Pharmacokinetics, penetration into cerebrospinal fluid, and hematologic effects after multiple oral administrations of pyrimethamine to horses.

The research article is about a study on how the drug pyrimethamine, when given orally, affects horses over multiple uses, focusing on how much of the drug reaches the brain, how it accumulates in the blood, and how it affects the horse’s blood cells.

Pharmacokinetics and Accumulation in Plasma

• The study involved administering pyrimethamine, a dose of 1mg/kg of the horse’s body weight, orally to five adult horses daily for ten days.
• Blood samples were taken after the first, fifth, and tenth doses to understand how the drug was processed (pharmacokinetics) by the horse’s body over time.
• Findings indicated that prolonged daily usage led to pyrimethamine accumulation in the plasma (the liquid part of the blood), reaching a steady state within five days. Further, post the fifth day, the average maximum concentration of pyrimethamine in the plasma was more than double the concentration after the first dose.

Penetration into Cerebrospinal Fluid (CSF)

• The study also aimed to assess how much of the drug reached the horse’s brain.
• CSF samples, which were obtained from the horses 4 to 6 hours after the first, third, seventh, and tenth doses, were used to conduct this analysis.
• The research found that the concentration of pyrimethamine in the CSF was about 25-50% of the corresponding plasma concentration.
• There was no significant buildup of the drug in the CSF with repeated administration of the doses, unlike plasma.

Hematologic Effects

• The last part of the study analyzed blood samples collected during and after the dosing regimen to understand if the drug had any hematologic effects, i.e., if it influenced the blood cells in any manner.
• The study found a slight decrease in the number of neutrophils (a type of white blood cell crucial for fighting off infections).
• However, despite the decrease, the neutrophil count remained within a normal range for adult horses, implying that pyrimethamine did not significantly affect the horse’s immuno-response.