Human Pharmacology Studies in Volunteers with Indobufen (K 3920), Inhibitor of Platelet Aggregation

Given by the i.v. route to healthy volunteers, indobufen has an half-life of 7-9 h. After oral administration of tablets, the drug is completely absorbed. Excretion occurs through the kidney and the drug is present in the urine as glucoronide and in unchanged form. The maximum inhibitory effect on collagen-induced platelet aggregation was observed 1 to 4 h after i.v. and p.o. administration but activity at 8 h was more marked after p.o. administration in accordance with the higher plasma levels found at that time. During repeated administration at the dose of 100 mg b.i.d. for 7 days, no important changes in kinetic parameters and activity of indobufen was observed. Indobufen is rapidly absorbed also when given by the i.m. route, giving at 30 min peak levels comparable to those observed after oral administration. These data suggest that indobufen is active by the i.V., p.o. and i.m. routes, that its effect on platelets, unlike ASA, is reversible, and that its kinetics is linear.

Effect of Indobufen on Platelet Functions in Angina Patitents at Rest and During Exercise

Platelet aggregation induced by 3 concentrations of ADP and collagen was assessed in 30 patients with stable angina before and after exercise with bicyle ergometer. The patients received a single Oral 200 mg dose of indobufen and placebo according to a cross-over design in double-blind conditions. An increase in platelet sensitivity to both aggregating agents occurred when exercise was carried out after placebo, whereas indobufen markedly inhibited ADP- and collagen-induced aggregation. Circulating platelet aggregates increased in some patients during exercise after placebo but not after indobufen. In 20 patients 14C-serotonin release induced by collagen in PRP was investigated. The release was increased when placebo was administered before exercise but it was inhibited when indobufen was given before exercise. In the same patients MDA levels after thrombin-induced stimulation of platelets in PRP increased during exercise after placebo but decreased during exercise after indobufen. These results suggest that effort may be an important factor in activation of platelet functions and that the use of drugs blocking the arachidonate pathway and the release reaction may be appropriate in patients with angina.

Platelet aggregometry and anti-platelet isoantibodies

102 sera from polytransfused patients have been screened in platelet aggregometry. Anti-human platelet isoantibodies, tested against 'responsive' human platelets in PRP, give in the aggregometer a decrease in optical density recorded as a sigmoidal curve. In the first step of reaction PF3 availability suggests that the primary action of antibody is to damage the platelet membrane. The second step might be a true aggregation (an ADP-mediated platelet clumping) or a platelet lysis, depending on the type and the potency of antibody, on the type of platelets (normal or thrombasthenic) and on some experimental conditions. These conclusions, confirmed by electron microscopy findings, suggest that aggregometry is a very rapid and simple method of detecting platelet antibodies.

Human platelet aggregation by mixed cryoglobulins

Glomerulonephritis in idiopatic mixed cryoglobulinemia represents perhaps a glomerular damage by immune complexes. In this study, a sigmoidal-like curve was obtained after addition of 13 different mixed cryoglobulins to both autologous and isologous platelet-rich plasma, tested in platelet aggregometer. The lag phase of the curve corresponds to platelet phagocytosis of cryoglobulin-binding ferritin, as shown in electron microscopy and the optical density decrease phase corresponds to the aggregation of platelets that shows the same ultrastructural characteristics of ADP-induced platelet aggregation. This platelet aggregation is inhibited by different drugs. Intraglomerular platelet aggregation by cryoglobulins might play a key role in determining the glomerular damage in cryoglobulinemia by the release of nucleotides and vasoactive amines.

Anti-heparin activity of a macroglobulin from a patient with breast adenocarcinoma

We describe a case of IgM paraproteinemia, whose macroblogulin reacted anomalously with heparin. Anti-heparin activity of the paraprotein was suggested by insensibility of the patient's plasma to heparin in heparin-thrombin clotting time. Moreover, the presence of heparin in the medium markedly reduced the inhibitory effect of the paraprotein on platelet aggregation by ADP.