CLINICAL PHARMACOLOGY
Mechanism of Action
The action of ibandronate on bone tissue is based on its affinity for hydroxyapatite, which is part of the mineral matrix of bone. Ibandronate inhibits osteoclast activity and reduces bone resorption and turnover. In postmenopausal women, it reduces the elevated rate of bone turnover, leading to, on average, a net gain in bone mass.
Pharmacokinetics
Distribution
Area under the serum ibandronate concentrations versus time curve increases in a dose-proportional manner after administration of 2 mg to 6 mg by intravenous injection. After administration, ibandronate either rapidly binds to bone or is excreted into urine. In humans, the apparent terminal volume of distribution is at least 90 L, and the amount of dose removed from the circulation into the bone is estimated to be 40% to 50% of the circulating dose. In vitro protein binding in human serum was approximately 86% over an ibandronate concentration range of 20 to 2000 ng/mL (approximate range of maximum serum ibandronate concentrations upon intravenous bolus administration) in one study.
Metabolism
There is no evidence that ibandronate is metabolized in humans. Ibandronate does not inhibit human P450 1A2, 2A6, 2C9, 2C19, 2D6, 2E1, and 3A4 isozymes in vitro.
Elimination
The portion of ibandronate that is not removed from the circulation via bone absorption is eliminated unchanged by the kidney (approximately 50% to 60% of the administered intravenous dose).
The plasma elimination of ibandronate is multiphasic. Its renal clearance and distribution into bone accounts for a rapid and early decline in plasma concentrations, reaching 10% of Cmax within 3 or 8 hours after intravenous or oral administration, respectively. This is followed by a slower clearance phase as ibandronate redistributes back into the blood from bone. The observed apparent terminal half-life for ibandronate is generally dependent on the dose studied and on assay sensitivity. The observed apparent terminal half-life for intravenous 2 and 4 mg ibandronate after 2 hours of infusion ranges from 4.6 to 15.3 hours and 5 to 25.5 hours, respectively.
Following intravenous administration, total clearance of ibandronate is low, with average values in the range 84 to 160 mL/min. Renal clearance (about 60 mL/min in healthy postmenopausal women) accounts for 50% to 60% of total clearance and is related to creatinine clearance. The difference between the apparent total and renal clearances likely reflects bone uptake of the drug.
Special Populations
Pediatrics
The pharmacokinetics of ibandronate has not been studied in patients <18 years of age.
Gender
The pharmacokinetics of ibandronate is similar in both men and women.
Geriatric
Since ibandronate is not known to be metabolized, the only difference in ibandronate elimination for geriatric patients versus younger patients is expected to relate to progressive age-related changes in renal function (see Special Populations: Renal Impairment).
Race
Pharmacokinetic differences due to race have not been studied.
Renal Impairment
Renal clearance of ibandronate in patients with various degrees of renal impairment is linearly related to creatinine clearance (CLcr).
Following a single dose of 0.5 mg ibandronate by intravenous administration, patients with CLcr 40 to 70 mL/min had 55% higher exposure (AUC∞) than the exposure observed in subjects with CLcr >90 mL/min. Patients with CLcr <30 mL/min had more than a two-fold increase in exposure compared to the exposure for healthy subjects (see DOSAGE AND ADMINISTRATION: Patients with Renal Impairment).
Hepatic Impairment
No studies have been performed to assess the pharmacokinetics of ibandronate in patients with hepatic impairment since ibandronate is not metabolized in the human liver.
Drug Interactions
Ibandronate does not undergo hepatic metabolism and does not inhibit the hepatic cytochrome P450 system. Ibandronate is eliminated by renal excretion. Based on a rat study, the ibandronate secretory pathway does not appear to include known acidic or basic transport systems involved in the excretion of other drugs.
Melphalan/Prednisolone
A pharmacokinetic interaction study in multiple myeloma patients demonstrated that intravenous melphalan (10 mg/m2) and oral prednisolone (60 mg/m2) did not interact with 6 mg ibandronate upon intravenous coadministration. Ibandronate did not interact with melphalan or prednisolone.
Tamoxifen
A pharmacokinetic interaction study in healthy postmenopausal women demonstrated that there was no interaction between oral 30 mg tamoxifen and intravenous 2 mg ibandronate.
Pharmacodynamics
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 a 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. While osteoporosis occurs in both men and women, it is most 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 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.
In studies of postmenopausal women, BONIVA Injection at doses of 0.5 mg to 3 mg produced biochemical changes indicative of inhibition of bone resorption, including decreases of biochemical markers of bone collagen degradation (cross-linked C-telopeptide of Type I collagen [CTX]). Changes in markers of bone formation (osteocalcin) were observed later than changes in resorption markers, as expected, due to the coupled nature of bone resorption and formation.
Year 1 results from an efficacy and safety study comparing BONIVA Injection 3 mg every 3 months and BONIVA 2.5 mg daily oral tablet demonstrated that both dosing regimens significantly suppressed serum CTX levels at Months 3, 6, and 12. The median pre-dose or trough serum CTX levels in the ITT population reached a nadir of 57% (BONIVA Injection) and 62% (BONIVA 2.5 mg tablets) below baseline values by Month 6, and remained stable at Month 12 of treatment.
Clinical Studies
Daily Oral Tablets
The effectiveness and safety of BONIVA daily oral tablets were demonstrated in a randomized, double-blind, placebo-controlled, multinational study (Treatment Study) of 2946 women aged 55 to 80 years, who were on average 21 years postmenopause, who had lumbar spine bone mineral density (BMD) 2 to 5 SD below the premenopausal mean (T-score) in at least one vertebra [L1-L4], and who had one to four prevalent vertebral fractures. BONIVA was evaluated at oral doses of 2.5 mg daily and 20 mg intermittently. The main outcome measure was the occurrence of new radiographically diagnosed, vertebral fractures after 3 years of treatment. The diagnosis of an incident vertebral fracture was based on both qualitative diagnosis by the radiologist and quantitative morphometric criterion. The morphometric criterion required the dual occurrence of two events: a relative height ratio or relative height reduction in a vertebral body of at least 20%, together with at least a 4 mm absolute decrease in height. All women received 400 IU vitamin D and 500 mg calcium supplementation per day.
Quarterly IV Injection
The effectiveness and safety of BONIVA Injection 3 mg once every 3 months were demonstrated in a randomized, double-blind, multinational, noninferiority study (DIVA Study) in 1358 women with postmenopausal osteoporosis (L2-L4 lumbar spine BMD, T score below -2.5 SD at baseline). The control group received BONIVA 2.5 mg daily oral tablets. The primary efficacy parameter was the relative change from baseline to 1 year of treatment in lumbar spine BMD, which was compared between the intravenous injection and the daily oral treatment groups. All patients received 400 IU vitamin D and 500 mg calcium supplementation per day.
Effect on Vertebral Fracture
BONIVA 2.5 mg daily oral tablet significantly reduced the incidence of new vertebral and of new and worsening vertebral fractures (Daily Oral Tablet – Treatment Study). Over the course of the 3-year study, the risk for vertebral fracture was 9.6% in the placebo-treated women and 4.7% in the women treated with BONIVA 2.5 mg daily oral tablet (p<0.001) (see Table 1). In an unapproved regimen, intermittent oral administration of 20 mg BONIVA, involving a 9- to 10-week drug-free interval, produced a statistically significant reduction (50%) in the incidence of new vertebral fractures, similar to that seen with the daily oral 2.5 mg regimen.
Table 1 Effect of BONIVA Daily Oral Tablet on the Incidence of Vertebral Fracture in the 3-Year Osteoporosis Treatment StudyThe endpoint value is the value at the study's last time point, 3 years, for all patients who had a fracture identified at that time; otherwise, the last postbaseline value prior to the study's last time point is used. | Proportion of Patients with Fracture (%) |
|---|
| Placebo
n=975 | BONIVA
2.5 mg
Daily
n=977 | Absolute Risk Reduction
(%)
95% CI | Relative Risk Reduction
(%)
95% CI |
|---|
| New Vertebral Fracture | 9.6 | 4.7 | 4.9 | 52 p=0.0003 vs. placebo |
| 0-3 Year | | | (2.3, 7.4) | (29, 68) |
| New and Worsening Vertebral Fracture | 10.4 | 5.1 | 5.3 | 52 |
| 0-3 Year | | | (2.6, 7.9) | (30, 67) |
| Clinical (Symptomatic) Vertebral Fracture | 5.3 | 2.8 | 2.5 | 49 |
| 0-3 Year | | | (0.6, 4.5) | (14, 69) |
Effect on Nonvertebral Fractures
There was a similar number of nonvertebral osteoporotic fractures at 3 years reported in women treated with BONIVA 2.5 mg daily oral tablet [9.1%, (95% CI: 7.1%, 11.1%)] and placebo [8.2%, (95% CI: 6.3%, 10.2%)]. The two treatment groups were also similar with regard to the number of fractures reported at the individual non-vertebral sites: pelvis, femur, wrist, forearm, rib, and hip (Daily Oral Tablet - Treatment Study).
Effect on Bone Mineral Density (BMD)
Daily Oral Tablet - Treatment Study: BONIVA 2.5 mg daily oral tablet significantly increased BMD at the lumbar spine and hip relative to treatment with placebo. In the 3-year osteoporosis treatment study, BONIVA 2.5 mg daily oral tablet produced increases in lumbar spine BMD that were progressive over 3 years of treatment and were statistically significant relative to placebo at 6 months and at all later time points. Lumbar spine BMD increased by 6.4% after 3 years of treatment with BONIVA 2.5 mg daily oral tablet compared with 1.4% in the placebo group. Table 2 displays the significant increases in BMD seen at the lumbar spine, total hip, femoral neck, and trochanter compared to placebo. Thus, overall BONIVA 2.5 mg daily oral tablet reverses the loss of BMD, a central factor in the progression of osteoporosis.
Table 2 Mean Percent Change in BMD from Baseline to Endpoint in Patients Treated with BONIVA 2.5 mg Daily Oral Tablet or Placebo in the 3-Year Osteoporosis Treatment StudyThe endpoint value is the value at the study's last time point, 3 years, for all patients who had BMD measured at that time; otherwise the last postbaseline value prior to the study's last time point is used. | Placebo | BONIVA 2.5 mg |
|---|
| Lumbar Spine | 1.4
(n=693) | 6.4
(n=712) |
| Total Hip | -0.7
(n=638) | 3.1
(n=654) |
| Femoral Neck | -0.7
(n=683) | 2.6
(n=699) |
| Trochanter | 0.2
(n=683) | 5.3
(n=699) |
Quarterly IV Injection– DIVA Study: In the ITT efficacy analysis, the least-squares mean increase at 1 year in lumbar spine BMD in patients (n=429) treated with BONIVA Injection 3 mg once every 3 months (4.5%) was statistically superior to that in patients (n=434) treated with daily oral tablets (3.5%). The mean difference between groups was 1.05% (95% CI: 0.53%, 1.57%; p<0.001; see Figure 1). The mean increases from baseline in total hip BMD at 1 year were 2.1% in the BONIVA Injection 3 mg once every 3 months group and 1.5% in the BONIVA 2.5 mg daily oral tablet group. Consistently higher BMD increases at the femoral neck and trochanter were also observed following BONIVA Injection 3 mg once every 3 months compared to BONIVA 2.5 mg daily oral tablet.
Figure 1 Mean Percent Change (95% CI) from Baseline in Lumbar Spine BMD at One Year in Patients Treated with BONIVA 2.5 mg Daily Oral Tablet or BONIVA Injection 3 mg Once Every 3 Months
Bone Histology
The effects of BONIVA 2.5 mg daily oral tablet on bone histology were evaluated in iliac crest biopsies from 16 women after 22 months of treatment and 20 women after 34 months of treatment. The histological analysis of bone biopsies showed bone of normal quality and no indication of osteomalacia or a mineralization defect.
The histological analysis of bone biopsies after 22 months of treatment with 3 mg intravenous ibandronate every 3 months (n=30) or 23 months of treatment with 2 mg intravenous ibandronate every 2 months (n=27) in women with postmenopausal osteoporosis showed bone of normal quality and no indication of a mineralization defect.
Animal Pharmacology
Animal studies have shown that ibandronate is an inhibitor of osteoclast-mediated bone resorption. In the Schenk assay in growing rats, ibandronate inhibited bone resorption and increased bone volume, based on histologic examination of the tibial metaphyses. There was no evidence of impaired mineralization at the highest dose of 5 mg/kg/day (subcutaneously), which is 1000 times the lowest antiresorptive dose of 0.005 mg/kg/day in this model, and 5000 times the optimal antiresorptive dose of 0.001 mg/kg/day in the aged ovariectomized rat. This indicates that BONIVA Injection administered at a therapeutic dose is unlikely to induce osteomalacia.
Long-term daily or intermittent administration of ibandronate to ovariectomized rats or monkeys was associated with suppression of bone turnover and increases in bone mass. Vertebral BMD, trabecular density, and biomechanical strength were increased dose-dependently in rats and monkeys, at doses up to 8 to 4 times the human intravenous dose of 3 mg every 3 months, based on cumulative dose normalized for body surface area (mg/m2) and AUC comparison, respectively. Ibandronate maintained the positive correlation between bone mass and strength at the ulna and femoral neck. New bone formed in the presence of ibandronate had normal histologic structure and did not show mineralization defects.
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