Seasonal Fluctuation in Adhesive Platelets during Long‐Term Anticoagulant Therapy*

Abstract

A mono‐amine oxidase inhibitor (Nialamide) has been shown to reduce the extent of induced thrombosis in experimental animals, and to enhance the anticoagulant effects of both phenindione and warfarin (Shimamoto, Yamazaki, Tsuchihashi and Sunaga, 1961; Shimamoto, Ishioka and Jujita, 1962), but these effects were apparent for only a few hours after administration of the drug. Maschouf, Robinson and LeBeau (1964) were able to demonstrate a rapid reduction in platelet adhesiveness in human subjects following a single dose of 75–100 mg., but long‐term treatment of patients with Nialamide alone in doses of 75–200 mg. daily, or in doses of 75 mg. daily in combination with phenindione, had no obvious effect on the total platelet count, or on the adhesive or non‐adhesive platelet count (Eastham, 1964b; Maschouf et al., 1964). Control platelet counts taken from male patients on long‐term anticoagulant therapy with phenindione alone appeared to show some seasonal fluctuation. These results have therefore been examined in detail over a 14‐month period.

The irrelevance of adhesive platelet estimations after thrombosis

“…Unfortunately no useful prognostic value was obtained from total or adhesive platelet counts during long-term oral anticoagulant therapy (Eastham, 1966;Eastham and Avis, 1966). In an individual the total platelet count has been shown to vary about a mean value by an average of 10 to 15% and the corresponding ADP-induced adhesive platelet count to vary by an average of 25 to 30% (Eastham, 1966).…”

“…The evidence that platelet adhesiveness alters because of uncontrollable platelet variables and is controlled at least in part by plasma factors is discussed. The possibility of measuring the plasma factors is considered briefly.Estimation of platelet adhesiveness has not been found to be clinically useful either during longterm anticoagulant therapy (Eastham, 1966;Eastham and Avis, 1966) or in the detection of venous thrombosis after surgery (Negus, Pinto, and Brown, 1969). A reassessment of this absence of obvious clinical significance has now been attempted, as there is evidence that the degree of platelet adhesiveness can change rapidly without any variation in the total platelet count, and because it now appears that platelet adhesiveness is greatly influenced by plasma factors (Bennett, 1968; Besterman, Myat, and Travadia, 1967;Bolton, Hampton, and Mitchell, 1967).…”