Prolonged inhibition of ex vivo sodium arachidonate-induced platelet aggregation and malondialdehyde (MDA) production by sulphinpyrazone (Anturan) in man

A serial study of platelet reactivity throughout the first six months after myocardial infarction: its modification by sulphinpyrazone

Platelet reactivity was studied immediately after and throughout the first 6 months following myocardial infarction. Its modification by sulphinpyrazone was observed. Out of 65 consecutive patients admitted to the coronary care unit, ten did not meet the protocol criteria. Fifty five received either placebo or sulphinpyrazone in a double-blind trial for 6 months, treatment being started within 6 days of infarction. Forty four patients completed the study (19 on placebo and 25 on sulphinpyrazone). An additional ten patients commenced treatment within one day of infarction and were studied daily for one week. Platelet hyper-reactivity was demonstrable in all patients at presentation and persisted throughout the 6 months in the control group. This effect was reversed by sulphinpyrazone, the modification of reactivity being established by the third day of treatment.

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.

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

Simultaneous evaluation of inhibition of the sodium arachidonate-induced platelet aggregation and drug disposition was studied in rabbits receiving single doses of sulfinpyrazone (SO) and its sulfide metabolite (S). The metabolism of SO was found to be interconversible with that of S. Due to the parallelism of disposition profiles, the observed concentration-related inhibition not only strongly correlated with the much more potent sulfide, but also correlated with the p-OH-sulfide (OH-S) or with a summation of two substances. Exaggeration of inhibition at 24-30 h and rebound effect at 48 h were found after the substances were administered. There may exist a circadian rhythm of platelet aggregation.

Arachidonic acid-induced platelet aggregation and prostanoid formation in whole blood in relation to plasma concentration of indomethacin

A single oral dose of indomethacin 1 mg/kg was given to 6 male and 6 female volunteers. The formation of thromboxane B2 (TXB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) in clotting whole blood was measured by radioimmunoassay, and platelet aggregation induced by arachidonic acid (AA) was measured with a plasma aggregometer. The results were related to the concomitant plasma concentration of indomethacin. The maximum plasma concentration ranged between 3.24 and 8.11 micrograms/ml and the elimination half-life between 4 and 11 h. Formation of the prostanoids was reversibly inhibited, with maximum suppression when the drug concentration in plasma exceeded 0.5-1.0 microgram/ml; the IC50 was approximately 0.1 microgram/ml. Platelet aggregation was also reversibly inhibited. The correlation between the formation of prostanoids and the different phases of the aggregatory response to exogenous AA is discussed.

Pharmacokinetics of sulphinpyrazone and its major metabolites after a single dose and during chronic treatment

The pharmacokinetics of sulphinpyrazone and its major metabolites (sulfide, sulfone, p-hydroxysulfone and p-hydroxy-sulphinpyrazone) were investigated in 9 volunteers after a single oral dose as well as after chronic treatment for 23 days. Chronic administration of sulphinpyrazone, in comparison with a single oral dose, led to significant changes in plasma AUC (115.86 to 42.90 mg/l . h), in renal clearance (1.06 to 1.80 l/h), in hepatic intrinsic clearance (319.0 to 598.0 l/h), and in the unbound fraction in plasma 1.15 to 1.69%) and in tissue (2.73 to 1.31%). The volume of distribution changed from 20.24 to 52.04 l. The steady state concentrations predicted from the single dose were significantly higher than the values found after chronic treatment. The results suggest that sulphinpyrazone induces its own metabolism. The metabolism of the sulfone, p-hydroxysulfone and the p-hydroxy-sulphinpyrazone to further degradation products was also induced. Chronic treatment with sulphinpyrazone reduced the plasma AUC of the sulfide and caused a decrease in its elimination half-life (20.9 to 14.3 h). Since considerable amounts of the sulfide are formed in the G.I. tract, it is suggested that besides the induction of metabolism, bacteria which reduce sulphinpyrazone to the sulfide may also be responsible for the observed pharmacokinetic changes.

Inhibition of human platelet cyclo-oxygenase activity by sulfinpyrazone and three of its metabolites

Sulfinpyrazone and three of its major metabolites were compared in vitro for their inhibitory effect on human platelet cyclo-oxygenase activity. Sulfinpyrazone appeared to be about 15-20 times less potent than its sulfide metabolite (G25671) and 6-7 times less potent than the other two compounds, the sulfone metabolite (G31442) and p-hydroxysulfide (G33378). All four compounds were apparently competitive inhibitors of platelet cyclo-oxygenase activity. Comparison of the potency of sulfinpyrazone and its metabolites, as determined in the present study and the plasma levels previously measured in man, indicates that sulfinpyrazone and G33378 were not potent enough to be effective in man. G31442 showed inhibitory potency slightly lower than its corresponding plasma levels, whereas G25671 was effective at concentrations well below those found in human plasma. This study supports the hypothesis that sulfinpyrazone metabolites (in particular the sulfide) rather than the drug itself affect platelet function when administered therapeutically.

Plasma levels of sulfinpyrazone and of two of its metabolites after a single dose and during the steady state

The pharmacokinetics of sulfinpyrazone, and the plasma levels of its sulfide and sulfone metabolites, have been determined after a single oral dose (400 mg) and during steady-state conditions (4 x 200 mg daily for 6 days) in healthy female volunteers. The plasma half-lives of sulfinpyrazone, the sulfone and the sulfide were 3.7, 3.2 and 14.7 h, respectively, during steady-state. After a single dose and during steady state conditions the half-lives of sulfinpyrazone and the sulfone did not differ significantly. The trough plasma levels of the sulfide metabolite exceeded those of the parent compound in four of the six volunteers on the last day of the study. The data suggest that in man the most likely candidate for the prolonged inhibition of platelet aggregation observed after treatment with sulfinpyrazone is its sulfide metabolite, because of its prolonged elimination.

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.

Sulfinpyrazone decreases epinephrine-induced platelet aggregation after myocardial infarction

Platelet studies were performed during a controlled double-blind randomized clinical trial of sulfinpyrazone (Anturane Reinfarction Trial) in 41 patients who had recent myocardial infarction. Aggregation of platelet-rich plasma by thrombin (0.185, 0.246 U/ml), collagen, adenosine diphosphate, and adrenaline (0.23, 0.46, and 0.91 microgram/ml) was estimated after a 12 hour fast including abstinence from drugs and cigarette smoking. The tests were carried out 2 weeks after myocardial infarction and 6, 12, and 24 months later. At the last visit, washed platelet suspensions were also tested for aggregation to thrombin (0.03, 0.015 U/ml) +/- epinephrine (0.55 microgram/ml) and their production of malonyldialdehyde was estimated. A significant (p less than 0.02) reduction (50%) of the aggregation response of platelet-rich plasma to epinephrine was found in the group treated with sulfinpyrazone (n = 21) as compared with the placebo group (n = 20). Also, adrenaline evoked a milder (p less than 0.01) potentiation of aggregation by thrombin of the washed platelet suspensions in the sulfinpyrazone versus the placebo group. Other assays including platelet coagulant activity were not useful in discriminating between the 2 groups. It is concluded that sulfinpyrazone (200 mg 4 times daily) normalizes the platelet response to epinephrine; a relation with the drug-reported reduction of sudden death after myocardial infarction is suggested.