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 high238 affinity
cell-surface 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 carboxy-terminal 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 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 T½ 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. Non-specific
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 Postmenopausal 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 |
|
|
| a p ≤ 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 Endpointa
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 |
a Intent-to-treat analysis, last observation
carried forward.
b p < 0.001 compared with placebo.
c p < 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 |
a Intent-to-treat analysis, last observation
carried forward.
b p < 0.001 compared with placebo.
c p < 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, active461 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
T-score 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). 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.
Last updated on RxList: 8/10/2009