Oral nafazatrom in man: effect on inhaled antigen challenge.

The effect of oral nafazatrom (Bay g6575, 2 X 3 g) or placebo on inhaled antigen challenge was assessed in a double-blind study. In four subjects antigen challenge resulted in an immediate fall of 93.2 +/- 3.36% in airflow at 40% of vital capacity (Vp40) and a 45.85 +/- 4.95% reduction in forced partial expiratory volume at one second (FEV1). Neither nafazatrom nor placebo had any effect on baseline lung function or that after challenge. Leukotriene B4 was generated by ex vivo stimulus of blood with ionophore A23187, and quantified by high performance liquid chromatography (h.p.l.c.)-radioimmunoassay. No inhibition of LTB4 formation occurred ex vivo following oral nafazatrom, although addition of 10(-5) M nafazatrom to blood in vitro significantly inhibited LTB4 release. Peak plasma nafazatrom levels during the study ranged from 3.3 X 10(-7) M to 1.47 X 10(-6) M which are below the concentration (10(-5) M) at which significant 5-lipoxygenase inhibition occurs in vitro. Oral nafazatrom is ineffective as a 5-lipoxygenase inhibitor in man, probably because of poor bioavailability after administration.