Pharmacokinetics and competitive pharmacodynamics of ADP-induced platelet activation after oral administration of clopidogrel to horses.

This research explores how a single dose of clopidogrel, an oral medication, impacts a horse’s platelet activity and how the drug circulates through the horse’s body. The findings reveal a temporary reduction in platelet collection within four hours of intake, but no significant change is seen 24 hours later. Consequently, the need for more frequent dosage compared to other species is suggested due to rapid elimination of the drug.

Study Design and Methodology

• The study included six healthy adult horses as participants.
• The researchers administered a single oral dose of clopidogrel (2 mg/kg), then collected blood samples at different intervals up to 24 hours.
• They gauged the reactivity of the platelets in each sample using optical aggregometry and assessed the phosphorylation of a protein called vasodilator-stimulated phosphoprotein (VASP).
• The team used liquid chromatography-tandem mass spectrometry to measure the concentrations of clopidogrel and its active metabolite derivative (CAMD) in all blood samples.
• The pharmacokinetic parameters, which include factors like the time taken to reach maximum concentration and half-life of the drugs, were determined using a non-compartmental model.

Key Results

• The study found a significant reduction in platelet aggregation (collection of platelets) in response to a 12.5μM concentration of ADP, a compound that induces platelet activation, just four hours after clopidogrel administration in five of six horses.
• No change in platelet aggregation was observed 24 hours after the drug’s administration.
• There was no change in platelet aggregation either in response to a 25μM concentration of ADP before and after administration.
• Phosphorylation of VASP, a process linked to platelet activation, stimulated by ADP and a hormone called prostaglandin E, was not affected by the administration of clopidogrel.
• The time taken to reach maximum concentration of clopidogrel and CAMD was approximately half an hour and around 42 minutes respectively, indicating rapid absorption of the drug.
• The calculated terminal-phase half-life, the time it takes for the concentration of the drug to decrease by half, was almost 1.81 hours for clopidogrel and just under an hour for CAMD, suggesting a relatively quick elimination from the horse’s body.

Conclusion

• The study concludes that a single dose of clopidogrel or its active metabolite derivative (CAMD) caused competitive disruption of ADP-induced platelet aggregation during the first 24 hours after administration.
• However, given the rapid elimination of the CAMD from the horse’s body, the researchers suggest that the administration of clopidogrel may be needed more frequently in horses compared to other species where the drug causes long-term inhibition of platelets.