CLINICAL PHARMACOLOGY
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
chord thickening; and alterations in body musculature and fat distribution.
Testosterone and DHT are necessary for the normal development of secondary sex
characteristics.
Male hypogonadism, a clinical
syndrome resulting from insufficient secretion of testosterone, has two main
etiologies. Primary hypogonadism is caused by defects of the gonads, such as Klinefelter's
syndrome or Leydig cell aplasia, whereas secondary hypogonadism is the failure
of the hypothalamus (or pituitary) to produce sufficient gonadotropins (FSH,
LH).
Pharmacodynamics
No specific pharmacodynamic
studies were conducted using AndroGel 1.62%.
Pharmacokinetics
Absorption
AndroGel 1.62% delivers
physiologic amounts of testosterone, producing circulating testosterone
concentrations that approximate normal levels (300 – 1000 ng/dL) seen in
healthy men. AndroGel 1.62% provides continuous transdermal delivery of
testosterone for 24 hours following once daily application to clean, dry,
intact skin of the shoulders and upper arms. Average serum testosterone
concentrations over 24 hours (Cavg) observed when AndroGel 1.62% was applied to
the upper arms/shoulders were comparable to average serum testosterone concentrations
(Cavg) when AndroGel 1.62% was applied using a rotation method utilizing the abdomen
and upper arms/shoulders. The rotation of abdomen and upper arms/shoulders was
a method used in the pivotal clinical trial [see Clinical Studies].
Figure 2: Mean (±SD) Serum
Total Testosterone Concentrations on Day 7 in Patients Following AndroGel 1.62%
Once-Daily Application of 81 mg of Testosterone (N=33) for 7 Days
Distribution
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.
Metabolism
Testosterone is metabolized to
various 17-keto steroids through two different pathways. The major active
metabolites of testosterone are estradiol and DHT.
Excretion
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% of a dose is excreted in the feces, mostly in the
unconjugated form. Inactivation of testosterone occurs primarily in the liver.
When AndroGel 1.62% treatment
is discontinued, serum testosterone concentrations return to approximately
baseline concentrations within 48-72 hours after administration of the last
dose.
Potential for Testosterone
Transfer
The potential for testosterone
transfer following administration of AndroGel 1.62% when it was applied only to
upper arms/shoulders was evaluated in two clinical studies of males dosed with AndroGel
1.62% and their untreated female partners. In one study, 8 male subjects
applied a single dose of AndroGel 1.62% 81 mg to their shoulders and upper
arms. Two (2) hours after application, female subjects rubbed their hands,
wrists, arms, and shoulders to the application site of the male subjects for 15
minutes. Serum concentrations of testosterone were monitored in female subjects
for 24 hours after contact occurred. After direct skin-to-skin contact with the
site of application, mean testosterone Cavg and Cmax in female subjects
increased by 280% and 267%, respectively, compared to mean baseline
testosterone concentrations. In a second study evaluating transfer of
testosterone, 12 male subjects applied a single dose of AndroGel 1.62% 81 mg to
their shoulders and upper arms. Two (2) hours after application, female
subjects rubbed their hands, wrists, arms, and shoulders to the application
site of the male subjects for 15 minutes while the site of application was
covered by a t-shirt. When a t-shirt was used to cover the site of application,
mean testosterone Cavg and Cmax in female subjects increased by 6% and 11%, respectively,
compared to mean baseline testosterone concentrations.
A separate study was conducted
to evaluate the potential for testosterone transfer from 16 males dosed with
AndroGel 1.62% 81 mg when it was applied to abdomen only for 7 days, a site of application
not approved for AndroGel 1.62%. Two (2) hours after application to the males
on each day, the female subjects rubbed their abdomens for 15 minutes to the
abdomen of the males. The males had covered the application area with a
T-shirt. The mean testosterone Cavg and Cmax in female subjects on day 1
increased by 43% and 47%, respectively, compared to mean baseline testosterone
concentrations. The mean testosterone Cavg and Cmax in female subjects on day 7
increased by 60% and 58%, respectively, compared to mean baseline testosterone
concentrations.
Effect of Showering
In a randomized, 3-way (3
treatment periods without washout period) crossover study in 24 hypogonadal
men, the effect of showering on testosterone exposure was assessed after once
daily application of AndroGel 1.62% 81 mg to upper arms/shoulders for 7 days in
each treatment period. On the 7th day of each treatment period, hypogonadal men
took a shower with soap and water at either 2, 6, or 10 hours after drug
application. The effect of showering at 2 or 6 hours post-dose on Day 7 resulted
in 13% and 12% decreases in mean Cavg, respectively, compared to Day 6 when no
shower was taken after drug application. Showering at 10 hours after drug application
had no effect on bioavailability. The amount of testosterone remaining in the
outer layers of the skin at the application site on the 7th day was assessed
using a tape stripping procedure and was reduced by at least 80% after
showering 2-10 hours post-dose compared to on the 6th day when no shower was
taken after drug application.
Effect of Hand Washing
In a randomized, open-label,
single-dose, 2-way crossover study in 16 healthy male subjects, the effect of
hand washing on the amount of residual testosterone on the hands was evaluated.
Subjects used their hands to apply the maximum dose (81 mg testosterone) of
AndroGel 1.62% to their upper arms and shoulders. Within 1 minute of applying
the gel, subjects either washed or did not wash their hands prior to study
personnel wiping the subjects' hands with ethanol dampened gauze pads. The
gauze pads were then analyzed for residual testosterone content. A mean (SD) of
0.1 (0.04) mg of residual testosterone (0.12% of the actual applied dose of testosterone,
and a 96% reduction compared to when hands were not washed) was recovered after
washing hands with water and soap.
Effect of Sunscreen Or Moisturizing Lotion On Absorption Of Testosterone
In a randomized, 3-way (3
treatment periods without washout period) crossover study in 18 hypogonadal
males, the effect of applying a moisturizing lotion or a sunscreen on the
absorption of testosterone was evaluated with the upper arms/shoulders as
application sites. For 7 days, moisturizing lotion or sunscreen (SPF 50) was
applied daily to the AndroGel 1.62% application site 1 hour after the
application of AndroGel 1.62% 40.5 mg. Application of moisturizing lotion increased
mean testosterone Cavg and Cmax by 14% and 17%, respectively, compared to AndroGel
1.62% administered alone. Application of sunscreen increased mean testosterone
Cavg and Cmax by 8% and 13%, respectively, compared to AndroGel 1.62% applied
alone.
Clinical Studies
Clinical Trials In Hypogonadal
Males
AndroGel 1.62% was evaluated in
a multi-center, randomized, double-blind, parallel-group, placebo-controlled
study (182-day double-blind period) in 274 hypogonadal men with body mass index
(BMI) 18-40 kg/m² and 18-80 years of age (mean age 53.8 years). The patients
had an average serum testosterone concentration of < 300 ng/dL, as determined
by two morning samples collected on the same visit. Patients were Caucasian
83%, Black 13%, Asian or Native American 4%. 7.5% of patients were Hispanic.
Patients were randomized to
receive active treatment or placebo using a rotation method utilizing the
abdomen and upper arms/shoulders for 182 days. All patients were started at a
daily dose of 40.5 mg (two pump actuations) AndroGel 1.62% or matching placebo
on Day 1 of the study. Patients returned to the clinic on Day 14, Day 28, and
Day 42 for predose serum total testosterone assessments. The patient's daily
dose was titrated up or down in 20.25 mg increments if the predose serum
testosterone value was outside the range of 350-750 ng/dL. The study included
four active AndroGel 1.62% doses: 20.25 mg, 40.5 mg, 60.75 mg, and 81 mg daily.
The primary endpoint was the
percentage of patients with Cavg within the normal range of 300- 1000 ng/dL on
Day 112. In patients treated with AndroGel 1.62%, 81.6% (146/179) had Cavg within
the normal range at Day 112. 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 112 were 11.2% and 5.5%, respectively. Two patients had a Cmax > 2500
ng/dL on Day 112 (2510 ng/dL and 2550 ng/dL, respectively); neither of these 2
patients demonstrated an abnormal Cmax on prior or subsequent assessments at
the same dose.
Patients could agree to
continue in an open-label, active treatment maintenance period of the study for
an additional 182 days.
Dose titrations on Days 14, 28,
and 42 resulted in final doses of 20.25 mg – 81 mg on Day 112 as shown in Table
6.
Table 6: Mean (SD)
Testosterone Concentrations (Cavg and Cmax) by final dose on Days 112 and 364
Parameter |
Final Dose on Day 112 |
All Active
(n=179) |
Placebo
(n=27) |
20.25 mg
(n=12) |
40.5 mg
(n=34) |
60.75 mg
(n=54) |
81 mg
(n=79) |
Cavg (ng/dL) |
303 (135) |
457 (275) |
524(228) |
643 (285) |
537 (240) |
561 (259) |
Cmax (ng/dL) |
450 (349) |
663 (473) |
798 (439) |
958 (497) |
813 (479) |
845(480) |
|
Final Dose on Day 364 |
|
|
|
20.25 mg (n=7) |
40.5 mg (n=26) |
60.75 mg (n=29) |
81 mg (n=74) |
Continuing Active (n=136) |
Cavg (ng/dL) |
|
386 (130) |
474 (176) |
513 (222) |
432 (186) |
455 (192) |
Cmax (ng/dL) |
|
562(187) |
715 (306) |
839 (568) |
649 (329) |
697 (389) |
Figure 3 summarizes the
pharmacokinetic profile of total testosterone in patients completing 112 days
of AndroGel 1.62% treatment administered as a starting dose of 40.5 mg of
testosterone (2 pump actuations) for the initial 14 days followed by possible
titration according to the follow-up testosterone measurements.
Figure 3: Mean (±SD)
Steady-State Serum Total Testosterone Concentrations on Day 112
Efficacy was maintained in the
group of men that received AndroGel 1.62% for one full year. In that group, 78%
(106/136) had average serum testosterone concentrations in the normal range at Day
364. Figure 4 summarizes the mean total testosterone profile for these patients
on Day 364.
Figure 4: Mean (±SD)
Steady-State Serum Total Testosterone Concentrations on Day 364
The mean estradiol and DHT
concentration profiles paralleled the changes observed in testosterone. The
levels of LH and FSH decreased with testosterone treatment. The decreases in levels
of LH and FSH are consistent with reports published in the literature of
long-term treatment with testosterone.