Percutaneous penetration and metabolism of topical (14C)flutamide in men

Flutamide metabolism in four different species in vitro and identification of flutamide metabolites in human patient urine by high performance liquid chromatography/tandem mass spectrometry

A new metabolic scheme of flutamide is proposed in this article. Some patients treated with flutamide, a nonsteroidal antiandrogen, have developed severe hepatic dysfunction. Toxic metabolites have been proposed to be responsible for these negative effects. In this study, the qualitative aspects of the in vitro metabolism of flutamide in liver microsomes from human, dog, pig, and rat were evaluated. A direct comparison of the flutamide metabolism in liver and prostate microsomes from pig was made, and the in vivo metabolism of flutamide was investigated in urine from orally treated prostate cancer patients. Liquid chromatography/tandem mass spectrometry was used for analysis. The mass spectrometer was equipped with an electrospray interface and operated in the negative ion mode. In liver microsomes from pig, dog, and rat, extensive hydroxylation of flutamide occurred. One, two, or three hydroxy groups were attached, and isomeric forms were detected for both monohydroxylated and trihydroxylated drug. In pig liver microsomes, isomers of a third metabolite, hydroxylated 4-nitro-3-(trifluoromethyl)-aniline, were also found after incubation with either flutamide or 2-hydroxyflutamide. In human liver microsomes, the pharmacologically active 2-hydroxyflutamide was the only metabolite detected. Several phase I metabolites as well as four intact phase II metabolites could be recovered from the urine samples. For the first time in humans, glucuronic acid conjugates of hydroxylated 4-nitro-3-(trifluoromethyl)-aniline, and mono- and dihydroxylated flutamide were identified, together with hydroxylated 4-nitro-3-(trifluoromethyl)-aniline conjugated with sulfate. In addition, one mercapturic acid conjugate of hydroxylated flutamide, probably formed from flutamide via a reactive intermediate, was detected.

Fluridil, a rationally designed topical agent for androgenetic alopecia: first clinical experience

BACKGROUND

Fluridil, a novel topical antiandrogen, suppresses the human androgen receptor. While highly hydrophobic and hydrolytically degradable, it is systemically nonresorbable. In animals, fluridil demonstrated high local and general tolerance.

OBJECTIVE

To evaluate the safety and efficacy of a topical anti- androgen, fluridil, in male androgenetic alopecia.

METHODS

In 20 men, for 21 days, occlusive forearm patches with 2, 4, and 6% fluridil, isopropanol, and/or vaseline were applied. In 43 men with androgenetic alopecia (AGA), Norwood grade II-Va, 2% fluridil was evaluated in a double-blind, placebo-controlled study after 3 months clinically by phototrichograms, hematology, and blood chemistry including analysis for fluridil, and at 9 months by phototrichograms.

RESULTS

Neither fluridil nor isopropanol showed sensitization/irritation potential, unlike vaseline. In all AGA subjects, baseline anagen/telogen counts were equal. After 3 months, the average anagen percentage did not change in placebo subjects, but increased in fluridil subjects from 76% to 85%, and at 9 months to 87%. In former placebo subjects, fluridil increased the anagen percentage after 6 months from 76% to 85%. Sexual functions, libido, hematology, and blood chemistry values were normal throughout, except that at 3 months, in the spring, serum testosterone increased within the normal range equally in placebo and fluridil groups. No fluridil or its decomposition product, BP-34, was detectable in the serum at 0, 3, or 90 days.

CONCLUSION

Topical fluridil is nonirritating, nonsensitizing, nonresorbable, devoid of systemic activity, and anagen promoting after daily use in most AGA males.

Metabolism and enantioselective pharmacokinetics of Casodex in man

1. Five healthy male volunteers received a single oral dose (50 mg; 42 microCi) of 14C-Casodex, a racemic compound, which has its antiandrogen activity predominantly in R-Casodex, the (-)-enantiomer, with little activity in S-Casodex, the (+)-enantiomer. 2. Plasma concentrations of R-Casodex increased slowly in all subjects to reach a peak of 559-970 ng/ml between 15 and 48 h after dosing and, thereafter, declined monoexponentially with a mean half-life of 4.2 days. Plasma concentrations of S-Casodex rose rapidly to reach a peak of 32-66 ng/ml within the first 2-5 h, and then declined monoexponentially with a mean half-life of 19 h. Plasma concentrations of the racemate were in very good agreement with the sum of the enantiomer concentrations throughout the study and were very similar to concentrations of total radioactivity over the first 4 days. 3. About 80% of the radioactive dose was recovered in urine (35.8 +/- 1.7%; mean +/- SEM) and faeces (42.6 +/- 2.9%) during a total collection over 9 days; this incomplete recovery was consistent with the slow elimination of R-Casodex. 4. T.l.c. of urine extracts indicated extensive metabolism of Casodex to two polar metabolites identified as the glucuronide conjugates of Casodex and hydroxy-Casodex; almost no parent compound was observed. Virtually all of the Casodex glucuronide excreted in urine during the first 2 days was derived from S-Casodex, consistent with the relatively low plasma concentrations and rapid elimination of this enantiomer. 5. T.l.c. of faecal extracts showed the presence of both Casodex and hydroxy-Casodex; these may have been eliminated in bile as the glucuronide conjugates, with subsequent hydrolysis in the intestinal tract.

Metabolism of Casodex in laboratory animals

1. Casodex, a non-steroidal antiandrogen, was eliminated primarily in faeces by rat, mouse, rabbit and dog. Rat, mouse and rabbit eliminated 20-30% of a single oral dose (8-25 mg/kg) in urine; only 3-4% was excreted in urine by dog (2.5 mg/kg). Oral absorption was about 80% in rat, mouse, rabbit and dog. 2. Most of the dose was recovered in 48 h from rat, mouse and rabbit. In rat, < 1% of the dose was exhaled as 14CO2 and < 1% remained in the carcass after 7 days. Recovery from dog was incomplete in 4 days but consistent with the long plasma elimination half-life of 7-7.5 days. Casodex was eliminated from rat plasma with a half-life of 17-21 h. 3. Examination of urine indicated extensive metabolism of Casodex and showed a marked species difference. In rat, mouse and dog, Casodex was cleaved at the amide to yield a carboxylic acid and an aromatic amine which subsequently underwent ring hydroxylation with sulphate conjugation. In rabbit, the major urinary metabolite was Casodex glucuronide, conjugated on the tertiary hydroxyl. 4. The major component in faeces of all species was unchanged Casodex; some hydroxy-Casodex was also observed in rat faeces. Analysis of rat and dog bile indicated that Casodex and hydroxy-Casodex were eliminated in bile primarily as glucuronide conjugates.

Single and multiple dose pharmacokinetic evaluation of flutamide in normal geriatric volunteers

Single dose and steady-state pharmacokinetics of flutamide (F) and its active plasma metabolite, hydroxyflutamide (HF) were studied in twelve healthy geriatric volunteers administered 250 mg flutamide capsules on day 1 and 250 mg flutamide capsules three times a day on days 2 through 9. After oral administration, F was rapidly absorbed and metabolized. It was present in the plasma in small and variable concentrations, which precluded quantitative assessment of pharmacokinetic parameters for individual subjects. Steady-state plasma concentrations were reached on or before Day 6. The mean steady state Cmax (Day 9), 112.7 ng/ml, occurred at 1.3 hr. Pharmacokinetic analysis of mean data at steady-state gave a distribution and elimination half-life of 0.8 hr and 7.8 hours, respectively. The plasma levels for HF were much higher and less variable than F. The mean Cmax for HF averaged 894 ng/ml at 2.7 hours after a single dose and 1719 ng/ml (Day 9) at 1.9 hr after multiple doses. The distribution and elimination half-lives of HF at steady-state were 1.9 and 9.6 hours, respectively. The steady-state HF plasma concentrations were also achieved on or before Day 6 and were approximately twice those obtained after a single dose. From this study, it has been demonstrated that the pharmacokinetics of F and HF do not change appreciably upon multiple dosing of 250 mg F capsule given three times a day.

Metabolism of steroid-modifying anticancer agents

The application of steroid-modifying drugs as a strategy for the treatment of hormone-dependent cancers has gained increasing popularity during the past decade. However, it is important to point out and emphasize that very few of the agents were originally designed for their current application. Most were designed for other purposes, predominantly fertility control (e.g. LHRH agonists and the antiestrogens). Nevertheless, now it is possible to integrate their actions to design rational therapies. There are many reasons for the current interest in antisteroidal drugs. The initial euphoria over the potential ability of combination chemotherapy to cure breast and prostatic carcinoma has proved to be premature. Combination chemotherapy has many severe side-effects which limits patient acceptability, especially if the patient realizes that the likelihood of a cure is remote. In the main, antisteroidal therapies do not have many side-effects and those that do, e.g. aminoglutethimide, are the focus of increased efforts in drug design to produce increased drug specificity. Finally, there is a growing realization that hormone-dependent cancer control with a nontoxic, antisteroidal therapy may be the most acceptable approach currently available for early disease management. Chemotherapy would then be reserved as the final option for treatment. The description of drug metabolism has been central to the development of synthetic LHRH analogs and an understanding of the mode of action of nonsteroidal antiestrogens and antiandrogens. The discovery of steroid synthetic pathways has been essential for the development of the aromatase inhibitors. This whole area of endeavor has now become a major focus of attention for the medicinal chemist. A new generation of agents is entering clinical evaluation which will provide a wealth of valuable information about the successful (or unsuccessful?) methods to control hormone-dependent disease. Since the success or failure of a drug can often depend upon formulation, pharmacokinetics, bioavailability or metabolism, it is our hope that this overview might help solve some of the future problems.