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Abstract

The frequency, severity, and outcome of flutamide-induced hepatic injury were prospectively evaluated in 55 patients with prostate cancer who received 125 mg of flutamide 3 times a day (daily dose: 375 mg) combined with an agonistic analogue of luteinizing hormone-releasing hormone. In addition, we examined plasma and urine concentrations of flutamide and its major metabolites 4 weeks after the beginning of flutamide therapy, and evaluated their significance in predicting flutamide-induced hepatic dysfunction. Hepatic function could be assessed in 50 patients and hepatic dysfunction during therapy was observed in 9 patients (18%); 3 patients (6%) were classified as having moderate liver dysfunction and 6 (12%) were classified as having mild liver dysfunction. The steady-state plasma levels of flutamide and its biologic active metabolite, hydroxyflutamide (OH-Flu), were not related to hepatic dysfunction. However, the concentration of another major metabolite, 4-nitro-3-(trifluoromethyl)phenylamine (FLU-1) was considerably higher in 2 patients who developed clinically significant hepatic dysfunction. These findings suggest that clinically significant hepatic dysfunction could be induced in patients with compromised flutamide metabolism, which leads to a high concentration of FLU-1. Based on results of this study, we propose that plasma FLU-1 levels are one of the predictive factors for flutamide-induced hepatic dysfunction. This hypothesis will be confirmed in a large-scale study.

Microbial Metabolism. Part 11. Metabolites of Flutamide

“…6) Although it is suggested that flutamide and its toxic metabolites could be responsible for such hepatic injury the mechanism of toxicity remains presently unknown. 6) It is observed that the serum concentration of FLU-1 is higher 3,7) and that of OH-flutamide is lower in patients with liver dysfunction than in those with normal liver function. 11) The formation of OH-flutamide from the parent compound is catalyzed by CYP1A2.…”

“…The 1 H-NMR data showed close resemblance to those of 1 except for the presence of a two proton singlet due to an amino group at d 5.30. It was identified as 2-methyl-N-[4-amino-3-(trifloromethyl) The short names as per Aizawa et al 7) and Takashima et al 18) publications. …”

“…3) It is absorbed rapidly from the gastrointestinal track of humans and rats after oral administration and undergoes extensive metabolism in the liver [3][4][5] through hydrolysis, hydroxylation, N-acetylation and nitroreduction to yield several metabolites. 6) The major metabolites detected in plasma are 2-hydroxyflutamide (OH-FLU) and 4-nitro-3-(trifluoromethyl)phenylamine (FLU-1) 7) with concentrations higher than that of flutamide. 8) It is suggested that the antiandrogen activity of flutamide is largely associated with its main metabolite, 2-hydroxyflutamide.…”

“…Flutamide with the structure similar to that of testosterone 9) however, is a weak antiandrogen. 10) FLU-1, which is devoid of any antiandrogenic activity 7) is formed by carboxyesterase-catalysed hydrolysis. 6) It is a product of a clearance pathway.…”

“…3) However, urinary excretion is not a major pathway of flutamide elimination in humans. 7) The use of flutamide as therapeutic agent against prostrate cancers is eclipsed by rare incidences of idiosyncratic liver injury. 6) Although it is suggested that flutamide and its toxic metabolites could be responsible for such hepatic injury the mechanism of toxicity remains presently unknown.…”