Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

12.2 Pharmacodynamics
In man, a single 5-mg oral dose of PRO-CURE produces a rapid reduction in serum DHT concentration, with the maximum effect observed 8 hours after the first dose. The suppression of DHT is maintained throughout the 24-hour dosing interval and with continued treatment. Daily dosing of PRO- CURE at 5 mg/day for up to 4 years has been shown to reduce the serum DHT concentration by approximately 70%. The median circulating level of testosterone increased by approximately 10-20% but remained within the physiologic range. In a separate study in healthy men treated with finasteride 1 mg per day (n=82) or placebo (n=69), mean circulating levels of testosterone and estradiol were increased by approximately 15% as compared to baseline, but these remained within the physiologic range.
In patients receiving PRO-CURE 5 mg/day, increases of about 10% were observed in luteinizing hormone (LH) and follicle-stimulating hormone (FSH), but levels remained within the normal range. In healthy volunteers, treatment with PRO-CURE did not alter the response of LH and FSH to gonadotropin- releasing hormone indicating that the hypothalamic-pituitary-testicular axis was not affected.

In patients with BPH, PRO-CURE has no effect on circulating levels of cortisol, prolactin, thyroid- stimulating hormone, or thyroxine. No clinically meaningful effect was observed on the plasma lipid profile (i.e., total cholesterol, low density lipoproteins, high density lipoproteins and triglycerides) or bone mineral density.
Adult males with genetically inherited Type II 5α-reductase deficiency also have decreased levels of DHT. Except for the associated urogenital defects present at birth, no other clinical abnormalities related to Type II 5α-reductase deficiency have been observed in these individuals. These individuals have a small prostate gland throughout life and do not develop BPH.
In patients with BPH treated with finasteride (1-100 mg/day) for 7-10 days prior to prostatectomy, an approximate 80% lower DHT content was measured in prostatic tissue removed at surgery, compared to placebo; testosterone tissue concentration was increased up to 10 times over pretreatment levels, relative to placebo. Intraprostatic content of PSA was also decreased.
In healthy male volunteers treated with PRO-CURE for 14 days, discontinuation of therapy resulted in a return of DHT levels to pretreatment levels in approximately 2 weeks. In patients treated for three months, prostate volume, which declined by approximately 20%, returned to close to baseline value after approximately three months of discontinuation of therapy.

Pharmacokinetic Properties

12.3      Pharmacokinetics
Absorption
In a study of 15 healthy young subjects, the mean bioavailability of finasteride 5-mg tablets was 63% (range 34-108%), based on the ratio of area under the curve (AUC) relative to an intravenous (IV) reference dose. Maximum finasteride plasma concentration averaged 37 ng/mL (range, 27-49 ng/mL) and was reached 1-2 hours postdose. Bioavailability of finasteride was not affected by food.
Distribution
Mean steady-state volume of distribution was 76 liters (range, 44-96 liters). Approximately 90% of circulating finasteride is bound to plasma proteins. There is a slow accumulation phase for finasteride after multiple dosing. After dosing with 5 mg/day of finasteride for 17 days, plasma concentrations of finasteride were 47 and 54% higher than after the first dose in men 45-60 years old (n=12) and 70 years old (n=12), respectively. Mean trough concentrations after 17 days of dosing were 6.2 ng/mL (range, 2.4- 9.8 ng/mL) and 8.1 ng/mL (range, 1.8-19.7 ng/mL), respectively, in the two age groups. Although steady state was not reached in this study, mean trough plasma concentration in another study in patients with BPH (mean age, 65 years) receiving 5 mg/day was 9.4 ng/mL (range, 7.1-13.3 ng/mL; n=22) after over a year of dosing.
Finasteride has been shown to cross the blood brain barrier but does not appear to distribute preferentially to the CSF.
In 2 studies of healthy subjects (n=69) receiving PRO-CURE 5 mg/day for 6-24 weeks, finasteride concentrations in semen ranged from undetectable (<0.1 ng/mL) to 10.54 ng/mL. In an earlier study using a less sensitive assay, finasteride concentrations in the semen of 16 subjects receiving PRO-CURE 5 mg/day ranged from undetectable (<1.0 ng/mL) to 21 ng/mL. Thus, based on a 5-mL ejaculate volume, the amount of finasteride in semen was estimated to be 50- to 100-fold less than the dose of finasteride (5 g) that had no effect on circulating DHT levels in men [see also Use in Specific Populations (8.1)].
Metabolism
Finasteride is extensively metabolized in the liver, primarily via the cytochrome P450 3A4 enzyme subfamily. Two metabolites, the t-butyl side chain monohydroxylated and monocarboxylic acid metabolites, have been identified that possess no more than 20% of the 5-reductase inhibitory activity of finasteride.
Excretion
In healthy young subjects (n=15), mean plasma clearance of finasteride was 165 mL/min (range, 70- 279 mL/min) and mean elimination half-life in plasma was 6 hours (range, 3-16 hours). Following an oral dose of 14C-finasteride in man (n=6), a mean of 39% (range, 32-46%) of the dose was excreted in the urine in the form of metabolites; 57% (range, 51-64%) was excreted in the feces.
The mean terminal half-life of finasteride in subjects 70 years of age was approximately 8 hours (range, 6-15 hours; n=12), compared with 6 hours (range, 4-12 hours; n=12) in subjects 45-60 years of age. As a result, mean AUC(0-24 hr) after 17 days of dosing was 15% higher in subjects 70 years of age than in subjects 45-60 years of age (p=0.02).


Table 3
Mean (SD) Pharmacokinetic Parameters in Healthy Young Subjects (n=15)
Mean (± SD)
Bioavailability                          63% (34-108%)*
Clearance (mL/min)                            165 (55)
Volume of Distribution (L)                     76 (14)
Half-Life (hours)                             6.2 (2.1)
*Range
Pediatric
Finasteride pharmacokinetics have not been investigated in patients <18 years of age.
Finasteride is not indicated for use in pediatric patients [see Warnings and Precautions (5.4), Use in Specific Populations (8.4)].
Gender
Finasteride is not indicated for use in women [see Contraindications (4), Warnings and Precautions (5.3 and 5.4), Use in Specific Populations (8.1), How Supplied/Storage and Handling (16) and Patient Counseling Information (17.2)].
Geriatric
No dosage adjustment is necessary in the elderly. Although the elimination rate of finasteride is decreased in the elderly, these findings are of no clinical significance. [See Clinical Pharmacology (12.3) and Use in Specific Populations (8.5).]

Table 4
Mean (SD) Noncompartmental Pharmacokinetic Parameters After Multiple Doses of 5 mg/day in Older Men
Mean (± SD)
45-60 years old (n=12)          70 years old (n=12)
AUC (ng•hr/mL)                                 389 (98)                     463 (186) Peak Concentration (ng/mL)                    46.2 (8.7)                   48.4 (14.7) Time to Peak (hours)                           1.8 (0.7)                     1.8 (0.6) Half-Life (hours)*                             6.0 (1.5)                     8.2 (2.5) *First-dose values; all other parameters are last-dose values

Race
The effect of race on finasteride pharmacokinetics has not been studied.
Hepatic Impairment
The effect of hepatic impairment on finasteride pharmacokinetics has not been studied. Caution should be exercised in the administration of PRO-CURE in those patients with liver function abnormalities, as finasteride is metabolized extensively in the liver.
Renal Impairment
No dosage adjustment is necessary in patients with renal impairment. In patients with chronic renal impairment, with creatinine clearances ranging from 9.0 to 55 mL/min, AUC, maximum plasma concentration, half-life, and protein binding after a single dose of 14C-finasteride were similar to values obtained in healthy volunteers. Urinary excretion of metabolites was decreased in patients with renal impairment. This decrease was associated with an increase in fecal excretion of metabolites. Plasma concentrations of metabolites were significantly higher in patients with renal impairment (based on a 60% increase in total radioactivity AUC). However, finasteride has been well tolerated in BPH patients with normal renal function receiving up to 80 mg/day for 12 weeks, where exposure of these patients to metabolites would presumably be much greater.