Pharmacokinetics of and serum thromboxane suppression by flunixin meglumine in healthy foals during the first month of life.

The research examined how the age of foals in the first month of life impacts the pharmacokinetic variables of flunixin, a nonsteroidal anti-inflammatory drug. The study also estimated the drug’s physiologic activity in the neonatal foals by observing flunixin’s effect on blood clotting.

Pharmacokinetics of Flunixin in Foals

• The researchers administered an intravenous dose of flunixin to five healthy foals at three different ages: 24-28 hours, 10-11 days, and 27-28 days. The variables studied included the area under the curve, mean residence time, zero-time intercept of the elimination phase, and several others.
• The results showed significant differences in these variables based on the age of the foals. For instance, the area under the curve, mean residence time, and zero-time intercept of the elimination phase were higher in foals aged 24-28 hours than in the older foals.
• Conversely, the elimination half-life and slope of the elimination phase were longer, while the total body clearance and zero-time intercept for the distribution phase were lower at the same age. The researchers used a biexponential equation for the best fit of plasma flunixin concentration for each foal at different ages.

Physiologic Activity of Flunixin in Foals

• Additionally, the study measured thromboxane B2 production, a process affected by flunixin, during the clotting of blood from the foals. This measure indicates the physiologic activity of the drug in neonatal foals.
• This production was significantly suppressed for 12 hours after flunixin administration at all ages. The authors concluded that even though the age of foals alters the disposition and elimination of flunixin, this may not have significant repercussions since the drug’s physiologic action on foals appears to be similar to its effect on mature horses.

In conclusion, while the study confirms that age affects the pharmacokinetics of flunixin in foals, this has little observable impact on the drug’s physiologic action during the first month of a foal’s life.