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Mechanism of Action
Endogenous androgens, including testosterone and dihydrotestosterone (DHT), are responsible for the normal growth and development of the male sex organs and for maintenance of secondary sex characteristics. These effects include the growth and maturation of prostate, seminal vesicles, penis and scrotum; the development of male hair distribution, such as facial, pubic, chest and axillary hair; laryngeal enlargement; vocal cord thickening; and alterations in body musculature and fat distribution. Testosterone and DHT are necessary for the normal development of secondary sex characteristics. Male hypogonadism results from insufficient secretion of testosterone and is characterized by low serum testosterone concentrations. Signs/symptoms associated with male hypogonadism include erectile dysfunction and decreased sexual desire, fatigue and loss of energy, mood depression, regression of secondary sexual characteristics, and osteoporosis.
Male hypogonadism has two main etiologies. Primary hypogonadism is caused by defects of the gonads, such as Klinefelter Syndrome or Leydig cell aplasia, whereas secondary hypogonadism is the failure of the hypothalamus (or pituitary) to produce sufficient gonadotropins (FSH, LH).
No specific pharmacodynamic studies were conducted using ANDRODERM.
ANDRODERM delivers physiologic amounts of testosterone, producing circulating testosterone concentrations that approximate the normal concentration range (300 – 1030 ng/dL) seen in healthy men. ANDRODERM provides a continuous daily dose of testosterone in a self-contained transdermal system. Following ANDRODERM application, testosterone is continuously absorbed during the 24-hour dosing period with a median (range) Tmax of 8 (4-12) hours.
In a group of 34 hypogonadal men, application of two ANDRODERM 2.5 mg/day systems to the different application sites (abdomen, back, thighs, or upper arms) delivered approximately 4 to 5 mgs of testosterone over 24 hours.
Circulating testosterone is primarily bound in the serum to sex hormone-binding globulin (SHBG) and albumin. Approximately 40% of testosterone in plasma is bound to SHBG, 2% remains unbound (free) and the rest is bound to albumin and other proteins.
Testosterone is metabolized to various 17-keto steroids through two different pathways. The major active metabolites of testosterone are estradiol and dihydrotestosterone (DHT).
During steady-state pharmacokinetic studies in hypogonadal men treated with ANDRODERM, the average DHT:T and E2:T ratios were approximately 1:10 and 1:200, respectively.
There is considerable variation in the half-life of testosterone as reported in the literature, ranging from 10 to 100 minutes. About 90% of a dose of testosterone given intramuscularly is excreted in the urine as glucuronic and sulfuric acid conjugates of testosterone and its metabolites; about 6% of a dose is excreted in the feces, mostly in the unconjugated form. Inactivation of testosterone occurs primarily in the liver.
Upon removal of the ANDRODERM systems, serum testosterone concentrations decrease with an apparent half-life of approximately 70 minutes. Hypogonadal concentrations are reached within 24 hours following system removal. There is no accumulation of testosterone during continuous treatment.
Effect of Showering
In a two-way crossover study, the effects of showering on the pharmacokinetics of total testosterone following a single application of ANDRODERM 4 mg/day were assessed in 16 hypogonadal males. Showering 3 hours after application of ANDRODERM increased Cavg by 0.5% and decreased Cmax by 0.4% respectively, as compared to not showering. The systemic exposure to ANDRODERM was similar following applications with or without showering 3 hours after application.
ANDRODERM 2 mg/day and 4 mg/day were studied in a trial designed to evaluate the use and titration of 2 mg/day and 4 mg/day systems in a clinic setting of 40 men with hypogonadism. Thirty-eight of the 40 subjects (95%) who were enrolled into the study were white and 2 subjects were African American. Ten (25%) subjects were Hispanic and 30 (75%) were Non-Hispanic. Men were between 34 and 76 years of age (mean: 55 years). Patients had previously been on stable therapy of ANDRODERM 5 mg; Androgel®2.5 g, 5 g, 7.5 g or 10 g; or Testim®2.5 g or 5 g daily before switching to ANDRODERM 4 mg/day.
Patients applied an ANDRODERM 4 mg/day system around 10 p.m. once daily for 14 days, and then were titrated up to 6 mg/day or down to 2 mg/day according to a morning serum testosterone concentration obtained at 6 a.m. on Day 8. Out of 36 patients who entered the study, 31 (86%) patients remained on the 4 mg/day dose, 4 (11%) were titrated downward to 2 mg/day, and 1 (3%) was titrated upward to 6 mg/day based on the Day 8 testosterone concentrations. The one patient that was titrated to 6 mg/day discontinued from the study for a non-safety related reason. Of the patients who were receiving ANDRODERM 5 mg/day prior to study entry (n = 11), 10 remained at 4 mg/day after titration, and 1 was titrated down to the 2 mg/day dose.
After a total of 28 days of therapy, 34 of the 35 subjects (97%) had serum testosterone Cavg within the normal range during the dosing period, with the lower bound of the 95% confidence interval for this estimate being 85% (Table 3). One subject who received ANDRODERM 4 mg/day treatment had serum testosterone Cavg below 300 ng/dL and none had Cavg concentrations above 1030 ng/dL. The mean (SD) serum testosterone Cmax following treatment with the 2 mg/day (N = 4) and 4 mg/day (N = 31) systems was 648 (145) ng/dL and 696 (158) ng/dL, respectively. Table 3 summarizes testosterone Cavg categories by treatment.
Table 3: Testosterone Cavg Categories on Day 28 after One Titration
on Day 15
|Cavg Category||Current Testosterone User
N = 35
|300 - 1030 ng/dL (n (%) (95% CI))||34/35 (97%) (85%, 100%)|
|< 300 ng/dL (n (%))||1/35 (3%)|
Figure 2 summarizes the pharmacokinetic profiles of total testosterone in 35 patients completing 28 days of ANDRODERM treatment applied as a starting dose of 4 mg/day for the initial 14 days followed by a possible dose titration.
Figure 2: Mean (SD) Steady-State Serum
Total Testosterone Concentration (ng/dL) on Day 28
In separate clinical studies using the ANDRODERM 2.5 mg/day system, 1% used 2.5 mg daily, 93% of patients used 5 mg daily, and 6% used 7.5 mg daily. The hormonal effects of ANDRODERM 2.5 mg/day system as a treatment for male hypogonadism was demonstrated in four open-label trials that included 94 hypogonadal men, ages 15 to 65 years. In these trials, ANDRODERM produced average morning serum testosterone concentrations within the normal reference range in 92% of patients.
Last reviewed on RxList: 5/14/2012
This monograph has been modified to include the generic and brand name in many instances.
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