| Pharmacotherapeutic group: parathyroid hormone, ATC code: H05 AA03. Mechanism of action Preotact contains recombinant human parathyroid hormone which is identical to the full-length native 84-amino acid polypeptide.Physiological actions of parathyroid hormone include stimulation of bone formation by direct effects on bone forming cells (osteoblasts) indirectly increasing the intestinal absorption of calcium and increasing the tubular reabsorption of calcium and excretion of phosphate by the kidney.Pharmacodynamic effects The skeletal effects of parathyroid hormone depend upon the pattern of systemic exposure. Transient elevations in parathyroid hormone levels after subcutaneous injection of Preotact stimulates new bone formation on trabecular and cortical (periosteal and/or endosteal) bone surfaces by preferential stimulation of osteoblastic activity over osteoclastic activity.Effects on serum calcium concentrations Parathyroid hormone is the principal regulator of serum calcium homeostasis. In response to subcutaneous doses of Preotact (100 micrograms parathyroid hormone), serum total calcium levels increase gradually and reach peak concentration (mean increase in 129 patients, 0.15 mmol/l) at approximately 6 to 8 hours after dosing. In general, serum calcium levels return to baseline levels 24 hours after dosing.Based on two placebo-controlled studies involving 2642 postmenopausal osteoporotic women, hypercalcemia was reported in 25.3 % of patients treated with Preotact compared to 4.3 % of placebo-treated patients. The hypercalcemia was transient and was reported most frequently in the first 3 months of treatment. It was managed during the clinical programme by monitoring laboratory values and the use of a pre-specified management algorithm.(see sections 4.3 and 4.4). Clinical efficacy Effect on fracture incidence The pivotal study was an 18-month double-blind, placebo-controlled, phase III study (TOP) of the effect of Preotact on fracture incidence in women with postmenopausal osteoporosis. A total of 2532 patients (1286 Preotact and 1246 placebo), aged 45-94 years (8.1 % 45-54 years and 11.4 % 75 years), were randomised to receive 100 micrograms/day or placebo with daily calcium (700 mg) and vitamin D (400 IU) supplementation. Overall, approximately 19 % of the subjects in each treatment group had at least 1 prevalent vertebral fracture at baseline. The mean baseline lumbar T score was approximately -3.0 in each treatment group.Of the 2532 randomised intention-to-treat (ITT) patients, a total of 59 patients experienced at least one new vertebral fracture, placebo: 42 (3.37 %) Preotact: 17 (1.32 %), p=0.001. Patients in the Preotact treatment group had a 61 % relative risk reduction of a new vertebral fracture at month 18 compared to the patients in the placebo group.To prevent one or more new vertebral fractures, 48 women had to be treated for a median of 18 months for the total population. For patients with pre-existing fractures, number needed to treat (NNT) is 21 patients.There was no significant difference between the treatment groups in the incidence of any non-vertebral clinical fracture: 5.52 % for Preotact vs. 5.86 % for placebo.The most relevant fracture reduction was observed among patients at high risk of fractures such as patients with previous fractures and in patients with a lumbar spine T-score of - 3.Relatively few patients less than 5 years postmenopausal and 45-54 years of age were enrolled in the phase III study (2-3 %). The results for these subjects were not different from the results in the study as a whole.Effect on bone mineral density (BMD) In the pivotal study, Preotact increased BMD in the lumbar spine after 18 months treatment by 6.5 % compared with -0.3 % for placebo (p<0.001). Significant increases in hip BMD (total, femoral neck, trochanter) were observed at study endpoint; 1.0, 1.8 and 1.0 %, respectively, for Preotact versus -1.1, -0.7 and -0.6 % for placebo (p<0.001). Continued treatment for up to 24 months in an open-label extension of this study resulted in a continued increase in BMD. The increase from baseline in lumbar spine and femoral neck BMD was 6.8 % and 2.2 %, respectively in patients treated with Preotact.The effects of Preotact on bone architecture were evaluated using quantitative computed tomography (QCT) and peripheral QCT. Volumetric trabecular BMD at the lumbar spine increased by 38 % over baseline at 18 months. Similarly, volumetric trabecular BMD at the total hip increased by 4.7 %. Similar increases occurred at the femoral neck, trochanter, and intertrochanter. Treatment with Preotact reduced volumetric cortical bone BMD (measured at the distal radius and mid-shaft tibia), while periosteal circumference or indices of cortical bone strength were maintained.In the 24-month alendronate combination therapy study (PaTH), the effects of Preotact on bone architecture were also evaluated using QCT. Volumetric trabecular BMD at the lumbar spine increased by 26, 13, and 11 % (Preotact, Preotact and alendronate and alendronate, respectively) over baseline at 12 months. Similarly, volumetric trabecular BMD at the total hip increased by 9, 6, and 2 %, respectively, in the 3 groups. Treatment of osteoporosis with combination and sequential therapy The PaTH study was a NIH sponsored randomised, placebo-controlled, 2 year, multicenter, double-blind trial of Preotact and alendronate as monotherapy and in combination for the treatment of postmenopausal osteoporosis. Inclusion criterias were; women between 55 and 85 years of age with BMD T-scores below -2.5 or below -2 and at least one additional risk factor for fracture. All women were given calcium (400-500 mg) and vitamin D (400 IU) supplements.A total of 238 postmenopausal women, were randomly assigned to one of the following treatment groups; Preotact (100 micrograms parathyroid hormone), alendronate (10 mg), or the combination of both, and followed for 12 months. In the second year of the study women in the original Preotact group were randomly assigned to receive either alendronate or matching placebo, and women in the other two groups received alendronate.At baseline a total of 165 women (69 %) had a T-score below 2.5, and 112 (47 %) reported at least one fracture after menopause.One year of therapy, showed the following results: The increases in lumbar spine BMD above baseline were similar in the Preotact and combination-therapy groups (6.3 and 6.1 %, respectively), but were somewhat smaller in the alendronate group (4.6 %). Increases in BMD at the total hip were 0.3, 1.9, and 3.0 % for the 3 groups, respectively.At the end of year 2 (12 months after Preotact was discontinued), there was a 12.1 % mean increase in dual energy X-ray absorptiometry (DXA) spine BMD for patients who received alendronate for the second year. For the patients who received placebo during the second year, the mean percent increase was 4.1 % compared to baseline, but had decreased slightly compared to the end of 12 months of Preotact treatment. For the mean change in hip BMD, there was a 4.5 % increase from baseline with one year of alendronate compared to a 0.1 % decrease after one year of placebo.Preotact in combination with hormone replacement therapy (HRT) in 180 postmenopausal women has been shown to significantly increase lumbar spine BMD at 12 months compared with HRT alone (7.1 % vs. 1.1 %, p<0.001). The combination was effective regardless of age, baseline rate of bone turnover, or baseline BMD. | |