text: Flutamide is an arylpropionamide analog with pure antiandrogenic properties, seen in figure 4. It is completely absorbed from the gastrointestinal tract after oral administration and undergoes extensive first pass metabolism to its active form, 2-hydroxyflutamide, and hydrolysis product, 3-trifluoromethyl-4-nitroaniline. Hydroxyflutamide is a more potent AR antagonist than flutamide in vivo, with higher binding affinity for the AR. Hydroxyflutamide has an elimination half-life of about 8 hours in humans. Hydrolysis of the amide bond represents the major metabolic pathway for this active metabolite. By reversing the stimulatory effect of DHT on ventral prostate weight, flutamide is approximately 2-fold more potent than cyproterone acetate. Hydroxyflutamide has relatively low binding affinity to AR and is therefore generally used at  high doses in order to achieve complete AR blockage in therapy.