Binding of sulfinpyrazone and its metabolites in human serum and in solutions of human serum albumin

Correlation between inhibitory effect on platelet aggregation and disposition of sulfinpyrazone and its metabolites in rabbits. Part II: Multiple dose study

In a crossover study rabbits were given perorally sulfinpyrazone (SO) and the sulfide metabolite (S) every 24 h for 5 days on separate occasions and inhibition of aggregation was measured. The results showed: the dosage regimen is effective if the minimum effective concentration of S is defined to be between 0.5-1.0 microgram ml-1, and the repeated dosing did not cause changes in disposition kinetics except that the terminal half-life of S was reduced after dosing with S. No significant accumulations in trough concentration and inhibition of aggregation were observed. The results obtained in this study could provide some useful information for design of dosage regimen and blood level monitoring for humans.

Renal clearance of sulphinpyrazone in man

Six healthy young volunteers received a single dose of sulphinpyrazone 200 mg p.o. Plasma concentration and urinary excretion rate curves showed large intersubject variation for sulphinpyrazone and its metabolites. The sulphide metabolite could only be detected in plasma and not before 3-7 h after ingestion. The total recovery in urine of all compounds varied from 30-56% of the dose. In two subjects the mean residence time of sulphinpyrazone was twice as long as in the other subjects (10.4 h compared with 4.6 h), but the area under the plasma concentration-time curve was comparable to that in the others (mean: 3.0 mg X ml-1 X min), indicating that drug absorption was quantitatively similar but delayed. The renal clearance of sulphinpyrazone varied from 14-40 ml X min-1 (mean: 28 ml X min-1). In view of the very high plasma protein binding of sulphinpyrazone, active tubular secretion is the predominant mechanism in its renal clearance. The same holds for the sulphone metabolite, which has a mean renal clearance of 24 ml X min-1, and even more for the p-hydroxysulphinpyrazone metabolite, which has a renal clearance of 118 ml X min-1. No unambiguous evidence was found in favour of concentration-dependent renal clearance of sulphinpyrazone or its metabolites over the concentration range studied. The renal clearance, especially of sulphinpyrazone, appeared to be dependent on urine pH and not on urine flow rate.

Mechanisms of action of sulphinpyrazone

Sulphinpyrazone normalises the shortened platelet survival associated with gout or artificial heart valves and has shown benefit in secondary prevention of myocardial infarction. The compound is metabolised in all species but in variable amounts to a sulphide metabolite which is a potent cyclo-oxygenase inhibitor. At the plasma concentration found in man, the metabolic inhibits prostaglandin synthesis-dependent platelet behaviour and this is therefore the likely mechanism of action of sulphinpyrazone. The compound has some additional effects which may be important.