CLINICAL PHARMACOLOGY
Actonel
Mechanism of Action
Actonel has an affinity for hydroxyapatite crystals in bone and acts as an
antiresorptive agent. At the cellular level, Actonel inhibits osteoclasts. The
osteoclasts adhere normally to the bone surface, but show evidence of reduced
active resorption (e.g., lack of ruffled border). Histomorphometry in rats,
dogs, and minipigs showed that Actonel treatment reduces bone turnover (activation
frequency, i.e., the rate at which bone remodeling sites are activated) and
bone resorption at remodeling sites.
Pharmacokinetics
Absorption
Absorption after an oral dose is relatively rapid (tmax ~1 hour) and occurs
throughout the upper gastrointestinal tract. The fraction of the dose absorbed
is independent of dose over the range studied (single dose, 2.5 to 30 mg; multiple
dose, 2.5 to 5 mg). Steady-state conditions in the serum are observed within
57 days of daily dosing. Mean absolute oral bioavailability of the 30 mg tablet
is 0.63% (90% CI: 0.54% to 0.75%) and is comparable to a solution. The extent
of absorption of a 30 mg dose (three 10 mg tablets) when administered 0.5 hours
before breakfast is reduced by 55% compared to dosing in the fasting state (no
food or drink for 10 hours prior to or 4 hours after dosing). Dosing 1 hour
prior to breakfast reduces the extent of absorption by 30% compared to dosing
in the fasting state. Dosing either 0.5 hours prior to breakfast or 2 hours
after dinner (evening meal) results in a similar extent of absorption. Actonel
is effective when administered at least 30 minutes before breakfast.
Distribution
The mean steady-state volume of distribution is 6.3 L/kg in humans. Human plasma protein binding of drug is about 24%. Preclinical studies in rats and dogs dosed
intravenously with single doses of [14C] risedronate indicate that
approximately 60% of the dose is distributed to bone. The remainder of the dose
is excreted in the urine. After multiple oral dosing in rats, the uptake of
risedronate in soft tissues was in the range of 0.001% to 0.01%.
Metabolism
There is no evidence of systemic metabolism of risedronate.
Elimination
Approximately half of the absorbed dose is excreted in urine within 24 hours,
and 85% of an intravenous dose is recovered in the urine over 28 days. Mean
renal clearance is 105 mL/min (CV = 34%) and mean total clearance is 122 mL/min
(CV = 19%), with the difference primarily reflecting nonrenal clearance or clearance
due to adsorption to bone. The renal clearance is not concentration dependent,
and there is a linear relationship between renal clearance and creatinine clearance.
Unabsorbed drug is eliminated unchanged in feces. Once risedronate is absorbed,
the serum concentration-time profile is multi-phasic, with an initial half-life
of about 1.5 hours and a terminal exponential half-life of 480 hours. This terminal
half-life is hypothesized to represent the dissociation of risedronate from
the surface of bone.
Calcium
Calcium is a major substrate for mineralization and has an antiresorptive effect
on bone. Calcium suppresses PTH secretion and decreases bone turnover. Increased
levels of PTH are known to contribute to age-related bone loss, especially at
cortical sites, while increased bone turnover is an independent risk factor
of fractures.
Pharmacokinetics
Absorption
Calcium is released from calcium complexes during digestion in a soluble, ionized
form, for absorption from the small intestine. Absorption can be by both passive
and active mechanisms. Active absorption of calcium is highly dependent on vitamin
D, and vitamin D deficiency decreases the absorption of calcium. As calcium
intake increases, the active transfer mechanism becomes saturated and an increasing
proportion of calcium is absorbed via passive diffusion. Absorption of calcium
carbonate is dose-dependent, with fractional absorption being highest when at
doses up to 500 mg. Absorption of calcium is also dependent on pH with reduced
absorption in alkaline conditions. The absorption of calcium from calcium carbonate
is increased when taken with food.
Distribution
Approximately 50% of calcium in the serum is in the physiologically active
ionized form; about 10% is complexed to phosphate, citrate or other anions.
The remaining 40% is bound to proteins, primarily albumin.
Elimination
Unabsorbed calcium from the small intestine is excreted in the feces. Renal
excretion depends largely on glomerular filtration and calcium tubular reabsorption
with more than 98% of calcium reabsorbed from the glomerular filtrate. This
process is regulated by active vitamin D and PTH.
Special Populations
Actonel
Pediatric
Risedronate pharmacokinetics have not been studied in patients < 18 years
of age.
Gender
Bioavailability and pharmacokinetics following oral administration are similar
in men and women.
Geriatric
Bioavailability and disposition are similar in elderly ( > 60 years of age)
and younger subjects. No dosage adjustment is necessary.
Race
Pharmacokinetic differences due to race have not been studied.
Renal Insufficiency
Risedronate is excreted unchanged primarily via the kidney. As compared to
persons with normal renal function, the renal clearance of risedronate was decreased
by about 70% in patients with creatinine clearance of approximately 30 mL/min.
Actonel is not recommended for use in patients with severe renal impairment
(creatinine clearance < 30 mL/min) because of lack of clinical experience.
No dosage adjustment is necessary in patients with a creatinine clearance ≥ 30
mL/min.
Hepatic Insufficiency
No studies have been performed to assess risedronate's safety or efficacy in
patients with hepatic impairment. Risedronate is not metabolized in rat, dog,
and human liver preparations. Insignificant amounts ( < 0.1% of intravenous
dose) of drug are excreted in the bile in rats. Therefore, dosage adjustment
is unlikely to be needed in patients with hepatic impairment.
Calcium
Absorption of calcium from calcium carbonate is poor in patients with achlorhydria
unless taken with food.
Gender
Absorption of calcium from calcium carbonate has not been adequately studied
with respect to gender.
Geriatric
There are no clinically significant differences in bioavailability following
administration of 1 g elemental calcium as calcium carbonate between young (20
to 27 years) and elderly (63 to 71 years) females.
Race
The effect of race on calcium absorption from oral calcium carbonate has not
been studied.
Renal Insufficiency
Renal disease affects calcium homeostasis through its effects on vitamin D
metabolism, phosphorus excretion, and PTH. Calcium should be administered cautiously
to patients with renal disease (creatinine clearance < 30 mL/min) to avoid
elevations of the calcium-phosphorus ion product (Ca x Phos) and the development
of calcinosis.
Pharmacodynamics
Actonel
Treatment and Prevention of Osteoporokis in Postmenopausal Women
Osteoporosis is characterized by decreased bone mass and increased fracture
risk, most commonly at the spine, hip, and wrist.
The diagnosis can be confirmed by the finding of low bone mass, evidence of
fracture on x-ray, a history of osteoporotic fracture, or height loss or kyphosis indicative of vertebral fracture.
Osteoporosis occurs in both men and women but is more common among women following
menopause. In healthy humans, bone formation and resorption are closely linked;
old bone is resorbed and replaced by newly-formed bone. In postmenopausal osteoporosis,
bone resorption exceeds bone formation, leading to bone loss and increased risk
of bone fracture. After menopause, the risk of fractures of the spine and hip
increases; approximately 40% of 50 year-old women will experience an osteoporosis-related
fracture during their remaining lifetimes. After experiencing 1 osteoporosis-related
fracture, the risk of future fracture increases 5-fold compared to the risk
among a non-fractured population.
Actonel treatment decreases the elevated rate of bone turnover that is typically
seen in postmenopausal osteoporosis. In clinical trials, administration of Actonel
to postmenopausal women resulted in decreases in biochemical markers of bone
turnover, including urinary deoxypyridinoline/creatinine and urinary collagen
cross-linked N-telopeptide (markers of bone resorption) and serum bone specific
alkaline phosphatase (a marker of bone formation). At the 5 mg dose, decreases
in deoxypyridinoline/creatinine were evident within 14 days of treatment. Changes
in bone formation markers were observed later than changes in resorption markers,
as expected, due to the coupled nature of bone resorption and bone formation;
decreases in bone specific alkaline phosphatase of about 20% were evident within
3 months of treatment. Bone turnover markers reached a nadir of about 40% below
baseline values by the sixth month of treatment and remained stable with continued
treatment for up to 3 years. Bone turnover is decreased as early as 14 days
and maximally within about 6 months of treatment, with achievement of a new
steady-state that more nearly approximates the rate of bone turnover seen in
premenopausal women. In a 1-year study comparing daily versus weekly oral dosing
regimens of Actonel for the treatment of osteoporosis in postmenopausal women,
Actonel 5 mg daily and Actonel 35 mg once-a-week decreased urinary collagen
cross-linked N-telopeptide by 60% and 61%, respectively. In addition, serum
bone-specific alkaline phosphatase was also reduced by 42% and 41% in the Actonel
5 mg daily and Actonel 35 mg once-a-week groups, respectively. Actonel is not
an estrogen and does not have the benefits and risks of estrogen therapy.
As a result of the inhibition of bone resorption, asymptomatic and usually
transient decreases from baseline in serum calcium ( < 1%) and serum phosphate
( < 3%) and compensatory increases in serum PTH levels ( < 30%) were observed
within 6 months in patients in osteoporosis clinical trials. There were no significant
differences in serum calcium, phosphate, or PTH levels between the Actonel and
placebo groups at 3 years. In a 1-year study comparing daily versus weekly oral
dosing regimens of Actonel in postmenopausal women, the mean changes from baseline
at 12 months were similar between the Actonel 5 mg daily and Actonel 35 mg once-a-week
groups, respectively, for serum calcium (0.4% and 0.7%), phosphate (-3.8% and
-2.6%) and PTH (6.4% and 4.2%).
Calcium
Calcium administration decreases the elevated rate of bone turnover typically
seen in postmenopausal women with osteoporosis. In randomized, placebo controlled
studies in postmenopausal women, calcium administration (500 mg to 1600 mg)
decreased biochemical markers of bone turnover, including urine N-telopeptide,
urine free pyridinoline (markers of bone resorption), alkaline phosphatase and
osteocalcin (markers of bone formation) relative to placebo treated women.
Calcium administration may transiently increase levels of serum calcium with
compensatory reductions in serum PTH and an increase in urinary calcium. However,
urinary and serum calcium levels usually remain within the normal reference
range.
Clinical Studies
Actonel
Treatment of Osteoporosis in Postmenopausal Women
The fracture efficacy of Actonel 5 mg daily in the treatment of postmenopausal
osteoporosis was demonstrated in 2 large, randomized, placebo-controlled, double-blind
studies that enrolled a total of almost 4000 postmenopausal women under similar
protocols. The Multinational study (VERT MN) (Actonel 5 mg, n = 408) was conducted
primarily in Europe and Australia; a second study was conducted in North America
(VERT NA) (Actonel 5 mg, n = 821). Patients were selected on the basis of radiographic
evidence of previous vertebral fracture, and therefore, had established disease.
The average number of prevalent vertebral fractures per patient at study entry
was 4 in VERT MN, and 2.5 in VERT NA, with a broad range of baseline bone mineral
density (BMD) levels. All patients in these studies received supplemental calcium
1000 mg/day. Patients with low vitamin D levels (approximately 40 nmol/L or
less) also received supplemental vitamin D 500 IU/day.
Positive effects of Actonel treatment on BMD were also demonstrated in each
of 2 large, randomized, placebo-controlled trials (BMD MN and BMD NA) in which
almost 1200 postmenopausal women (Actonel 5 mg, n = 394) were recruited on the
basis of low lumbar spine bone mass (more than 2 SD below the premenopausal
mean) rather than a history of vertebral fracture.
Actonel 35 mg once-a-week (n = 485) was shown to be therapeutically equivalent
to Actonel 5 mg daily (n = 480) in a 1-year, double-blind, multicenter study
of postmenopausal women with osteoporosis. In the primary efficacy analkysis
of completers, the mean increases from baseline in lumbar spine BMD at 1 year
were 4.0% (3.7, 4.3; 95% confidence interval [CI]) in the 5 mg daily group (n
= 391) and 3.9% (3.6, 4.3; 95% CI) in the 35 mg once-a-week group (n = 387)
and the mean difference between 5 mg daily and 35 mg weekly was 0.1% (-0.42,
0.55; 95% CI). The results of the intent-to-treat analysis with the last observation
carried forward were consistent with the primary efficacy analysis of completers.
The 2 treatment groups were also similar with regard to BMD increases at other
skeletal sites.
Effect on Vertebral Fractures
Fractures of previously undeformed vertebrae (new fractures) and worsening
of pre-existing vertebral fractures were diagnosed radiographically; some of
these fractures were also associated with symptoms (i.e., clinical fractures).
Spinal radiographs were scheduled annually and prospectively planned analyses
were based on the time to a patient's first diagnosed fracture. The primary
endpoint for these studies was the incidence of new and worsening vertebral
fractures across the period of 0 to 3 years. Actonel 5 mg daily significantly
reduced the incidence of new and worsening vertebral fractures and of new vertebral
fractures in both VERT NA and VERT MN at all time points (Table 1). The reduction
in risk seen in the subgroup of patients who had 2 or more vertebral fractures
at study entry was similar to that seen in the overall study population.
Table 1 : The Effect of Actonel on the Risk of Vertebral
Fractures
VERT NA |
Proportion of Patients |
Absolute Risk Reduction (%) |
Relative Risk Reduction (%) |
with Fracture (%)a |
Placebo
n = 678 |
Actonel 5 mg
n = 696 |
New and Worsening |
0 to 1 Year |
7.2 |
3.9 |
3.3 |
49 |
0 to 2 Years |
12.8 |
8.0 |
4.8 |
42 |
0 to 3 Years |
18.5 |
13.9 |
4.6 |
33 |
New |
0 to 1 Year |
6.4 |
2.4 |
4.0 |
65 |
0 to 2 Years |
11.7 |
5.8 |
5.9 |
55 |
0 to 3 Years |
16.3 |
11.3 |
5.0 |
41 |
VERT MN |
Placebo
n = 346 |
Actonel 5 mg
n = 344 |
Absolute Risk Reduction (%) |
Relative Risk Reduction (%) |
New and Worsening |
0 to 1 Year |
15.3 |
8.2 |
7.1 |
50 |
0 to 2 Years |
28.3 |
13.9 |
14.4 |
56 |
0 to 3 Years |
34.0 |
21.8 |
12.2 |
46 |
New |
0 to 1 Year |
13.3 |
5.6 |
7.7 |
61 |
0 to 2 Years |
24.7 |
11.6 |
13.1 |
59 |
0 to 3 Years |
29.0 |
18.1 |
10.9 |
49 |
a Calculated by Kaplan-Meier methodology |
Effect on Osteoporosis-Related Nonvertebral Fractures
In VERT MN and VERT NA, a prospectively planned efficacy endpoint was defined
consisting of all radiographically confirmed fractures of skeletal sites accepted
as associated with osteoporosis. Fractures at these sites were collectively
referred to as osteoporosis-related nonvertebral fractures. Actonel 5 mg daily
significantly reduced the incidence of nonvertebral osteoporosis-related fractures
over 3 years in VERT NA (8% versus 5%; relative risk reduction 39%) and reduced
the fracture incidence in VERT MN from 16% to 11%. There was a significant reduction
from 11% to 7% when the studies were combined, with a corresponding 36% reduction
in relative risk. Figure 1 shows the overall results as well as the results
at the individual skeletal sites for the combined studies.
Figure 1: Nonvertebral Osteoporosis-Related Fractures
Cumulative
Incidence Over 3 Years
Combined VERT MN and VERT NA
Effect on Height
In the two 3-year osteoporosis treatment studies, standing height was measured
yearly by stadiometer. Both Actonel and placebo-treated groups lost height during
the studies. Patients who received Actonel had a statistically significantly
smaller loss of height than those who received placebo. In VERT MN, the median
annual height change was -1.3 mm/yr in the Actonel 5 mg daily group compared
to -2.4 mm/yr in the placebo group. In VERT NA, the median annual height change
was -0.7 mm/yr in the Actonel 5 mg daily group compared to -1.1 mm/yr in the
placebo group.
Effect on Bone Mineral Density
The results of 4 randomized, placebo-controlled trials in women with postmenopausal
osteoporosis (VERT MN, VERT NA, BMD MN, BMD NA) demonstrate that Actonel 5 mg
daily increases BMD at the spine, hip, and wrist compared to the effects seen
with placebo. Table 2 displays the significant increases in BMD seen at the
lumbar spine, femoral neck, femoral trochanter, and midshaft radius in these
trials compared to placebo. In both VERT studies (VERT MN and VERT NA), Actonel
5 mg daily produced increases in lumbar spine BMD that were progressive over
the 3 years of treatment, and were statistically significant relative to baseline
and to placebo at 6 months and at all later time points.
Table 2 : Mean Percent Increase in BMD from Baseline in Patients
Taking Actonel 5 mg or Placebo at Endpointa
|
VERT MNb |
VERT NAb |
BMD MNc |
BMD NAc |
Placebo
n = 323 |
5 mg
n = 323 |
Placebo
n = 599 |
5 mg
n = 606 |
Placebo
n = 161 |
5 mg
n = 148 |
Placebo
n = 191 |
5 mg
n = 193 |
Lumbar Spine |
1.0 |
6.6 |
0.8 |
5.0 |
0.0 |
4.0 |
0.2 |
4.8 |
Femoral Neck |
-1.4 |
1.6 |
-1.0 |
1.4 |
-1.1 |
1.3 |
0.1 |
2.4 |
Femoral Trochanter |
-1.9 |
3.9 |
-0.5 |
3.0 |
-0.6 |
2.5 |
1.3 |
4.0 |
Midshaft Radius |
-1.5* |
0.2* |
-1.2* |
0.1* |
ND |
ND |
a The endpoint value is the value
at the study's last time point for all patients who had BMD measured at
that time; otherwise the last postbaseline BMD value prior to the study's
last time point is used.
b The duration of the studies was 3 years.
c The duration of the studies was 1.5 to 2 years.
*BMD of the midshaft radius was measured in a subset of centers in VERT
MN (placebo, n = 222; 5 mg, n = 214) and VERT NA (placebo, n = 310; 5
mg, n = 306)
ND = analysis not done |
Histology/Histomorphometry
Bone biopsies from 110 postmenopausal women were obtained at endpoint. Patients
had received daily Actonel (2.5 mg or 5 mg) or placebo for 2 to 3 years. Histologic
evaluation (n = 103) showed no osteomalacia, impaired bone mineralization, or
other adverse effects on bone in Actonel-treated women. These findings demonstrate
that bone formed during Actonel administration is of normal quality. The histomorphometric
parameter mineralizing surface, an index of bone turnover, was assessed based
upon baseline and post-treatment biopsy samples from 23 patients treated with
Actonel 5 mg and 21 treated with placebo. Mineralizing surface decreased moderately
in Actonel-treated patients (median percent change: Actonel 5 mg, -74%; placebo,
-21%), consistent with the known effects of treatment on bone turnover.
Prevention of Osteoporosis in Postmenopausal Women
Actonel 5 mg daily prevented bone loss in a majority of postmenopausal women
(age range 42 to 63 years) within 3 years of menopause in a 2-year, double-blind,
placebo-controlled study in 383 patients (Actonel 5 mg, n = 129). All patients
in this study received supplemental calcium 1000 mg/day. Increases in BMD were
observed as early as 3 months following initiation of Actonel treatment. Actonel
5 mg produced significant mean increases in BMD at the lumbar spine, femoral
neck, and trochanter compared to placebo at the end of the study (Figure 2).
Actonel 5 mg daily was also effective in patients with lower baseline lumbar
spine BMD (more than 1 SD below the premenopausal mean) and in those with normal
baseline lumbar spine BMD. Bone mineral density at the distal radius decreased
in both Actonel and placebo-treated women following 1 year of treatment.
Figure 2 :Change in BMD from Baseline2-Year Prevention Study
 |
Actonel 35 mg once-a-week prevented bone loss in postmenopausal women (age
range 44 to 64 years) without osteoporosis in a 1-year, double-blind, placebo-controlled
study in 278 patients (Actonel 35 mg, n = 136). All patients were supplemented
with 1000 mg elemental calcium and 400 IU vitamin D per day. The primary efficacy
measure was the percent change in lumbar spine BMD from baseline after 1 year
of treatment using LOCF (last observation carried forward). Actonel 35 mg once-a-week
resulted in a statistically significant mean difference from placebo in lumbar
spine BMD of +2.9% (least square mean for risedronate +1.83%; placebo -1.05%).
Actonel 35 mg once-a-week also showed a statistically significant mean difference
from placebo in BMD at the total proximal femur of +1.5% (risedronate +1.01%;
placebo -0.53%), femoral neck of +1.2% (risedronate +0.22%; placebo -1.00%),
and trochanter of +1.8% (risedronate +1.07%; placebo -0.74%).
Combined Administration with Hormone Replacement Therapy
The effects of combining Actonel 5 mg daily with conjugated estrogen 0.625
mg daily (n = 263) were compared to the effects of conjugated estrogen alone
(n = 261) in a 1-year, randomized, double-blind study of women ages 37 to 82
years, who were on average 14 years postmenopausal. The BMD results for this
study are presented in Table 3.
Table 3 : Percent Change from Baseline in BMD After 1 Year
of Treatment
|
Estrogen 0.625 mg
n = 261 |
ACTONEL 5 mg ± Estrogen 0.625 mg
n = 263 |
Lumbar Spine |
4.6 ± 0.20 |
5.2 ± 0.23 |
Femoral Neck |
1.8 ± 0.25 |
2.7 ± 0.25 |
Femoral Trochanter |
3.2 ± 0.28 |
3.7 ± 0.25 |
Midshaft Radius |
0.4 ± 0.14 |
0.7 ± 0.17 |
Distal Radius |
1.7 ± 0.24 |
1.6 ± 0.28 |
Values shown are mean (± SEM) percent
change from baseline. |
Histology/Histomorphometry
Bone biopsies from 53 postmenopausal women were obtained at endpoint. Patients
had received Actonel 5 mg plus estrogen or estrogen alone once daily for 1 year.
Histologic evaluation (n = 47) demonstrated that the bone of patients treated
with Actonel plus estrogen was of normal lamellar structure and normal mineralization.
The histomorphometric parameter mineralizing surface, a measure of bone turnover,
was assessed based upon baseline and post-treatment biopsy samples from 12 patients
treated with Actonel plus estrogen and 12 treated with estrogen alone. Mineralizing
surface decreased in both treatment groups (median percent change: Actonel plus
estrogen, -79%; estrogen alone, -50%), consistent with the known effects of
these agents on bone turnover.
Animal Pharmacology And/Or Toxicology
Actonel
Risedronate demonstrated potent anti-osteoclast, antiresorptive activity in
ovariectomized rats and minipigs. Bone mass and biomechanical strength were
increased dose-dependently at oral doses up to 4 and 25 times the human recommended
oral dose of 35 mg/week based on surface area, (mg/m²) for rats and minipigs,
respectively. Risedronate treatment maintained the positive correlation between
BMD and bone strength and did not have a negative effect on bone structure or
mineralization. In intact dogs, risedronate induced positive bone balance at
the level of the bone remodeling unit at oral doses ranging from 0.35 to 1.4
times the human 35 mg/week dose based on surface area (mg/m²).
In dogs treated with an oral dose of 1 mg/kg/day (approximately 5 times the
human 35 mg/week dose based on surface area, mg/m²), risedronate caused
a delay in fracture healing of the radius. The observed delay in fracture healing
is similar to other bisphosphonates. This effect did not occur at a dose of
0.1 mg/kg/day (approximately 0.5 times the human 35 mg/week dose based on surface
area, mg/m²).
The Schenk rat assay, based on histologic examination of the epiphyses of growing
rats after drug treatment, demonstrated that risedronate did not interfere with
bone mineralization even at the highest dose tested (5 mg/kg/day, subcutaneously),
which was approximately 3500 times the lowest antiresorptive dose (1.5 mcg/kg/day
in this model) and approximately 8 times the human 35 mg/week dose based on
surface area (mg/m²). This indicates that Actonel administered at the therapeutic
dose is unlikely to induce osteomalacia.
Calcium
Published studies have demonstrated that changes in the dietary intake of calcium
affect bone growth and skeletal development in animals, as well as bone loss
in animal models of estrogendepletion/ovariectomy and aging.