enters the bloodstream, with observable radioactivity detected in the plasma within five minutes post-injection.
• Maximum drug concentration in the plasma varied but was witnessed between 5 and 90 minutes after injecting. For instance, the equivalent of fluprostenol ranged between 0.32 and 1.30 ng/ml.
• Interestingly, the residual radioactivity of the drug could still be observed in the female horse’s plasma after three days.

Saliva Concentration

• Notably, the drug was also found in the parotid saliva of the male gelded horses as soon as 10 minutes after administration. The peak concentration in saliva was detected within 1 hour post-administration.
• The concentration ratios between saliva and plasma were dependent on the saliva flow rate. With higher saliva flow rates, it showed less concentration.

Excretion of Fluprostenol

• Fluprostenol excretion was largely done through urine, with the process being rapid and nearly complete 12 hours post-dosing.
• Female horses had excreted 45% of the drug’s radioactivity through urine after 96 hours, while gelded male horses excreted 53% after 30 hours. Approximately 30% of this excreted radioactivity was unchanged fluprostenol.
• The study also showed that fecal excretion played a part, with the female horses excreting approximately 32% of the administered radioactivity this way within 2 days.
• As for tissue concentrations of the drug, the traces were below detection limits in female horses after four days. However, traces of 0.2-0.9% of the dose were detected at the injection site.