Effect of plasma fibrinogen concentration on the inhibition of platelet aggregation after ticlopidine compared with aspirin.
OBJECTIVE
Elevated levels of plasma fibrinogen are a risk factor for cerebral infarction. Because fibrinogen plays a central role in platelet aggregation and binding of fibrinogen to platelets is inhibited by ticlopidine, we studied the effect of the plasma fibrinogen concentration on the antiaggregatory action of ticlopidine compared with that of aspirin.


METHODS
We determined platelet aggregability before and after administration of ticlopidine (200 mg/d) or aspirin (81 mg/d) in 61 stroke patients and correlated the changes with the plasma fibrinogen concentration.


RESULTS
In patients receiving ticlopidine, the platelet aggregability induced by 1, 5, and 10 mumol/L adenosine diphosphate significantly decreased compared with aggregability before medication (P < .05), and the reductions had significant negative correlations with the plasma fibrinogen concentration (P < .05). In patients receiving aspirin, the platelet aggregability induced by 2 micrograms/mL collagen and 5 and 10 mumol/L adenosine diphosphate decreased compared with aggregability before medication (P < .005), but the reductions had no significant correlation with the plasma fibrinogen concentration.


CONCLUSIONS
The relative antiaggregatory effect of ticlopidine is significantly decreased with higher plasma fibrinogen concentrations. This may explain, at least in part, the individual variation in the response to ticlopidine.
Tohgi
H
H
Department of Neurology, Iwate Medical University, Morioka, Japan.
Takahashi
H
H
Kashiwaya
M
M
Watanabe
K
K
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000368:Aged; D001241:Aspirin / Q000494:pharmacology*; D002544:Cerebral Infarction / Q000097:blood / Q000188:drug therapy; D002561:Cerebrovascular Disorders / Q000097:blood* / Q000188:drug therapy; D003094:Collagen / Q000494:pharmacology; D005260:Female; D005340:Fibrinogen / Q000032:analysis* / Q000502:physiology*; D006801:Humans; D008297:Male; D010974:Platelet Aggregation / Q000187:drug effects* / Q000502:physiology; D010976:Platelet Count / Q000187:drug effects; D013988:Ticlopidine / Q000494:pharmacology*
D000244:Adenosine Diphosphate; D005340:Fibrinogen; D003094:Collagen; D013988:Ticlopidine; D001241:Aspirin