CLINICAL PHARMACOLOGY
Mechanism Of Action
Leuprolide Acetate for Depot Suspension
Leuprolide acetate for depot suspension is a long-acting
GnRH analog. A single injection of leuprolide acetate for depot suspension
results in an initial elevation followed by a prolonged suppression of
pituitary gonadotropins. Repeated dosing at quarterly intervals results in decreased
secretion of gonadal steroids; consequently, tissues and functions that depend
on gonadal steroids for their maintenance become quiescent. This effect is
reversible on discontinuation of drug therapy.
Leuprolide acetate is not active when given orally.
Norethindrone Acetate
Norethindrone acetate induces secretory changes in an
estrogen-primed endometrium.
Pharmacodynamics
In a pharmacokinetic/pharmacodynamic study of leuprolide
acetate 11.25 mg for 3-month administration in healthy female subjects (N=20),
the onset of estradiol suppression was observed for individual subjects between
day 4 and week 4 after dosing. By the third week following the injection, the
mean estradiol concentration (8 pg/mL) was in the menopausal range. Throughout
the remainder of the dosing period, mean serum estradiol levels ranged from the
menopausal to the early follicular range.
Serum estradiol was suppressed to ≤ 20 pg/mL in all
subjects within four weeks and remained suppressed ( ≤ 40 pg/mL) in 80% of
subjects until the end of the 12-week dosing interval, at which time two of
these subjects had a value between 40 and 50 pg/mL. Four additional subjects had
at least two consecutive elevations of estradiol (range 43-240 pg/mL) levels
during the 12- week dosing interval, but there was no indication of luteal
function for any of the subjects during this period.
Pharmacokinetics
Absorption
Leuprolide Acetate for Depot Suspension
Following a single injection of the three month
formulation of leuprolide acetate for depot suspension (11.25 mg) in female
subjects, a mean plasma leuprolide concentration of 36.3 ng/mL was observed at
4 hours. Leuprolide appeared to be released at a constant rate following the onset
of steady-state levels during the third week after dosing and mean levels then
declined gradually to near the lower limit of detection by 12 weeks. The mean
(± standard deviation) leuprolide concentration from 3 to 12 weeks was 0.23 ±
0.09 ng/mL. However, intact leuprolide and an inactive major metabolite could
not be distinguished by the assay which was employed in the study. The initial
burst, followed by the rapid decline to a steady-state level, was similar to the
release pattern seen with the monthly formulation.
Norethindrone Acetate
Norethindrone acetate is deacetylated to norethindrone
after oral administration, and the disposition of norethindrone acetate is
indistinguishable from that of orally administered norethindrone. Norethindrone
acetate is absorbed from norethindrone acetate tablets, with maximum plasma
concentration of norethindrone generally occurring at about 2 hours post-dose (see
Figure 8). The pharmacokinetic parameters of norethindrone following single
oral administration of 5 mg norethindrone acetate under fasting conditions in
29 healthy female volunteers are summarized in Table 5.
Table 5: Pharmacokinetic Parameters after a Single
Dose of Norethindrone Acetate in Healthy Women
|
Norethindrone Acetate (n=29) Arithmetic Mean ± SD |
Norethindrone |
|
AUC (0-inf) (ng/ml*h) |
166.90 ± 56.28 |
Cmax (ng/ml) |
26.19 ± 6.19 |
tmax (h) |
1.83 ± 0.58 |
t½ (h) |
8.51 ± 2.19 |
AUC = area under the curve,
Cmax = maximum plasma concentration,
tmax = time at maximum plasma concentration,
t½ = half-life,
SD = standard deviation |
Figure 8: Mean Norethindrone Plasma Concentration
Profile after a Single Dose of 5 mg Norethindrone Acetate Administered to 29
Healthy Female Volunteers under Fasting Conditions
Effect of Food
The effect of food administration on the pharmacokinetics
of norethindrone acetate has not been studied.
Distribution
Leuprolide Acetate for Depot Suspension
The mean steady-state volume of distribution of
leuprolide following intravenous bolus administration to healthy male
volunteers was 27 L. In vitro binding to human plasma proteins ranged from 43%
to 49%.
Norethindrone Acetate
Norethindrone is 36% bound to sex hormone-binding
globulin (SHBG) and 61% bound to albumin. Volume of distribution of
norethindrone is about 4 L/kg.
Metabolism
Leuprolide Acetate for Depot Suspension
In healthy male volunteers, a 1 mg bolus of leuprolide
administered intravenously revealed that the mean systemic clearance was 7.6 L/h,
with a terminal elimination half-life of approximately 3 hours based on a two
compartment model.
In rats and dogs, administration of 14C-labeled
leuprolide was shown to be metabolized to smaller inactive peptides, a
pentapeptide (Metabolite I), tripeptides (Metabolites II and III) and a dipeptide
(Metabolite IV). These fragments may be further catabolized.
In a pharmacokinetic/pharmacodynamic study of
endometriosis patients, intramuscular 11.25 mg leuprolide acetate for depot
suspension (n=19) every 12 weeks or intramuscular 3.75 mg leuprolide acetate
for depot suspension (n=15) every 4 weeks was administered for 24 weeks. Â There
was no statistically significant difference in changes of serum estradiol
concentration from baseline between the 2 treatment groups.
M-I plasma concentrations measured in 5 prostate cancer
patients reached maximum concentration 2 to 6 hours after dosing and were
approximately 6% of the peak parent drug concentration. One week after dosing,
mean plasma M-I concentrations were approximately 20% of mean leuprolide
concentrations.
Norethindrone Acetate
Norethindrone undergoes extensive biotransformation,
primarily via reduction, followed by sulfate and glucuronide conjugation. The
majority of metabolites in the circulation are sulfates, with glucuronides
accounting for most of the urinary metabolites.
Excretion
Leuprolide Acetate for Depot Suspension
Following administration of leuprolide acetate for depot
suspension 3.75 mg for 1-month administration to 3 patients, less than 5% of
the dose was recovered as parent and M-I metabolite in the urine.
Norethindrone Acetate
Plasma clearance value for norethindrone is approximately
0.4 L/hr/kg. Norethindrone is excreted in both urine and feces, primarily as
metabolites. The mean terminal elimination halflife of norethindrone following
a single dose administration of norethindrone acetate is approximately 9 hours.
Specific Populations
Hepatic Impairment
The effect of hepatic disease on the disposition of
norethindrone after norethindrone acetate administration has not been
evaluated. However, norethindrone acetate is contraindicated in markedly
impaired liver function or liver disease [see CONTRAINDICATIONS].
The pharmacokinetics of the leuprolide acetate for depot
suspension in hepatically impaired patients has not been determined.
Renal Impairment
The effect of renal disease on the disposition of
norethindrone after norethindrone acetateadministration has not been evaluated.
In pre-menopausal women with chronic renal failure undergoing peritoneal dialysis who received multiple doses of an oral contraceptive containing ethinyl
estradiol and norethindrone, plasma norethindrone concentration was unchanged compared
to concentrations in pre-menopausal women with normal renal function.
The pharmacokinetics of the leuprolide acetate for depot
suspension in renally impaired patients has not been determined.
Race
The effect of race on the disposition of norethindrone
after norethindrone acetate administration has not been evaluated.
Drug Interactions
Leuprolide Acetate for Depot Suspension
Leuprolide acetate for depot suspension is a peptide that
is primarily degraded by peptidase and not by cytochrome P-450 enzymes as noted
in specific studies, and the drug is only about 46% bound to plasma proteins,
drug interactions would not be expected to occur.
Clinical Studies
Leuprolide Acetate For Depot Suspension
Initial endometriosis efficacy data for leuprolide
acetate for depot suspension were based on the 3.75 mg dose administered once
monthly.
A pharmacokinetic/pharmacodynamic study in 41 women that
included both the 3.75 mg dose administered once monthly and the 11.25 mg dose
administered once every three months did not reveal clinically significant
differences in terms of efficacy in reducing painful symptoms of endometriosis
or magnitude of the decrease in bone mineral density (BMD) associated with use of
leuprolide acetate.
Leuprolide Acetate For Depot Suspension Plus
Norethindrone Acetate
Two clinical studies with treatment duration of 12 months
were conducted to evaluate the effect of coadministration of leuprolide acetate
for depot suspension and norethindrone acetate on the loss of bone mineral
density (BMD) associated with leuprolide acetate for depot suspension and on
the efficacy of leuprolide acetate for depot suspension in relieving symptoms
of endometriosis. (All patients in these studies received calcium
supplementation with 1000 mg elemental calcium). A total of 242 women were
treated with monthly administration of leuprolide acetate 3.75 mg (13
injections) and with 5 mg norethindrone acetate taken daily. The population age
range was 17-43 years old. The majority of patients were Caucasian (87%).
One coadministration study was a controlled, randomized
and double-blind study included 51 women treated monthly with leuprolide
acetate for depot suspension alone and 55 women treated monthly with leuprolide
acetate for depot suspension plus norethindrone acetate daily. Women in this
trial were followed for up to 24 months after completing one year of treatment.
The other study was an open-label single arm clinical study in 136 women of one
year of treatment with leuprolide acetate for depot suspension and
norethindrone acetate, with follow-up for up to 12 months after completing
treatment.
The second study was an open label, single arm study in
which 136 women were treated monthly with leuprolide acetate for depot
suspension plus norethindrone acetate daily, with follow-up for up to 12 months
after completing treatment.
The assessment of efficacy was based on the
investigator's or the patient's monthly assessment of five signs or symptoms of
endometriosis (dysmenorrhea, pelvic pain, deep dyspareunia, pelvic tenderness
and pelvic induration).
Table 6 below provides detailed efficacy data regarding
relief of symptoms of endometriosis based on the two studies of
coadministration of leuprolide acetate and norethindrone acetate.
Table 6: Percentages of Patients with Symptoms of
Endometriosis and Mean Clinical Severity Scores
Variable |
Study |
Group |
Percent of Patients with Symptom |
Clinical Pain Severity Score |
Baseline |
Final |
Baseline |
Final |
N1 |
(%)2 |
(%) |
N1 |
Value3 |
Change |
Dysmenorrhea |
Controlled Study |
LA* |
51 |
(100) |
(4) |
50 |
3.2 |
-2.0 |
LA/N† |
55 |
(100) |
(4) |
54 |
3.1 |
-2.0 |
Open Label Study |
LA/N |
136 |
(99) |
(9) |
134 |
3.3 |
-2.1 |
Pelvic Pain |
Controlled Study |
LA |
51 |
(100) |
(66) |
50 |
2.9 |
-1.1 |
LA/N |
55 |
(96) |
(56) |
54 |
3.1 |
-1.1 |
Open Label Study |
LA/N |
136 |
(99) |
(63) |
134 |
3.2 |
-1.2 |
Deep Dyspareunia |
Controlled Study |
LA |
42 |
(83) |
(37) |
25 |
2.4 |
-1.0 |
LA/N |
43 |
(84) |
(45) |
30 |
2.7 |
-0.8 |
Open Label Study |
LA/N |
102 |
(91) |
(53) |
94 |
2.7 |
-1.0 |
Pelvic Tenderness |
Controlled Study |
LA |
51 |
(94) |
(34) |
50 |
2.5 |
-1.0 |
LA/N |
54 |
(91) |
(34) |
52 |
2.6 |
-0.9 |
Open Label Study |
LA/N |
136 |
(99) |
(39) |
134 |
2.9 |
-1.4 |
Pelvic Induration |
Controlled Study |
LA |
51 |
(51) |
(12) |
50 |
1.9 |
-0.4 |
LA/N |
54 |
(46) |
(17) |
52 |
1.6 |
-0.4 |
Open Label Study |
LA/N |
136 |
(75) |
(21) |
134 |
2.2 |
-0.9 |
* LA = leuprolide acetate 3.75 mg
† LA/N = leuprolide acetate 3.75 mg plus norethindrone acetate 5 mg
1 Number of patients that were included in the assessment
2 Percentage of patients with the symptom/sign
3 Value description: 1=none; 2= mild; 3= moderate; 4= severe |
Suppression of menses (menses was defined as three or
more consecutive days of menstrual bleeding) was maintained throughout
treatment in 84% and 73% of patients receiving leuprolide acetate and
norethindrone acetate, in the controlled study and open label study,
respectively. The median time for menses resumption after treatment with
leuprolide acetate and norethindrone acetate was 8 weeks.
Changes in Bone Density
The effect of leuprolide acetate for depot suspension and
norethindrone acetate on bone mineral density was evaluated by dual energy
x-ray absorptiometry (DXA) scan in the two clinical trials. For the open-label
study, success in mitigating BMD loss was defined as the lower bound of the 95%
confidence interval around the change from baseline at one year of treatment
not to exceed –2.2%. The bone mineral density data of the lumbar spine from
these two studies are presented in Table 7.
Table 7: Mean Percent Change from Baseline in BMD of
Lumbar Spine
|
leuprolide acetate for depot suspension 3.75 mg |
leuprolide acetate for depot suspension 3.75 mg plus norethindrone acetate 5 mg daily |
Controlled Study |
Controlled Study |
Open Label Study |
N |
Change (Mean, 95% CI)# |
N |
Change (Mean, 95% CI)# |
N |
Change (Mean, 95% CI)# |
Week 24* |
41 |
-3.2% (-3.8, -2.6) |
42 |
-0.3% (-0.8, 0.3) |
115 |
-0.2% (-0.6, 0.2) |
Week 52† |
29 |
-6.3% (-7.1, -5.4) |
32 |
-1.0% (-1.9, -0.1) |
84 |
-1.1% (-1.6, -0.5) |
* Includes on-treatment measurements that fell within
2-252 days after the first day of treatment.
† Includes on-treatment measurements > 252 days after the first day of
treatment.
# 95% CI: 95% Confidence Interval |
The change in BMD following discontinuation of treatment
is shown in Table 8.
Table 8: Mean Percent Change from Baseline in BMD of
Lumbar Spine in Post-Treatment Follow-up Period
Post Treatment Measurement |
Controlled Study |
Open Label Study |
LA-Only |
LA/N |
LA/N |
N |
Mean % Change |
95% CI (%) |
N |
Mean % Change |
95% CI (%) |
N |
Mean % Change |
95% CI (%)2 |
Month 8 |
19 |
-3.3 |
(-4.9, -18) |
23 |
-0.9 |
(-2.1, 0.4) |
89 |
-0.6 |
(-1.2, 0.0) |
Month 12 |
16 |
-2.2 |
(-3.3, -11) |
12 |
-0.7 |
(-2.1, 0.6) |
65 |
0.1 |
(-0.6, 0.7) |
1 Patients with post treatment measurements
2 95% CI (2-sided) of percent change in BMD values from baseline |
These clinical studies demonstrated that coadministration
of leuprolide acetate and norethindrone acetate 5 mg daily is effective in
significantly reducing the loss of bone mineral density that occurs with
leuprolide acetate for depot suspension treatment, and in relieving symptoms of
endometriosis.