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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 the maintenance of secondary sex characteristics. These effects include the growth and maturation of the 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, 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 production of testosterone and is characterized by low serum testosterone concentrations. 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 can present as primary hypogonadism caused by defects of the gonads, such as Klinefelter's Syndrome or Leydig cell aplasia while secondary hypogonadism is the failure of the hypothalamus or pituitary to produce sufficient gonadotropins (FSH, LH).
No specific pharmacodynamic studies were conducted using FORTESTA.
FORTESTA delivers physiologic amounts of testosterone, producing serum testosterone concentrations that approximate normal concentrations ( > 300 ng/dL) seen in healthy men.
FORTESTA provides continuous transdermal delivery of testosterone for 24 hours following a single application to clean, dry, intact skin of the front and inner thighs (Figure 1).
Figure 1: Mean (±SD) Serum Total Testosterone
Concentrations on Day 7 in Patients Following FORTESTA Once- Daily Application
of 40 mg of Testosterone (N=12)
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 loosely 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 DHT.
There is considerable variation in the half-life of testosterone concentration 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 acid and sulfuric acid conjugates of testosterone and its metabolites. About 6% is excreted in the feces, mostly in the unconjugated form. Inactivation of testosterone occurs primarily in the liver.
Potential for testosterone transfer
The potential for testosterone transfer from healthy males dosed with FORTESTA to healthy females was evaluated in a placebo-controlled, three-way crossover study. The washout period was approximately 29 days. Six males were treated with either FORTESTA (30 mg testosterone) or placebo to one thigh only. At 2 hours after the application of FORTESTA to males, the females rubbed their forearms for 15 minutes on the thigh of the males. Serum concentrations of testosterone were monitored in females for 24 hours after the transfer procedure. When direct skin-to-skin transfer occurred with FORTESTA mean Cavg increased by 134% and mean Cmax increased by 191%, compared to direct skin-to-skin transfer with placebo. When transfer occurred with FORTESTA while covering a thigh with boxer shorts, mean Cavg decreased by 3% and mean Cmax increased by 2%, compared to direct skin-to-skin transfer with placebo [see DOSAGE AND ADMINISTRATION].
Effect of showering
In a two-way crossover study, the effects of showering on the pharmacokinetics of total testosterone following application of FORTESTA (30 mg testosterone to each thigh; total 60 mg testosterone) were assessed in 7 hypogonadal males. There were two 7-day treatment phases, with showering 2 hours post FORTESTA application, and without showering on Day 7 of each treatment phase. Showering decreased Cavg by 3% and it increased Cmax by 13% [see DOSAGE AND ADMINISTRATION].
Clinical Study in Hypogonadal Males
FORTESTA was evaluated in a multicenter, 90 day open-label, non-comparative trial of 149 hypogonadal males with body mass index (BMI) ≥ 22 kg/m² and < 35 kg/m² and 18-75 years of age (mean age 54.5 years). The patients were screened for a single serum total testosterone concentration < 250 ng/dL, or two consecutive serum total testosterone concentrations < 300 ng/dL. Patients were Caucasian (80.5%), Black (10.1%), Hispanic (7.4%) and other (2.0%).
FORTESTA was applied once each morning to the thighs at a starting dose of 40 mg of testosterone (4 pump actuations) per day. The dose was adjusted between a minimum of 10 mg and a maximum of 70 mg testosterone on the basis of total serum testosterone concentration obtained 2 hours post FORTESTA application on Days 14, 35, and 60 (± 3 days).
The primary endpoint was the percentage of patients with Cavg within the normal range (greater than or equal to 300 ng/dL and less than or equal to 1140 ng/dL) on Day 90. In patients treated with FORTESTA, 77.5% (100/129) had Cavg within the normal range on Day 90. The secondary endpoint was the percentage of patients with Cmax above three pre-determined limits. The percentages of patients with Cmax greater than 1500 ng/dL, and between 1800 and 2499 ng/dL on Day 90 were 5.4% and 1.6%, respectively. No patient had a Cmax greater than or equal to 2500 ng/dL on Day 90.
Dose titrations on Days 14, 35 and 60 resulted in mean (SD) Cavg and Cmax for final doses of 10 mg – 70 mg on Day 90 shown in Table 5.
Table 5 : Mean (±SD) Steady-State Testosterone
Concentrations (Cavg and Cmax) by final dose on Day 90
Figure 2 summarizes the pharmacokinetic profiles of total testosterone in patients completing 90 days of FORTESTA treatment administered as 40 mg of testosterone once-daily for the initial 14 days followed by possible titration according to follow-up testosterone measurements.
Figure 2 : Mean (±SD) Steady-State Serum Total Testosterone
Concentrations on Day 90 (N=129)
Additionally, there were no clinically significant changes from baseline for sex hormone binding globulin (SHBG) (slight decrease), E2 (slight increase) and ratio of DHT to total testosterone (slight increase) at Day 90.
Last reviewed on RxList: 9/23/2013
This monograph has been modified to include the generic and brand name in many instances.
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