Single doses of indoprofen 100 mg and lonazolac-Ca 200 mg were given orally to eight healthy volunteers. Blood samples were taken prior to and at various times until 24 hours after the dose. Drug concentrations in plasma were analyzed by HPLC and thromboxane B2 (TXB2) in serum by radioimmunoassay. Platelet aggregation in plasma was induced by various concentrations of arachidonic acid and evaluated with respect to different phases in the aggregatory response. The drugs were rapidly absorbed and for both compounds the decline in plasma concentrations described two phases. Although concentrations of indoprofen were up to ten times higher than those of lonazolac, the two drugs were almost equally potent inhibitors of generation of TXB2, with IC50 for indoprofen of 1.4-1.5 X 10(-7) M and for lonazolac 2.1-3.0 X 10(-7) M. Their effects on the lag phase in platelet aggregation paralleled the inhibition of TXB2 formation. However, the rate and extent of aggregation were more inhibited by indoprofen than by lonazolac, and the discrepancy was greater than would be expected from concomitant values for TXB2 suppression. The rate of aggregation appeared to be the most sensitive variable, since the extent of aggregation followed an all-or-none pattern. The present results show that the concentrations reached after clinically used doses of antiinflammatory drugs may vary widely in relation to the concentrations needed for maximum inhibition of platelet cyclooxygenase. The results from aggregation tests may support the idea that non-steroid antiinflammatory drugs can differ in their mechanisms of action.

Compared effects of the two antiinflammatory drugs indoprofen and lonazolac on thromboxane generation and on platelet aggregation, related to plasma concentrations after single oral doses

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-ketoprostaglandin F1α (6-keto-PGF1α) in clotting whole blood was measured by radioimmunoassay, and platelet aggregation induced by archidonic 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 µg/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 µg/ml; the IC50 was approximately 0.1 µg/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.

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

The effect of thromboxane A2 synthesis inhibitors on platelet aggregation in whole blood.

Fenflumizole is a substituted triaryl-imidazole with anti-inflammatory activity. Its disposition in man was studied after single intravenous and oral doses to 8 healthy male volunteers. Formation of the prostanoids thromboxane B2 (TXB2) and 6-keto-prostaglandin F1 alpha (6-k-PGF1 alpha) in clotting blood was studied concomitantly. The pharmacokinetics after intravenous doses (0.1 mg/kg) could be fitted to a three compartment model and the half-lives (t 1/2) corresponding to the three phases were 2 min., 1 hour and 15 hours, respectively. The volume of distribution was 386 l and the plasma clearance 0.5 l per min. Oral doses (0.5 mg/kg) were rapidly absorbed (t 1/2 = 0.2 hr) and the following elimination from plasma had two phases with half-lives of 1 hour and 14 hours. Bioavailability was 50% due to a pronounced first-pass effect. The two metabolites mono- and didemethylfenflumizole were detected after both oral and intravenous doses and their maximum plasma concentrations occurred after 1-2 hours irrespective of the administration route. A concentration dependent depression of prostanoid formation was seen, the IC50 for TXB2 and 6-k-PGF1 alpha being 19 and 53 ng/ml respectively.

Single intravenous and oral doses of fenflumizole: pharmacokinetics and effects on prostanoid formation.

Effects of a new anti-inflammatory imidazole derivative, fenflumizole, on platelet aggregation in the rabbit

Fenflumizole (2-(2,4-difluorophenyl)-4,5-bis(4-methoxyphenyl)imidazole), a new non-steroidal anti-inflammatory drug, was given to healthy subjects in single oral doses of 0.1, 1 and 2 mg/kg. The effect of the drug was followed for up to 8 h by repeated tests of arachidonic acid-induced platelet aggregation and was related to its concomitant plasma concentration. Fenflumizole reversibly inhibited platelet aggregation and the degree of inhibition was found to be linearly correlated with the log plasma concentration. There was depression of the formation of thromboxane B2 and 6-keto-prostaglandin F1α (the stable metabolites of thromboxane A2 and prostacyclin) in clotted whole blood measured by radioimmunoassay after fenflumizole 1 mg/kg. This effect was directly related to the concentration of the drug in plasma, the maximum effect being reached at fenflumizole concentrations >200 ng/ml. EC50-values for inhibition of the formation of thromboxane B2 and 6-keto-prostaglandin 
$$F_{1\alpha } $$

 were approximately 20 and 40 ng/ml, respectively. The results suggest that orally administered fenflumizole is a potent inhibitor of platelet aggregation and prostanoid formation.

Effects of fenflumizole on aggregation ex vivo of human platelets and formation of thromboxane B2 and 6-keto-prostaglandin-F1 alpha.

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Effects of fenflumizole on aggregation ex vivo of human platelets and formation of thromboxane B2 and 6-keto-prostaglandin-F1 alpha.