The mode for the manifestation of the inhibitory effects of ifenprodil tartrate on platelet aggregation in vivo and ex vivo

The mode for the manifestation of the inhibitory effect of ifenprodil tartrate on platelet aggregation in vivo and ex vivo was studied in mice and men, respectively. The ifenprodil level in plasma reached the maximum in 20 min after oral administration of 30 mg ifenprodil tartrate/kg in mice, and it decreased over a 3 hr period after the administration. On the other hand, the maximal inhibitory effect was observed 60 min after the administration. Thus ifenprodil tartrate manifested its inhibitory effect on platelet aggregation only after the maximum plasma concentration of ifenprodil was reached. The same phenomenon was observed with the inhibitory effects of ifenprodil tartrate on platelet aggregation ex vivo in man. To clarify the reason for the delay in the manifestation of the inhibitory effects of ifenprodil, the ifenprodil contents in mouse platelets after the oral administration of the drug was measured. The pattern of change in the ifenprodil contents in platelets was found to resemble closely the pattern of the change in its inhibitory effects, suggesting that the manifestation of the inhibitory effects on platelet aggregation by oral administration of ifenprodil tartrate was directly related to the ifenprodil contents in platelets rather than the ifenprodil level in plasma.