CLINICAL PHARMACOLOGY
Mechanism Of Action
Endogenous 84-amino acid parathyroid hormone (PTH) is the
primary regulator of calcium and phosphate metabolism in bone and kidney.
Physiological actions of PTH include regulation of bone metabolism, renal
tubular reabsorption of calcium and phosphate, and intestinal calcium
absorption. The biological actions of PTH and teriparatide are mediated through
binding to specific high-affinity cellsurface receptors. Teriparatide and the
34 N-terminal amino acids of PTH bind to these receptors with the same affinity
and have the same physiological actions on bone and kidney. Teriparatide is not
expected to accumulate in bone or other tissues.
The skeletal effects of teriparatide depend upon the
pattern of systemic exposure. Once-daily administration of teriparatide
stimulates new bone formation on trabecular and cortical (periosteal and/or endosteal)
bone surfaces by preferential stimulation of osteoblastic activity over
osteoclastic activity. In monkey studies, teriparatide improved trabecular
microarchitecture and increased bone mass and strength by stimulating new bone
formation in both cancellous and cortical bone. In humans, the anabolic effects
of teriparatide manifest as an increase in skeletal mass, an increase in
markers of bone formation and resorption, and an increase in bone strength. By
contrast, continuous excess of endogenous PTH, as occurs in
hyperparathyroidism, may be detrimental to the skeleton because bone resorption
may be stimulated more than bone formation.
Pharmacodynamics
Pharmacodynamics In Men and Postmenopausal Women With Osteoporosis
Effects on Mineral Metabolism - Teriparatide
affects calcium and phosphorus metabolism in a pattern consistent with the
known actions of endogenous PTH (e.g., increases serum calcium and decreases serum
phosphorus).
Serum Calcium Concentrations - When teriparatide
20 mcg is administered once daily, the serum calcium concentration increases
transiently, beginning approximately 2 hours after dosing and reaching a
maximum concentration between 4 and 6 hours (median increase, 0.4 mg/dL). The
serum calcium concentration begins to decline approximately 6 hours after
dosing and returns to baseline by 16 to 24 hours after each dose.
In a clinical study of postmenopausal women with
osteoporosis, the median peak serum calcium concentration measured 4 to 6 hours
after dosing with FORTEO (teriparatide 20 mcg) was 2.42 mmol/L (9.68 mg/dL) at
12 months. The peak serum calcium remained below 2.76 mmol/L (11.0 mg/dL) in
> 99% of women at each visit. Sustained hypercalcemia was not observed.
In this study, 11.1% of women treated with FORTEO had at
least 1 serum calcium value above the upper limit of normal [2.64 mmol/L (10.6
mg/dL)] compared with 1.5% of women treated with placebo. The percentage of
women treated with FORTEO whose serum calcium was above the upper limit of
normal on consecutive 4- to 6-hour post-dose measurements was 3.0% compared
with 0.2% of women treated with placebo. In these women, calcium supplements
and/or FORTEO doses were reduced. The timing of these dose reductions was at
the discretion of the investigator. FORTEO dose adjustments were made at
varying intervals after the first observation of increased serum calcium
(median 21 weeks). During these intervals, there was no evidence of progressive
increases in serum calcium.
In a clinical study of men with either primary or
hypogonadal osteoporosis, the effects on serum calcium were similar to those
observed in postmenopausal women. The median peak serum calcium concentration
measured 4 to 6 hours after dosing with FORTEO was 2.35 mmol/L (9.44 mg/dL) at 12
months. The peak serum calcium remained below 2.76 mmol/L (11.0 mg/dL) in 98%
of men at each visit. Sustained hypercalcemia was not observed.
In this study, 6.0% of men treated with FORTEO daily had
at least 1 serum calcium value above the upper limit of normal [2.64 mmol/L
(10.6 mg/dL)] compared with none of the men treated with placebo. The
percentage of men treated with FORTEO whose serum calcium was above the upper
limit of normal on consecutive measurements was 1.3% (2 men) compared with none
of the men treated with placebo. Although calcium supplements and/or FORTEO
doses could have been reduced in these men, only calcium supplementation was
reduced [see WARNINGS AND PRECAUTIONS and ADVERSE REACTIONS].
In a clinical study of women previously treated for 18 to
39 months with raloxifene (n=26) or alendronate (n=33), mean serum calcium
> 12 hours after FORTEO injection was increased by 0.09 to 0.14 mmol/L (0.36
to 0.56 mg/dL), after 1 to 6 months of FORTEO treatment compared with baseline.
Of the women pretreated with raloxifene, 3 (11.5%) had a serum calcium > 2.76
mmol/L (11.0 mg/dL), and of those pretreated with alendronate, 3 (9.1%) had a
serum calcium > 2.76 mmol/L (11.0 mg/dL). The highest serum calcium reported
was 3.12 mmol/L (12.5 mg/dL). None of the women had symptoms of hypercalcemia.
There were no placebo controls in this study.
In the study of patients with glucocorticoid-induced
osteoporosis, the effects of FORTEO on serum calcium were similar to those
observed in postmenopausal women with osteoporosis not taking glucocorticoids.
Urinary Calcium Excretion - In a clinical study of
postmenopausal women with osteoporosis who received 1000 mg of supplemental
calcium and at least 400 IU of vitamin D, daily FORTEO increased urinary
calcium excretion. The median urinary excretion of calcium was 4.8 mmol/day
(190 mg/day) at 6 months and 4.2 mmol/day (170 mg/day) at 12 months. These
levels were 0.76 mmol/day (30 mg/day) and 0.3 mmol/day (12 mg/day) higher,
respectively, than in women treated with placebo. The incidence of
hypercalciuria ( > 7.5 mmol Ca/day or 300 mg/day) was similar in the women
treated with FORTEO or placebo.
In a clinical study of men with either primary or
hypogonadal osteoporosis who received 1000 mg of supplemental calcium and at
least 400 IU of vitamin D, daily FORTEO had inconsistent effects on urinary
calcium excretion. The median urinary excretion of calcium was 5.6 mmol/day
(220 mg/day) at 1 month and 5.3 mmol/day (210 mg/day) at 6 months. These levels
were 0.5 mmol/day (20 mg/day) higher and 0.2 mmol/day (8.0 mg/day) lower,
respectively, than in men treated with placebo. The incidence of hypercalciuria
( > 7.5 mmol Ca/day or 300 mg/day) was similar in the men treated with FORTEO
or placebo.
Phosphorus and Vitamin D - In single-dose studies,
teriparatide produced transient phosphaturia and mild transient reductions in
serum phosphorus concentration. However, hypophosphatemia ( < 0.74 mmol/L or
2.4 mg/dL) was not observed in clinical trials with FORTEO.
In clinical trials of daily FORTEO, the median serum
concentration of 1,25-dihydroxyvitamin D was increased at 12 months by 19% in
women and 14% in men, compared with baseline. In the placebo group, this
concentration decreased by 2% in women and increased by 5% in men. The median
serum 25- hydroxyvitamin D concentration at 12 months was decreased by 19% in
women and 10% in men compared with baseline. In the placebo group, this
concentration was unchanged in women and increased by 1% in men.
In the study of patients with glucocorticoid-induced
osteoporosis, the effects of FORTEO on serum phosphorus were similar to those
observed in postmenopausal women with osteoporosis not taking glucocorticoids.
Effects on Markers of Bone Turnover - Daily
administration of FORTEO to men and postmenopausal women with osteoporosis in
clinical studies stimulated bone formation, as shown by increases in the formation
markers serum bone-specific alkaline phosphatase (BSAP) and procollagen I
carboxyterminal propeptide (PICP). Data on biochemical markers of bone turnover
were available for the first 12 months of treatment. Peak concentrations of
PICP at 1 month of treatment were approximately 41% above baseline, followed by
a decline to near-baseline values by 12 months. BSAP concentrations increased
by 1 month of treatment and continued to rise more slowly from 6 through 12
months. The maximum increases of BSAP were 45% above baseline in women and 23%
in men. After discontinuation of therapy, BSAP concentrations returned toward
baseline. The increases in formation markers were accompanied by secondary
increases in the markers of bone resorption: urinary N-telopeptide (NTX) and
urinary deoxypyridinoline (DPD), consistent with the physiological coupling of
bone formation and resorption in skeletal remodeling. Changes in BSAP, NTX, and
DPD were lower in men than in women, possibly because of lower systemic
exposure to teriparatide in men.
In the study of patients with glucocorticoid-induced
osteoporosis, the effects of FORTEO on serum markers of bone turnover were
similar to those observed in postmenopausal women with osteoporosis not taking
glucocorticoids.
Pharmacokinetics
Absorption
Teriparatide is absorbed after subcutaneous injection;
the absolute bioavailability is approximately 95% based on pooled data from
20-, 40-, and 80- mcg doses. The rates of absorption and elimination are rapid.
The peptide reaches peak serum concentrations about 30 minutes after subcutaneous
injection of a 20-mcg dose and declines to non-quantifiable concentrations
within 3 hours.
Distribution
Systemic clearance of teriparatide (approximately 62 L/hr
in women and 94 L/hr in men) exceeds the rate of normal liver plasma flow,
consistent with both hepatic and extra-hepatic clearance. Volume of
distribution, following intravenous injection, is approximately 0.12 L/kg.
Intersubject variability in systemic clearance and volume of distribution is 25%
to 50%. The half-life of teriparatide in serum is 5 minutes when administered
by intravenous injection and approximately 1 hour when administered by
subcutaneous injection. The longer half-life following subcutaneous
administration reflects the time required for absorption from the injection
site.
Metabolism And Excretion
No metabolism or excretion studies have been performed
with teriparatide. However, the mechanisms of metabolism and elimination of
PTH(1-34) and intact PTH have been extensively described in published
literature. Peripheral metabolism of PTH is believed to occur by non-specific
enzymatic mechanisms in the liver followed by excretion via the kidneys.
Pediatric Patients
Pharmacokinetic data in pediatric patients are not
available [see WARNINGS AND PRECAUTIONS].
Geriatric Patients
No age-related differences in teriparatide
pharmacokinetics were detected (range 31 to 85 years).
Gender
Although systemic exposure to teriparatide was
approximately 20% to 30% lower in men than women, the recommended dose for both
genders is 20 mcg/day.
Race
The populations included in the pharmacokinetic analyses
were 98.5% Caucasian. The influence of race has not been determined.
Renal Impairment
No pharmacokinetic differences were identified in 11 patients
with mild or moderate renal impairment [creatinine clearance (CrCl) 30 to 72
mL/min] administered a single dose of teriparatide. In 5 patients with severe
renal impairment (CrCl < 30 mL/min), the AUC and T1/2 of teriparatide were
increased by 73% and 77%, respectively. Maximum serum concentration of teriparatide
was not increased. No studies have been performed in patients undergoing
dialysis for chronic renal failure [see Use in Specific Populations].
Hepatic Impairment
No studies have been performed in patients with hepatic
impairment. Nonspecific proteolytic enzymes in the liver (possibly Kupffer
cells) cleave PTH(1-34) and PTH(1-84) into fragments that are cleared from the
circulation mainly by the kidney [see Use in Specific Populations].
Drug Interactions
Digoxin - In a study of 15 healthy people
administered digoxin daily to steady state, a single FORTEO dose did not alter
the effect of digoxin on the systolic time interval (from electrocardiographic
Q-wave onset to aortic valve closure, a measure of digoxin's calcium-mediated
cardiac effect). However, sporadic case reports have suggested that
hypercalcemia may predispose patients to digitalis toxicity. Because FORTEO may
transiently increase serum calcium, FORTEO should be used with caution in patients
taking digoxin [see DRUG INTERACTIONS].
Hydrochlorothiazide - In a study of 20 healthy
people, the coadministration of hydrochlorothiazide 25 mg with teriparatide did
not affect the serum calcium response to teriparatide 40 mcg. The 24-hour urine
excretion of calcium was reduced by a clinically unimportant amount (15%). The
effect of coadministration of a higher dose of hydrochlorothiazide with
teriparatide on serum calcium levels has not been studied [see DRUG
INTERACTIONS].
Furosemide - In a study of 9 healthy people and 17
patients with mild, moderate, or severe renal impairment (CrCl 13 to 72
mL/min), coadministration of intravenous furosemide (20 to 100 mg) with teriparatide
40 mcg resulted in small increases in the serum calcium (2%) and 24-hour urine
calcium (37%) responses to teriparatide that did not appear to be clinically
important [see DRUG INTERACTIONS].
Animal Toxicology
In single-dose rodent studies using subcutaneous
injection of teriparatide, no mortality was seen in rats given doses of 1000 mcg/kg
(540 times the human dose based on surface area, mcg/m²) or in mice given
10,000 mcg/kg (2700 times the human dose based on surface area, mcg/m²).
In a long-term study, skeletally mature ovariectomized
female monkeys (N=30 per treatment group) were given either daily subcutaneous
teriparatide injections of 5 mcg/kg or vehicle. Following the 18-month treatment
period, the monkeys were removed from teriparatide treatment and were observed
for an additional 3 years. The 5 mcg/kg dose resulted in systemic exposures
that were approximately 6 times higher than the systemic exposure observed in
humans following a subcutaneous dose of 20 mcg (based on AUC comparison). Bone
tumors were not detected by radiographic or histologic evaluation in any monkey
in the study.
Clinical Studies
Treatment Of Osteoporosis In Postmenopausal Women
The safety and efficacy of once-daily FORTEO, median
exposure of 19 months, were examined in a double-blind, multicenter,
placebo-controlled clinical study of 1637 postmenopausal women with osteoporosis
(FORTEO 20 mcg, n=541).
All women received 1000 mg of calcium and at least 400 IU
of vitamin D per day. Baseline and endpoint spinal radiographs were evaluated
using the semiquantitative scoring. Ninety percent of the women in the study
had 1 or more radiographically diagnosed vertebral fractures at baseline. The primary
efficacy endpoint was the occurrence of new radiographically diagnosed
vertebral fractures defined as changes in the height of previously undeformed
vertebrae. Such fractures are not necessarily symptomatic.
Effect On Fracture Incidence
New Vertebral Fractures - FORTEO, when taken with
calcium and vitamin D and compared with calcium and vitamin D alone, reduced
the risk of 1 or more new vertebral fractures from 14.3% of women in the
placebo group to 5.0% in the FORTEO group. This difference was statistically significant
(p < 0.001); the absolute reduction in risk was 9.3% and the relative
reduction was 65%. FORTEO was effective in reducing the risk for vertebral
fractures regardless of age, baseline rate of bone turnover, or baseline BMD (see
Table 2).
Table 2: Effect of FORTEO on Risk of Vertebral
Fractures in Postmenopaus al Women with Osteoporosis
Percent of Women With Fracture |
|
FORTEO
(N=444) |
Placebo
(N=448) |
Absolute Risk Reduction (%, 95% CI) |
Relative Risk Reduction (%, 95% CI) |
New fracture ( ≥ 1) |
5.0a |
14.3 |
9.3
(5.5-13.1) |
65
(45-78) |
1 fracture |
3.8 |
9.4 |
|
2 fractures |
0.9 |
2.9 |
|
≥ 3 fractures |
0.2 |
2.0 |
|
ap ≤ 0.001 compared with placebo. |
New Nonvertebral Osteoporotic Fractures - FORTEO
significantly reduced the risk of any nonvertebral fracture from 5.5% in the
placebo group to 2.6% in the FORTEO group (p < 0.05). The absolute reduction
in risk was 2.9% and the relative reduction was 53%. The incidence of new
nonvertebral fractures in the FORTEO group compared with the placebo group was
ankle/foot (0.2%, 0.7%), hip (0.2%, 0.7%), humerus (0.4%, 0.4%), pelvis (0%,
0.6%), ribs (0.6%, 0.9%), wrist (0.4%, 1.3%), and other sites (1.1%, 1.5%),
respectively.
The cumulative percentage of postmenopausal women with
osteoporosis who sustained new nonvertebral fractures was lower in women
treated with FORTEO than in women treated with placebo (see Figure 1).
Figure 1: Cumulative Percentage of Postmenopausal
Women with Osteoporosis Sustaining New Nonvertebral Osteoporotic Fractures
Effect on Bone Mineral Density (BMD)
FORTEO increased lumbar spine BMD in postmenopausal women
with osteoporosis. Statistically significant increases were seen at 3 months
and continued throughout the treatment period. Postmenopausal women with
osteoporosis who were treated with FORTEO had statistically significant increases
in BMD from baseline to endpoint at the lumbar spine, femoral neck, total hip,
and total body (see Table 3).
Table 3: Mean Percent Change in BMD from Baseline to
Endpoint in Postmenopausal Women with Osteoporosis, Treated with FORTEO or
Placebo for a Median of 19 Months
|
FORTEO
N=541 |
Placebo
N=544 |
Lumbar spine BMD |
9.7b |
1.1 |
Femoral neck BMD |
2.8c |
-0.7 |
Total hip BMD |
2.6c |
-1.0 |
Trochanter BMD |
3.5c |
-0.2 |
Intertrochanter BMD |
2.6c |
-1.3 |
Ward's triangle BMD |
4.2c |
-0.8 |
Total body BMD |
0.6c |
-0.5 |
Distal 1/3 radius BMD |
-2.1 |
-1.3 |
Ultradistal radius BMD |
-0.1 |
-1.6 |
aIntent-to-treat analysis, last observation
carried forward.
bp < 0.001 compared with placebo.
cp < 0.05 compared with placebo. |
FORTEO treatment increased lumbar spine BMD from baseline
in 96% of postmenopausal women treated. Seventy-two percent of patients treated
with FORTEO achieved at least a 5% increase in spine BMD, and 44% gained 10% or
more.
Both treatment groups lost height during the trial. The
mean decreases were 3.61 and 2.81 mm in the placebo and FORTEO groups,
respectively.
Bone Histology
The effects of teriparatide on bone histology were
evaluated in iliac crest biopsies of 35 postmenopausal women treated for 12 to
24 months with calcium and vitamin D and teriparatide 20 or 40 mcg/day. Normal
mineralization was observed with no evidence of cellular toxicity. The new bone
formed with teriparatide was of normal quality (as evidenced by the absence of
woven bone and marrow fibrosis).
Treatment To Increase Bone Mass In Men With Primary Or Hypogonadal
Osteoporosis
The safety and efficacy of once-daily FORTEO, median
exposure of 10 months, were examined in a double-blind, multicenter,
placebo-controlled clinical study of 437 men with either primary (idiopathic) or
hypogonadal osteoporosis (FORTEO 20 mcg, n=151). All men received 1000 mg of
calcium and at least 400 IU of vitamin D per day. The primary efficacy endpoint
was change in lumbar spine BMD.
FORTEO increased lumbar spine BMD in men with primary or
hypogonadal osteoporosis. Statistically significant increases were seen at 3
months and continued throughout the treatment period. FORTEO was effective in
increasing lumbar spine BMD regardless of age, baseline rate of bone turnover,
and baseline BMD. The effects of FORTEO at additional skeletal sites are shown
in Table 4.
FORTEO treatment for a median of 10 months increased
lumbar spine BMD from baseline in 94% of men treated. Fifty-three percent of
patients treated with FORTEO achieved at least a 5% increase in spine BMD, and
14% gained 10% or more.
Table 4: Mean Percent Change in BMD from Baseline to
Endpointa in Men with Primary or Hypogonadal Osteoporosis, Treated with FORTEO
or Placebo for a Median of 10 Months
|
FORTEO
N=151 |
Placebo
N=147 |
Lumbar spine BMD |
5.9b |
0.5 |
Femoral neck BMD |
1.5c |
0.3 |
Total hip BMD |
1.2 |
0.5 |
Trochanter BMD |
1.3 |
1.1 |
Intertrochanter BMD |
1.2 |
0.6 |
Ward's triangle BMD |
2.8 |
1.1 |
Total body BMD |
0.4 |
-0.4 |
Distal 1/3 radius BMD |
-0.5 |
-0.2 |
Ultradistal radius BMD |
-0.5 |
-0.3 |
aIntent-to-treat analysis, last observation
carried forward.
bp < 0.001 compared with placebo.
cp < 0.05 compared with placebo. |
Treatment Of Men And Women With Glucocorticoid-Induced Osteoporosis
The efficacy of FORTEO for treating glucocorticoid-induced
osteoporosis was assessed in a randomized, double-blind, active-controlled
trial of 428 patients (19% men, 81% women) aged 22 to 89 years (mean 57 years)
treated with ≥ 5 mg/day prednisone or equivalent for a minimum of 3
months. The duration of the trial was 18 months with 214 patients exposed to
FORTEO. In the FORTEO group, the baseline median glucocorticoid dose was 7.5
mg/day and the median duration of glucocorticoid use was 1.5 years. The mean
(SD) baseline lumbar spine BMD was 0.85 ± 0.13 g/cm² and lumbar spine BMD
Tscore was -2.5 ± 1 (number of standard deviations below the mean BMD value for
healthy adults). A total of 30% of patients had prevalent vertebral fracture(s)
and 43% had prior non-vertebral fracture(s). Â The patients had chronic
rheumatologic, respiratory or other diseases that required sustained glucocorticoid
therapy. All patients received 1000 mg of calcium plus 800 IU of vitamin D supplementation
per day.
Because of differences in mechanism of action (anabolic
vs. anti-resorptive) and lack of clarity regarding differences in BMD as an
adequate predictor of fracture efficacy, data on the active comparator are not
presented.
Effect On Bone Mineral Density (BMD)
In patients with glucocorticoid-induced osteoporosis,
FORTEO increased lumbar spine BMD compared with baseline at 3 months through 18
months of treatment. In patients treated with FORTEO, the mean percent change
in BMD from baseline to endpoint was 7.2% at the lumbar spine, 3.6% at the total
hip, and 3.7% at the femoral neck (p < 0.001 all sites). The relative
treatment effects of FORTEO were consistent in subgroups defined by gender,
age, geographic region, body mass index, underlying disease, prevalent
vertebral fracture, baseline glucocorticoid dose, prior bisphosphonate use, and
glucocorticoid discontinuation during trial.