On the pharmacokinetics of fenflumizole, a novel antiinflammatory agent, after single oral administration to healthy subjects

Antiplatelet effects of fenflumizole, a new anti-inflammatory drug, in dogs

Fenflumizole (2-(2,4-difluorophenyl)-4,5-bis(4-methoxyphenyl) imidazole) was given to dogs in a single oral dose of 3 or 10 mg/kg. The plasma concentrations of fenflumizole and the two metabolites (mono- and di-demethyl forms) attained to the peak level 1-2 hr after dosing of fenflumizole, returning to near the predose levels 8 hr after the dosing. Fenflumizole (10 mg/kg) given orally significantly inhibited collagen- and ADP-induced platelet aggregations ex vivo over 4 hr after the dosing. Fenflumizole effectively inhibited in vitro collagen-induced platelet aggregation, but failed to prevent ADP-induced aggregation. The mono-demethyl form of fenflumizole inhibited in vitro ADP- and collagen-induced aggregations, but the di-demethyl form was ineffective in inhibiting them.

Pharmacokinetics of 14C-fenflumizole after intravenous administration to man

The disposition of 14C-labelled fenflumizole was studied in five healthy subjects who received 0.1 mg/kg of fenflumizole as single intravenous doses. Radioactivity was measured in whole blood, plasma, urine and feces from prior to until 168 hours after dose administration. Chemical determinations of fenflumizole and its two demethylated derivatives in plasma were made by HPLC followed by fluorescence detection. Concentrations of fenflumizole calculated from radioactivity in plasma were consistently higher than from chemical determinations, suggesting the presence of metabolites. Radioactivity in blood cells decreased more slowly than in plasma. Plasma concentrations versus time could be described by a four-compartment model, with a terminal half-life of 119 hours (median). About 50% of the dose was excreted with the faeces, and about 4% was recovered in the urine. Unchanged fenflumizole in the urine accounted for 0.0001% of the total dose. Renal clearance of radioactive material decreased at low concentrations of radioactive compound in plasma, which may indicate changes in unbound fraction of drug and metabolites, or a saturable tubular reabsorption process. The slow elimination of fenflumizole is consistent with slow release from tissues and/or enterohepatic recycling.

A double-blind placebo-controlled evaluation of fenflumizole in rheumatoid arthritis

Twenty-eight patients with active classical or definite rheumatoid arthritis were randomly allocated to treatment with fenflumizole 200 mg or 100 mg or placebo daily in a 2-week double-blind placebo-controlled study. Three patients dropped out and 25 patients completed the study. Ten patients received fenflumizole 100 mg daily, 7 patients received fenflumizole 200 mg daily and 8 patients received placebo. Clinical and laboratory assessments before and during the study revealed that in patients treated with fenflumizole, grip strength, morning stiffness and walking time improved significantly. No improvement could be seen in the placebo group. No side effects attributable to fenflumizole were observed during the study.

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

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.

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

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 F1 alpha (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 greater than 200 ng/ml. EC50-values for inhibition of the formation of thromboxane B2 and 6-keto-prostaglandin F1 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.