Bone lesion absorbed dose profiles in patients with metastatic prostate cancer treated with molecular radiotherapy

OBJECTIVE

The aim of this study was to calculate the range of absorbed doses that could potentially be delivered by a variety of radiopharmaceuticals and typical fixed administered activities used for bone pain palliation in a cohort of patients with metastatic castration-resistant prostate cancer (mCRPC). The methodology for the extrapolation of the biodistribution, pharmacokinetics and absorbed doses from a given to an alternative radiopharmaceutical is presented.

METHODS

Sequential single photon emission CT images from 22 patients treated with 5 GBq of 186Re-HEDP were used to extrapolate the time-activity curves for various radiopharmaceuticals. Cumulated activity distributions for the delivered and extrapolated treatment plans were converted into absorbed dose distributions using the convolution dosimetry method. The lesion absorbed doses obtained for the different treatments were compared using the patient population distributions and cumulative dose-volume histograms.

RESULTS

The median lesion absorbed doses across the patient cohort ranged from 2.7 Gy (range: 0.6-11.8 Gy) for 1100 MBq of 166Ho-DOTMP to 21.8 Gy (range: 4.5-117.6 Gy) for 150 MBq of 89Sr-dichloride. 32P-Na3PO4, 153Sm-EDTMP, 166Ho-DOTMP, 177Lu-EDTMP and 188Re-HEDP would have delivered 41, 32, 85, 20 and 64% lower absorbed doses, for the typical administered activities as compared to 186Re-HEDP, respectively, whilst 89Sr-dichloride would have delivered 25% higher absorbed doses.

CONCLUSION

For the patient cohort studied, a wide range of absorbed doses would have been delivered for typical administration protocols in mCRPC. The methodology presented has potential use for emerging theragnostic agents. Advances in knowledge: The same patient cohort can receive a range of lesion absorbed doses from typical molecular radiotherapy treatments for patients with metastatic prostate cancer, highlighting the need to establish absorbed dose response relationships and to treat patients according to absorbed dose instead of using fixed administered activities.

Development of bone seeker radiopharmaceuticals by Scandium-47 and estimation of human absorbed dose

In this study labeling EDTMP (ethylenediamine tetra(methylene phosphonic acid)) and HEDP (Hydroxyethylidene-1, 1-Diphosphonic Acid) as the carrier ligands with Scandium-47 were investigated. The biokinetics of the bone seeking of labeled ligands with Scandium-47 were assessed by measuring the skeletal absorbed dose and then the mice data extrapolated to human absorbed dose and compared with the ^186/188Rhenium-HEDP, ¹⁵³Samarium-EDTMP dosimetry data estimated by other researchers. Because the availability of ⁴⁷Sc was limited we performed some preliminary studies using ⁴⁶Sc.

Adsorption on apatitic calcium phosphates for drug delivery: interaction with bisphosphonate molecules

Bisphosphonates (BPs) are well established as an important class of drugs for the treatment and prevention of several bone disorders including osteoporosis. This work investigated the interaction of two bisphosphonates, risedronate and tiludronate, with several apatitic supports, a well-crystallised hydroxyapatite (HA) and nanocrystalline apatites with varying maturation times, chemical composition and surface characteristics. The purpose was to fully understand the adsorption mechanism and desorption process, by the evaluation of the effect of several physicochemical parameters (temperature, pH and concentration of calcium and phosphate ions). Whatever the nature of the BP and the structure and composition of the apatite, the adsorption of such anti-resorptive agents can be well described as an ion exchange-reaction between phosphates species on the apatitic surface and BP molecules in solution. However, the parameters of adsorption can vary depending on the physicochemical conditions of the adsorption reaction. In addition, the structure and composition of the apatitic surface also influence the adsorption properties. Finally, BPs molecules are slowly released from apatitic supports, because most of the adsorbed molecules are irreversibly bound and not spontaneously released by dilution or simple washing. Moreover, similar to their adsorption, the release of bisphosphonates is strongly affected not only by the chemical properties of the molecule, but also by the chemical and structural characteristics of the apatitic substrates. The understanding of the adsorption and release processes provides fundamental tools for the development of drug delivery systems using apatite materials.

Anti-reabsorptive agents in women with osteoporosis: determining statistical equivalence according to evidence-based methods

BACKGROUND

In the present study, we undertook an equivalence analysis on the effectiveness of the main anti-reabsorptive agents indicated for women with osteoporosis.

METHODS

Our methodology was a combination of meta-analysis (both pair-wise meta-analysis and network meta-analysis) and equivalence testing. The end-point was the incidence on new vertebral fractures. The anti-reabsorptive agents examined included alendronate, zoledronate, ibandronate, risedronate, and denosumab.

RESULTS

Our analysis involved nine randomized trials. Ten head-to-head indirect comparisons were examined through network meta-analysis and the respective values of RR were estimated. The 95 % confidence intervals for RR remained within the interval of a relative ±40 % variation for all comparisons that involved alendronate, risedronate, ibandronate, and denosumab. In contrast, the comparisons involving zoledronate satisfied a post hoc margin up to ±67 %.

CONCLUSION

Our results confirm that most of these anti-reabsorptive drugs (namely, alendronate, risedronate, ibandronate, and denosumab) are equivalent according to reasonable equivalence margins.

In vitro disintegration studies of weekly generic and branded risedronate sodium formulations available in Canada

OBJECTIVE

The aim of this study was to evaluate the in vitro disintegration of the five newly available Canadian generic risedronate 35 mg tablets compared to the innovator (branded) product, ACTONEL * *ACTONEL is a registered trade name of Warner Chilcott Company, LLC. (risedronate sodium) 35 mg.

RESEARCH DESIGN AND METHODS

Tablets were inspected for colour and appearance. Disintegration times were determined using United States Pharmacopeia 33 (USP33-NF 28) methods. Disintegration onset time was also evaluated.

RESULTS

The mean disintegration onset time values for the generic risedronate 35 mg tablets ranged from 2 to 29 seconds, and the mean disintegration completion times ranged from 81 to 260 seconds. The mean disintegration onset and completion time values for the ACTONEL 35 mg tablets were 23 and 43 seconds respectively. Four out of the five generic tablets tested had shorter disintegration onset times than the branded product; two of the generic tablet products had very fast disintegration onset times i.e. 2-3 seconds. Disintegration completion time for all five generic products tested was longer than that observed for the branded product; two generic products had disintegration completion time values five to six times longer than the branded product.

CONCLUSIONS

Differences in the in vitro disintegration times were observed between the generic risedronate 35 mg tablets commercially available in Canada and the branded product, ACTONEL. The rapid disintegration onset times of two generic products may be important as this could increase the possibility of drug exposure in both the mouth and the esophagus during swallowing, resulting in unwanted localized irritation. However, it should be noted that an in vitro/in vivo correlation has not been established. Until such studies are completed it may be important to be aware of such in vitro disintegration differences when evaluating patients with newly presenting upper gastrointestinal complaints upon being switched from the branded product to generic formulations.

Differences in persistence, safety and efficacy of generic and original branded once weekly bisphosphonates in patients with postmenopausal osteoporosis: 1-year results of a retrospective patient chart review analysis

The objective of this study was to compare the changes on bone mineral density, and the effects on persistence and adverse events in patients treated for postmenopausal osteoporosis with generic alendronate or with branded alendronate (Fosamax®) or branded risedronate (Actonel®) once weekly. In this retrospective patient chart analysis, we reviewed the 1-year observational treatment results for 186 women (ITT population) with postmenopausal osteoporosis. Patients from our outpatient department, who had started with once-weekly bisphosphonate therapy between 36 and at least 12 months before this chart review, were included in this comparative three-arm study according to their treatment: A, Generic Alendonate 70 mg products; B, Branded Alendronate (Fosamax®) 70 mg once weekly and C, Branded Risedronate (Actonel®) 35 mg once weekly. All patients received basic therapy with 1,200 mg calcium and 800 IU vitamin D per day. Patient’s bone mineral density (BMD) at lumbar spine and total hip was below −2.5 T-score, and they were with or without prevalent vertebral and non-vertebral fractures. Data analysis regarding the 186 patients shows an average increase in LS-BMD after 12 months of 2.8, 5.2 and 4.8% for the groups A, B and C, respectively. The respective mean changes at total hip were 1.5, 2.9, and 3.1%. At both sites, the mean increases in BMD were not different between the two groups receiving branded bisphosphonates (B, C) but for both were significantly higher than for the group treated with generic alendronate (A). At 12 months, 68% of group A, 84% of group B and 94% of group C were still on bisphosphonate therapy. The persistence of patients treated with generic alendronate was significantly lower as compared to each of the two with branded bisphosphonate-treated groups. The total numbers of patients reporting gastrointestinal adverse events were 32, 15 and 9 for group A, group B, and group C, respectively. Significantly lower increases of lumbar spine and total hip BMD with generic alendronate once weekly as compared to the two branded bisphosphonate originals (Fosamax®, Actonel®) were observed. The reasons for the 40–50% lower BMD increase rates when using the generic compounds are not known yet. At least in part the lower efficacy can be explained by a significantly lower degree of persistence with generic alendronate, which could be related to a higher incidence of gastrointestinal adverse events. Other reasons could be lower bioavailability or potency of generic alendronate.

Visualizing mineral binding and uptake of bisphosphonate by osteoclasts and non-resorbing cells

Bisphosphonates (BPs) target bone due to their high affinity for calcium ions. During osteoclastic resorption, these drugs are released from the acidified bone surface and taken up by osteoclasts, where they act by inhibiting the prenylation of small GTPases essential for osteoclast function. However, it remains unclear exactly how osteoclasts internalise BPs from bone and whether other cells in the bone microenvironment can also take up BPs from the bone surface. We have investigated this using a novel fluorescently-labelled alendronate analogue (FL-ALN), and by examining changes in protein prenylation following treatment of cells with risedronate (RIS). Confocal microscopic analysis showed that FL-ALN was efficiently internalised from solution or from the surface of dentine by resorbing osteoclasts into intracellular vesicles. Accordingly, unprenylated Rap1A accumulated to the same extent whether osteoclasts were cultured on RIS-coated dentine or with RIS in solution. By contrast, J774 macrophages internalised FL-ALN and RIS from solution, but took up comparatively little from dentine, due to their inability to resorb the mineral. Calvarial osteoblasts and MCF-7 tumour cells internalised even less FL-ALN and RIS, both from solution and from the surface of dentine. Accordingly, the viability of J774 and MCF-7 cells was drastically reduced when cultured with RIS in solution, but not when cultured on dentine pre-coated with RIS. However, when J774 macrophages were co-cultured with rabbit osteoclasts, J774 cells that were adjacent to resorbing osteoclasts frequently internalised more FL-ALN than J774 cells more distant from osteoclasts. This was possibly a result of increased availability of BP to these J774 cells due to transcytosis through osteoclasts, since FL-ALN partially co-localised with trancytosed, resorbed matrix protein within osteoclasts. In addition, J774 cells occupying resorption pits internalised more FL-ALN than those on unresorbed surfaces. These data demonstrate that osteoclasts are able to take up large amounts of BP, due to their ability to release the BP from the dentine surface during resorption. By contrast, non-resorbing cells take up only small amounts of BP that becomes available due to natural desorption from the dentine surface. However, BP uptake by non-resorbing cells can be increased when cultured in the presence of resorbing osteoclasts.

Effect of administration site in the gastrointestinal tract on bioavailability of poorly absorbed drugs taken after a meal

Food-drug interactions may reduce the bioavailability of drugs taken after meals (negative food effect). In order to develop pharmaceutical technologies that overcome this problem, the effect of administration site within the gastrointestinal tract on the bioavailability of several model drugs was examined in rats. Bioavailability after oral administration to fed animals was one-fifth to one-tenth of that in the fasted animals because of interactions between drugs and large amounts of food components remaining in the stomach. This strong negative food effect was reduced when drugs were administered directly into any site of the small intestine. Bioavailability was maximized when the drug administration site was the middle small intestine. On the other hand, intracolonic administration did not result in the reduction of the negative food effect. Site-specific drug delivery to the middle small intestine could be a useful approach for reducing the negative food effect on drug absorption with maximized bioavailability.

Risedronate for prevention and treatment of osteoporosis in postmenopausal women

Risedronate sodium is an N-containing bisphosphonate that has been approved for the prevention and treatment of osteoporosis in postmenopausal women. An increase in the rate of bone remodelling is a regular feature of oestrogen withdrawal during the menopausal transition, but excessive remodelling leads to bone fragility. Risedronate and similar compounds reduce the rate of bone remodelling by suppressing the action of osteoclasts. The antifracture efficacy of risedronate is impressive. In large clinical trials of postmenopausal women with osteoporosis-related fracture(s) at entry, the risk of incident vertebral and non-vertebral fractures was reduced by approximately 40%. In older women at risk for hip fracture, incident hip fractures were also reduced by approximately 40%. Antifracture efficacy develops within the first 6 months, and treatment has been followed for as long as 5 years without deleterious effects on bone. We await reports of experience with risedronate in 'real-world' cases of greater complexity (i.e., in patients with co-morbidities and medications that would have excluded them from published clinical trials).

Esophageal transit of the weekly film-coated risedronate (Actonel®) placebo tablet in subjects with Kyphosis

Risedronate sodium is a pyridinyl bisphosphonate of proven effectiveness for the treatment and prevention of osteoporosis and Paget's disease of the bone. The aim of this study was to compare the esophageal transit and gastric emptying of the placebo film-coated risedronate tablet when taken with 50 or 120 mL of water in subjects with Kyphosis. A total of 23 patients with radiologically documented osteoporosis participated in a single-center, open-label, crossover gamma scintigraphy study. The mean esophageal transit times were 15.6 s (50 mL) and 12.0 s (120 mL) and the mean gastric emptying half-times were 20.5 min (50 mL) and 14.3 min (120 mL). There was no relationship between the degree of Kyphosis measured from lateral standing radiographs and the esophageal transit time. This study demonstrated that even when taken with a minimal volume of water the esophageal transit and gastric emptying of the film-coated 35 mg weekly risedronate placebo tablet was similar in kyphotic subjects to previously obtained results from healthy control subjects.

Preparation and evaluation of floating risedronate sodium Gelucire 39/01 matrices

Incorporation of bisphosphonates in the lipid reduces gastric irritation. Only gastric retention with sustained release allows the drug to reach the duodenum and jejunum and improves the availability of bisphosphonates. Risedronate sodium and Gelucire 39/01 floating matrices were prepared using melt solidification. The sustained release floating matrices were evaluated for in vitro and in vivo floating ability and in vitro drug release. Ageing of the matrices was studied by differential scanning calorimetry, hot stage polarizing microscopy, scanning electron microscopy and in vitro drug release. Ageing causes changes in the crystal structure of Gelucire, which is responsible for an increase in drug release.

Antiresorption therapy and reduction in fracture susceptibility in the osteoporotic elderly patient: open study

The identification of risk factors for osteoporosis has been an essential step towards the understanding of the onset of the disease as well as of the osteoporosis-related fractures due to bone fragility. The present study has been aimed at assessing whether a correlation may exist between the increment in bone mass, consequent to an antiresorption therapy, and the reduction in the incidence of fractures. Moreover, the possibility that such a reduction might result from the action of other factors, such as the changes in bone microstructure, has been investigated. A total of 2,000 osteoporotic women (mean age: 68 +/- 9 years) were enrolled in the study and divided at random into 4 treatment groups. Each group received one of the following treatments: Alendronate 10 mg/daily (1,000 patients), Clodronate 100 mg/weekly i.m. (800 patients), Risedronate 5 mg/dailt (100 patients), and Raloxifene 60 mg/daily (100 patients). Clinical evaluation was based on bone mineral density (BMD) assay on lumbar vertebrae (L1-L4) by means of a DEXA (Lunar DPX) mineralometer, as well as on the incidence of fractures following both 12- and 24-month treatment periods. The results showed an overlapping pattern in patients treated with Alendronate or Risedronate, namely a significant increment in BMD after a 24-month treatment period, whereas such an increment in BMD was less evident in patients receiving either Clodronate or Risedronate after a 24-month treatment period. In addition, a total of 18 osteoporosis-related fractures were observed during the entire study period; 10 out of 18 fractures occurred in the Alendronate treated group, whereas the remaining 8 fractures were observed in the Clodronate treated group. Fourteen fractures were detected in patients over 80-year old, whereas the remaining 4 occurred in patients aged from 70 to 79 years and appeared to be independent of both the T-score assigned and the BMD increment obtained as a result of the therapy. Such findings suggest that the plain monitoring of BMD appears not to be adequate to anticipate clearly the danger of the probable onset of additional fractures, while the higher incidence of fractures in patients over 80-year old evidences that "old age" has to be considered the most serious risk factor for osteoporosis, since it is also the real responsible factor for changes taking place in bone microstructure.

Clinical trial of risedronate in Japanese volunteers: single and multiple oral dose studies

The tolerability and pharmacokinetics of risedronate after a single oral administration and during multiple oral administrations were examined in healthy adult male volunteers. In the single dose study, the dose was increased gradually from 1 mg to 2.5, 5, 10, or 20 mg. Subsequently, risedronate was given by multiple administration, 5 mg per dosing, once daily, for 7 days. The observed adverse events, whose causality was possibly related or unknown, included headache, diarrhea, increased body temperature, increased CK-BB, and increased urinary Beta(2)-microglobulin excretion rate. However, none of these adverse events was clinically significant. The results thus showed that risedronate was well tolerated when delivered as a single administration of up to 20 mg or as a multiple administration of up to 5 mg/day. In the multiple dose study, changes in urinary deoxypyridinoline suggested the bone antiresorptive activity of risedronate. In the single dose study, AUC and C(max), after the administration of risedronate at 1, 2.5, 5, 10, and 20 mg, increased dose dependently, and the T(max), t(1/2), and urinary excretion rates were nearly constant. Therefore, the pharmacokinetic profile of risedronate was considered to show linearity in a dosage range of up to 20 mg. Furthermore, the results obtained in the multiple administration study indicated that the plasma concentrations of risedronate reached a steady state on day 4 of administration. The plasma concentrations of risedronate after the administration of 2.5 mg risedronate to the Japanese population were nearly comparable to the serum concentrations after the administration of 5 mg risedronate to the United Kingdom study population.

Preparation of 1‐hydroxyethylidene‐1,1‐diphosphonic acid‐intercalated layered double hydroxide and its physicochemical properties

The intercalation of 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), which is a drug for osteoporosis, in layered double hydroxide (LDH) was examined with the goal of developing a novel drug delivery system (DDS) of HEDP. To prevent side reactions, the intercalation reaction was carried out at 0 degrees C, and at pH 4-6. The uptake of HEDP was determined as 3.5 mmol x g(-1) of LDH, and the interlayer distance increased from 7.8 to 13 A. The HEDP-release profiles into K(2)CO(3) aqueous solution and into various buffer solutions were also examined.

Therapeutic efficiency of rhenium-188-HEDP in human prostate cancer skeletal metastases

Rhenium-188-HEDP ((188)Re-HEDP) is a new and attractive radiopharmaceutical for the treatment of metastatic bone pain. As a product of (188)W/(188)Re generator, it is convenient for clinical therapeutic use with a short physical half-life of 16.9 h and a maximal beta-energy of 2.1 MeV. We investigated the effect of (188)Re-HEDP on pain relief, analgesic intake and impairment of bone marrow function in 27 patients with bone metastases induced from prostate cancer. All patients were interviewed using a standardised set of questions before, and after therapy for 12 weeks. The patients were treated with 2700-3459 MBq of (188)Re-HEDP. Blood samples were taken weekly for 12 weeks, and a blood count was performed. Patients described an improvement on the Karnofsky performance scale from 74+/-7 to 85+/-9% 12 weeks after therapy (P=0.001). The pain score showed a maximum decrease from 44+/-18 to 27+/-20% in the third to the eight week after therapy (P=0.009). Seventy-six percent of the patients described a pain relief without increase of analgesic intake. Twenty percent of the patients could discontinue their analgesics and were pain free. Mean platelet count decreased from (286+/-75)*10(3) microl(-1) to (215+/-92)*10(3) microl(-1), and mean leucocyte count from (7.7+/-1.5)*10(3) microl(-1) to (6.0+/-1.9)*10(3) microl(-1) in the second to the fourth week after therapy. The maximal differences between the values of platelets and leucocytes before and after therapy were not statistically significant (P=0.021 and 0.094). In conclusion, (188)Re-HEDP is an effective radiopharmaceutical used in the palliative treatment of metastatic bone pain in prostate cancer and shows minimal bone marrow toxicity.

A model-based method for the prediction of whole-body absorbed dose and bone marrow toxicity for 186Re-HEDP treatment of skeletal metastases from prostate cancer

In high-activity rhenium-186 hydroxyethylidene diphosphonate ((186)Re-HEDP) treatment of bone metastatic disease from prostate cancer the dose-limiting factor is haematological toxicity. In this study, we examined the correlation of the injected activity and the whole-body absorbed dose with treatment toxicity and response. Since the best response is likely to be related to the maximum possible injected activity limited by the whole-body absorbed dose, the relationship between pre-therapy biochemical and physiological parameters and the whole-body absorbed dose was studied to derive an algorithm to predict the whole-body absorbed dose prior to injection of the radionuclide. The whole-body retention of radioactivity was measured at several time points after injection in a cohort of patients receiving activities ranging between 2,468 MBq and 5,497 MBq. The whole-body absorbed dose was calculated by fitting a sequential series of exponential phases to the whole-body time-activity data and by integrating this fit over time to obtain the whole-body cumulated activity. This was then converted to absorbed dose using the Medical Internal Radiation Dose (MIRD) committee methodology. Treatment toxicity was estimated by the relative decrease in white cell (WC) and platelet (Plt) counts after the injection of the radionuclide, and by their absolute nadir values. The criterion for a treatment response was a 50% or greater decrease in prostate-specific antigen (PSA) value lasting for 4 weeks. Alkaline phosphatase (AlkPh), chromium-51 ethylene diamine tetra-acetate ((51)Cr-EDTA) clearance rate and weight were measured before injection of the radionuclide. The whole-body absorbed dose showed a significant correlation with WC and Plt toxicity ( P=0.005 and 0.003 for the relative decrease and P=0.006 and 0.003 for the nadir values of WC and Plt counts respectively) in a multivariate analysis which included injected activity, whole-body absorbed dose, pre-treatment WC and Plt baseline counts, PSA and AlkPh values, and the pre-treatment Soloway score. The injected activity did not show any correlation with WC or Plt toxicity, but it did correlate with PSA response ( P=0.005). These results suggest that the administration of higher activities would be likely to generate a better response, but that the quantity of activity that can be administered is limited by the whole-body absorbed dose. We have derived and evaluated a model that estimates the whole-body absorbed dose on an individual patient basis prior to injection. This model uses the level of injected activity and pre-injection measurements of AlkPh, weight and (51)Cr-EDTA clearance. It gave good estimates of the whole-body absorbed dose, with an average difference between predicted and measured values of 15%. Furthermore, the whole-body absorbed dose predicted using this algorithm correlated with treatment toxicity. It could therefore be used to administer levels of activity on a patient-specific basis, which would help in the optimisation of targeted radionuclide therapy. We believe that algorithms of this kind, which use pre-injection biochemical and physiological measurements, could assist in the design of escalation trials based on a toxicity-limiting whole-body absorbed dose, rather than using the more conventional activity escalation approach.

Dosimetry of 188Re-hydroxyethylidene diphosphonate in human prostate cancer skeletal metastases

188Re-Hydroxyethylidene diphosphonate ((188)Re-HEDP) was used in previous studies for the palliative treatment of metastatic bone pain. However, the kinetic and radiation-absorbed doses have not been well documented. Therefore, the aim of this study was to gather dosimetric data for (188)Re-HEDP.

METHODS

Thirteen prostate cancer patients with skeletal involvement were treated with 2,700-3,459 MBq (mean dose, 3,120 MBq) (188)Re-HEDP. Patients underwent whole-body scans 3, 20, and 28 h after therapy. The effective half-life, residence time, and radiation-absorbed dose values were calculated for the whole body, bone marrow, kidneys, and bladder as well as for 29 bone metastases. The urinary excretion rate was determined in 6 urine samples of each patient collected over 48 h at 8-h intervals beginning immediately after the administration of (188)Re-HEDP. After injection of (188)Re-HEDP, blood samples were taken weekly for 6 wk, and platelet and leukocyte counts were performed.

RESULTS

The mean effective half-life was 15.9 +/- 3.5 h in bone metastases, 10.9 +/- 2.1 h in the bone marrow, 11.6 +/- 2.1 h in the whole body, 12.7 +/- 2.2 h in the kidneys, and 7.7 +/- 3.4 h in the bladder. The following radiation-absorbed doses were calculated: 3.83 +/- 2.01 mGy/MBq for bone metastases, 0.61 +/- 0.21 mGy/MBq for the bone marrow, 0.07 +/- 0.02 mGy/MBq for the whole body, 0.71 +/- 0.22 mGy/MBq for the kidneys, and 0.99 +/- 0.18 mGy/MBq for the bladder. (188)Re-HEDP showed a rapid urinary excretion within the first 8 h after therapy, with 41% of the (188)Re-HEDP administered being excreted. Forty-eight hours after therapy, the excretion rate was 60% +/- 12%. Only 1 patient showed a decrease of platelet count below 100 x 10(9) counts/L. None of the patients presented with a decrease of leukocyte count below 3.0 x 10(9) counts/L.

CONCLUSION

(188)Re-HEDP is an effective radiopharmaceutical used in the palliative treatment of metastatic bone pain. The radiation-absorbed dose is acceptable for bone pain palliation with low doses for the normal bone marrow and the whole body.

Risedronate Once A Week

Risedronate (risedronic acid), an orally administered pyridinyl bisphosphonate, inhibits osteoclast-mediated resorption of bone and modulates bone metabolism in women with postmenopausal osteoporosis. The long terminal exponential half-life of risedronate (480 hours) has led to the development of a 35mg tablet for once-a-week administration. The beneficial effects of risedronate 35mg once a week on total hip, femoral neck and trochanter bone mineral density (BMD) at 12 months were similar to those of risedronate 5mg once daily. Risedronate 35mg once a week was as effective as risedronate 5mg once daily in improving lumbar spine BMD in a randomized, double-blind, multicenter trial of 1456 women with postmenopausal osteoporosis. Mean percentage increases in BMD from baseline at 12 months were 3.94% and 4.25% in the 35mg and 50mg once-a-week dose groups, compared with 4% in the 5mg once-daily dose group. The differences between the once-a-week doses and the once-daily dose met the predetermined criterion for non-inferiority. An historical analysis suggested that risedronate 35mg once a week reduced the incidence of vertebral fracture significantly more than placebo. The tolerability profile (including the incidence of upper gastrointestinal adverse events) of risedronate 35mg once a week in women with postmenopausal osteoporosis, was similar to that of risedronate 5mg once daily.

Bisphosphonates inhibit angiogenesis in vitro and testosterone-stimulated vascular regrowth in the ventral prostate in castrated rats

Bisphosphonates (BPs) are used currently in the treatment of patients with bone metastases because these compounds inhibit bone resorption. We examined here the effects of BPs on inhibition of endothelial cell functions in vitro and in vivo. Treatment of endothelial cells with BPs (clodronate, risedronate, ibandronate, and zoledronic acid) reduced proliferation, induced apoptosis, and decreased capillary-like tube formation in vitro. Quantification of blood vessels in bone biopsy specimens from patients with Paget's disease before and after clodronate treatment showed a 40% reduction of the vascularization after BP treatment. However, such a decreased vascularity could be secondary to a reduction of bone resorption. Therefore, the tissue distribution of [14C]BPs in male rats was examined to develop an angiogenesis model in a noncalcified tissue where BPs could accumulate. [14C]BPs (zoledronic acid, ibandronate, and clodronate) not only accumulated in bone but also transiently accumulated in the prostate. The effects of BPs on testosterone-induced revascularization of the prostate gland in castrated rats were then studied. Testosterone in combination with ibandronate or zoledronic acid induced a 17-35% reduction of the prostate weight compared with castrated rats treated with testosterone alone. Blood vessel immunostaining on prostate tissue sections revealed that both ibandronate and zoledronic acid induced a 50% reduction of the revascularization of the prostate gland. Moreover, zoledronic acid did not alter testosterone-induced activity of a luciferase gene reporter construct transfected in androgen-dependent prostatic cells, indicating that this BP did not directly interfere with testosterone. In conclusion, BPs have in vivo antiangiogenic properties, which could be of relevance to improve therapy and prevention of bone metastasis. In addition, our results extend the potential clinical use of BPs to patients with early prostate cancer.

Review of risedronate in the treatment of osteoporosis

Risedronate (Actonel, Procter & Gamble and Aventis) is a novel, orally administered pyridinyl bisphosphonate. Preclinical studies have shown that risedronate is a potent inhibitor of osteoclasts. Risedronate inhibited bone resorption and increased bone density in the spine and hip. Prospective, randomised, placebo-controlled trials (RCTs) in patients with postmenopausal osteoporosis (PMO) have demonstrated that risedronate decreased the risk of vertebral fractures by up to 49% and of non-vertebral fractures by up to 39% over 3 years in postmenopausal women with one or more prevalent vertebral fractures. This reduction of the risk for vertebral fractures was significant from the first year of treatment (risk reduction up to 65%). Risedronate was the first bisphosphonate to be studied in a large RCT with prevention of hip fracture as the primary end point. In this study, risedronate reduced the risk of hip fracture by 40% in elderly women with low hip bone density and one clinical risk factor for hip fracture and by 60% in women with low bone density and a prevalent vertebral fracture at baseline. Risedronate was also effective in the prevention and treatment of bone loss in glucocorticoid-induced osteoporosis (GIO), with a positive effect on vertebral fractures within the first year. Risedronate was well-tolerated with a safety profile comparable to placebo in all clinical studies. Patients with a previous or current history of upper GI illness or who were taking NSAIDs or aspirin were not excluded from these studies. Importantly, the upper GI safety profile of risedronate was shown to be similar to that of placebo in endoscopic studies. There was no evidence of acute-phase reactions or primary mineralisation defects. The most appropriate dose of risedronate was 5 mg/day.

186Re-1,4,8,11-tetraaza cyclotetradecyl-1,4,8,11-tetramethylene phosphonic acid: a novel agent for possible use in metastatic bone-pain palliation

In connection with our work on the development of 186Re-tetra-phosphonates with optimum properties for use in bone pain palliation, a novel cyclic tetraphosphonate derivative, has been synthesized, complexed with 186Re and evaluated with promising results. The ligand, which consists of a cyclic array of tetra-aminomethylphosphonate groups, was synthesized using orthophosphorus acid, 1,4,8,11-tetraazacyclotetradecane and formaldehyde. The labeling conditions with 186Re have been standardized under varying reaction conditions to give maximum yield. In a reaction volume of 1 mL, maximum complexation yield of 98% was observed at pH 2 using 0.1 mg Re (37-370 MBq) for a ligand concentration at 9 x 10(-2) M/L, under heating at 100 degrees C for 30 min with 2 mg of stannous chloride. The complex was found to be stable for 6 days with RC purity remaining approximately 97%. The complex was characterized by paper chromatography in saline and acetone, wherein the R(f) exhibited were 0.9 and 0, respectively. Biodistribution studies of the complex were performed in male Wistar rats. Activity in femur which was observed to be 1.8%/g (equivalent to about 23% of the injected activity in skeleton) at 3 h post injection remained almost constant up to 48 h. Minimum activity was observed in blood and other soft tissues. The complex showed major renal clearance. Scintigraphic images in rabbits after injecting 70-100 MBq of 186Re-CTMP and using a dual head gamma camera were observed to be superior to 186Re-HEDP, prepared by a procedure standardized by us. Insignificant activity was observed in other vital organs. The results suggest the suitability of the complex for further evaluation in higher animals for bone pain palliation.

Risedronate pharmacokinetics and intra- and inter-subject variability upon single-dose intravenous and oral administration

PURPOSE

To determine the pharmacokinetics and absolute bioavailability of risedronate after single-dose oral administration of 30 mg risedronate as a tablet and an aqueous solution, and 0.3 mg risedronate as an intravenous infusion.

METHODS

This study was a randomized, three-treatment, four-period, partial replicate crossover study involving 33 healthy volunteers. Treatments were administered 7 weeks apart, and the third treatment was repeated during the fourth period. Serum and urine were collected over 72 hours and 672 hours, respectively.

RESULTS

Following intravenous administration, renal clearance accounted for 87% of total clearance, with 65% of the dose excreted within 24 hours and 85% of the dose excreted within four weeks. The absolute bioavailability was approximately 0.62% after both oral formulations, and the relative bioavailability of the tablet compared with the oral solution was 104%. The rate and extent of absorption from the two formulations were bioequivalent based on the range proposed for highly variable drugs. Intrasubject variability following oral administration was 50-80%, and was primarily associated with absorption.

CONCLUSION

The majority of the total clearance after intravenous administration of risedronate was renal clearance, indicating that only a small percentage of a systemic dose is potentially incorporated, or "cleared," into bone. The absolute bioavailability of orally administered risedronate is approximately 0.6%, and is independent of formulation. Variability in the pharmacokinetics following oral administration is primarily associated with intrasubject variability in absorption.

Skeletal uptake and soft-tissue retention of 186Re-HEDP and 153Sm-EDTMP in patients with metastatic bone disease

The aim of this study was to introduce a new quantification method for 153Sm-ethylenediaminetetramethylenephosphonate (EDTMP) and 186Re-(tin)1,1-hydroxyethylidene diphosphonate (HEDP) to separately measure bone uptake and soft-tissue retention of these radiopharmaceuticals.

METHODS

Studies were performed on 23 men and 6 women undergoing radionuclide therapy for palliation of bone pain. Whole-body images were acquired at 3 min, 3-4 h, and 24-72 h after injection of 1,295 MBq 186Re-HEDP and 37 MBq 153Sm-EDTMP per kilogram of body weight. The activities for whole body, urinary bladder, and both thighs, as representative of soft tissue, were measured by region-of-interest technique. A background region of interest adjacent to the head was used to correct for bremsstrahlung. Bone uptake was calculated as initial whole-body activity minus urinary excretion and remaining soft-tissue activity.

RESULTS

For 186Re-HEDP (n = 11) the mean bone uptake at 3 h after injection was 13.7% +/- 8.6% of initial whole-body activity. The remaining soft-tissue activity was 49.4% +/- 16.9%, and urinary excretion was 36.9% +/- 14.4%. At 24 h after injection, bone uptake reached a value of 21.8% +/- 9.0%. Urinary excretion increased to 65.3% +/- 12.8% according to a decreasing soft-tissue remainder activity of 12.8% +/- 5.4%. The corresponding results for 153Sm-EDTMP (n = 18) at 3 h after injection were 29.2% +/- 15.5% for bone uptake, 32.3% +/- 12.9% for urinary excretion, and 38.4% +/- 14.5% for soft tissue. At 24 h after injection, we calculated values of 47.7% +/- 11.2% for bone uptake, 39.5% +/- 13.8% for urinary excretion, and 12.7% +/- 4.7% for soft tissue.

CONCLUSION

Bone uptake and soft-tissue retention for both 186Re-HEDP and 153Sm-EDTMP as obtained in this study agree well with the conventional 24-h whole-body retention measurements for these tracers. However, by this new scintigraphic quantification method, bone uptake and soft-tissue retention can be calculated separately, thus providing more detailed kinetic data and potentially improving the dosimetry of these radiopharmaceuticals in, for example, assessment of radiation dosage to bone and bone marrow.

Treatment of osteoporosis with bisphosphonates

Bisphosphonates are safe and effective agents for treatment and prevention of osteoporosis. Alendronate and risedronate are the best studied of all agents for osteoporosis in terms of efficacy and safety. They increase bone mass. In patients who have established osteoporosis, they reduce the risk of vertebral fractures. They are the only agents shown in prospective trials to reduce the risk of hip fractures and other nonvertebral fractures. They are approved by the US FDA for prevention of bone loss in recently menopausal women, for treatment of postmenopausal osteoporosis, and for management of glucocorticoid-induced bone loss. Other bisphosphonates (e.g., etidronate for oral use, pamidronate for intravenous infusion) are also available and can be used off-label for patients who cannot tolerate approved agents. Bisphosphonates combined with estrogen produce greater gains in bone mass compared with either agent used alone; whether there is a greater benefit of combination therapy on fracture risk is not clear. Combining a bisphosphonate with raloxifene or calcitonin is probably safe, although data on effectiveness are lacking.

Oesophageal transit, disintegration and gastric emptying of a film-coated risedronate placebo tablet in gastro-oesophageal reflux disease and normal control subjects

BACKGROUND

Risedronate sodium is a pyridinyl bisphosphonate, proven effective for the treatment and prevention of postmenopausal osteoporosis and glucocorticoid-induced osteoporosis and Paget's disease of the bone.

AIM

To compare the oesophageal transit, disintegration and gastric emptying of the commercial film-coated risedronate tablet in subjects with gastro-oesophageal reflux disease (GERD) and normal control subjects.

METHODS

A total of 30 subjects, 15 patients with GERD and 15 age- and sex-matched, normal control subjects, participated in a single-centre, open-label, comparative gamma scintigraphy study. The GERD subjects had active erosive oesophagitis within 4 weeks prior to dosing.

RESULTS

The mean oesophageal transit (GERD, 4.4 s; controls, 3.1 s), mean disintegration (GERD, 21.8 min; controls, 19.2 min) and mean gastric emptying (GERD, 15.9 min; controls, 15.0 min) were similar in the two subject groups. The oesophageal transit is rapid and given the rapid disintegration and gastric emptying, oesophageal contact occurring via reflux of risedronate was unlikely since most, if not all, of the dosage form exited from the stomach within 30 min.

CONCLUSIONS

The oval shape and film-coating on the commercial risedronate tablet promotes rapid oesophageal transit and minimizes oesophageal contact, even in the high-risk GERD population.

Risedronate

Risedronate is a novel orally administered pyridinyl bisphosphonate indicated for the prevention or treatment of postmenopausal and glucocorticoid-induced osteoporosis and Paget's disease. The drug reduces bone turnover and decreases resorption chiefly through osteoclastic effects, with no undesirable effects on cortical porosity or thickness or on cancellous bone volume. Four randomised, double-blind trials have been carried out in 4873 patients with postmenopausal osteoporosis. In 2 of these studies, the primary end-point of vertebral fracture incidence was reduced by risedronate 5mg once daily by up to 65 and 49% relative to placebo after 1 and 3 years, respectively. Across all 4 trials, risedronate improved lumbar spine, femoral neck and femoral trochanter bone mineral density (BMD) statistically significantly relative to placebo. The drug also prevented bone loss in a study in 383 women with recent menopause, and reduced the risk of hip fracture in elderly women with confirmed osteoporosis in a trial involving a total of 9331 patients. Risedronate 5 mg/day plus estrogen has been shown to be superior to estrogen alone in a 12-month double-blind study in 524 women with at least 1-year's history of menopause. Two randomised, double-blind and placebo-controlled 12-month studies in a total of 518 patients have shown risedronate 5 mg/day to prevent or reverse bone loss in patients receiving glucocorticoid therapy. Risedronate 30 mg/day was associated with statistically significant reductions in mean serum levels of alkaline phosphatase (ALP) in noncomparative studies in patients with Paget's disease. ALP normalisation rates ranged from 53.8 to 65% across two 84-day treatment cycles in 2 of these trials in 180 patients. In a randomised, double-blind study in 123 patients, risedronate 30 mg/day for 2 months evoked significantly greater serum ALP responses than etidronate 400 mg/day for 6 months. The overall tolerability profile of risedronate was similar to that of placebo in clinical studies, with no evidence of acute-phase reactions or mineralisation defects, or excess incidence of upper GI lesions, in patients receiving the drug.

CONCLUSIONS

Risedronate is an effective and well tolerated novel bisphosphonate that is suitable for first-line therapy in Paget's disease. The rapid and sustained reductions in vertebral fracture incidence and BMD changes seen in patients with postmenopausal and glucocorticoid-induced osteoporosis indicate the drug to be a valuable treatment option with first-line potential, particularly in patients for whom hormonal therapy is inappropriate. The effects of the drug on hip fracture incidence in elderly women with confirmed osteoporosis point to a particular role in older patients, or those with more advanced disease.

Bisphosphonate prodrugs: synthesis and in vitro evaluation of alkyl and acyloxymethyl esters of etidronic acid as bioreversible prodrugs of etidronate

The synthesis and preliminary evaluation of novel alkyl and acyloxymethyl esters of etidronic acid as etidronate prodrugs is reported. Tetramethyl ester of etidronic acid was found be isomerized at pH 7.4 and P-C-P bridge was rearranged to P-C-O-P. This unwanted process was prevented via acylation of the bridging carbon's alcohol group. Acylation showed to be stable if one or more phosphonic OH- groups were substituted. However, when none of the phosphonic OH- groups were substituted, the acylation was chemically hydrolysed and the parent drug was released. This finding was successfully applied in the design of tetrapivaloyloxymethyl ester of acetylated etidronic acid which released etidronic acid via enzymatic (first step) and chemical (second step) hydrolysis in liver homogenate. However, the corresponding tri-substituted pivaloyloxymethyl ester having adequate water-solubility and lipophilicity (logP(app) 0.6 at pH 7.4), is probably the most potential prodrug candidate reported to enhance the oral bioavailability of etidronate.

The time of day that etidronate is ingested does not influence its therapeutic effect in osteoporosis

To investigate whether the therapeutic effect of etidronate is affected by the time of ingestion we have retrospectively studied 110 osteoporotic patients. They had been taking etidronate according to the manufacturer's instructions for a mean duration of 2.6 years either on waking (n=47), on retiring (n=47), or during the day (n= 16). No significant differences were found between the three groups with respect to percentage change in bone mineral density at all sites either for the first year of treatment or for the mean yearly percent change throughout the total course of treatment. These findings suggest that the time of ingestion of etidronate does not influence the therapeutic effect if a two hour fast before and after ingestion is adhered to.

Effect of renal function on risedronate pharmacokinetics after a single oral dose

AIMS

To determine the relationship between risedronate pharmacokinetics and renal function.

METHODS

Risedronate was administered to adult men and women (n=21) with various degrees of renal function (creatinine clearance 15-126 ml min-1 ) as a single oral dose of 30 mg. Serum samples were obtained for 72 h after dosing, and urine samples were collected for 72 h after dosing and then periodically for 6 weeks. Risedronate concentrations were determined using an enzyme-linked immunosorbent assay (ELISA). Risedronate serum concentration-time and urinary excretion rate-time profiles were analysed simultaneously using nonlinear regression.

RESULTS

Renal clearance and volume of distribution were linearly related to creatinine clearance (r2=0.854, P<0.001; and r2=0.317, P<0.01, respectively). Decreases in predicted renal clearance and volume of distribution of 82 and 69%, respectively, were observed when creatinine clearance decreased from 120 to 20 ml min-1. A 64% decrease in predicted oral clearance was observed when creatinine clearance decreased from 120 to 20 ml min-1 (P=0.064). Iohexol clearance, a predictor of renal function, produced similar results to those observed with creatinine clearance. Risedronate was well tolerated by the study population.

CONCLUSIONS

Risedronate renal clearance was significantly related to a decrease in renal function. There was a consistent reduction in oral clearance with a decrease in creatinine clearance. However, based on the regression analysis, generally no dosage adjustment appears to be necessary for most patients with mild or moderate renal impairment (creatinine clearance >20 ml min-1 ).

Dose-proportional pharmacokinetics of risedronate on single-dose oral administration to healthy volunteers

Risedronate is a pyridinyl bisphosphonate approved for the treatment of Paget's disease (US-FDA) and in development for the treatment and prevention of osteoporosis. This study examined risedronate pharmacokinetics and tolerability after oral administration using a randomized, double-blind, parallel-group design. Healthy male and female volunteers (n = 22-23 subjects per dose) received a single oral dose of 2.5, 5, or 30 mg risedronate. Serum and urine samples were collected for 72 and 672 hours, respectively, and risedronate concentrations were determined by ELISA. Safety was evaluated by monitoring adverse events, clinical laboratory measurements, vital signs, and electrocardiograms. Mean Cmax (0.41, 0.94, and 5.1 ng/mL for 2.5, 5, and 30 mg, respectively), AUC (1.8, 3.9, and 21 ng.h/mL for 2.5, 5, and 30 mg, respectively), and urinary excretion (22, 63, and 260 micrograms for 2.5, 5, and 30 mg, respectively) were dose proportional, and there were no significant differences in tmax or CLR among the three doses. All doses were well tolerated; no serious adverse events occurred, and all but one of the adverse events were mild or moderate in severity. There was no evidence of an acute phase reaction occurring after oral administration of risedronate.

The effect of dosing regimen on the pharmacokinetics of risedronate

AIMS

To examine the effect of timing of a risedronate dose relative to food intake on the rate and extent of risedronate absorption following single-dose, oral administration to healthy male and female volunteers.

METHODS

A single-dose, randomized, parallel study design was conducted with volunteers assigned to four treatment groups (31 or 32 subjects per group, 127 subjects total). Each subject was orally administered 30 mg risedronate. Group 1 was fasted for 10 h prior to and 4 h after dosing (fasted group); Groups 2 and 3 were fasted for 10 h and were dosed 1 and 0.5 h, respectively, before a high-fat breakfast; and Group 4 was dosed 2 h after a standard dinner. Blood and urine samples were collected for 168 h after dosing. Pharmacokinetic parameters were estimated by simultaneous analysis of risedronate serum concentration and urinary excretion rate-time data.

RESULTS

Extent of risedronate absorption (AUC and Ae ) was comparable (P=0.4) in subjects dosed 2 h after dinner and 0.5 h before breakfast; however, a significantly greater extent of absorption occurred when risedronate was given 1 or 4 h prior to a meal (1.4- to 2.3-fold greater). Administration 0.5, 1, or 4 h prior to a meal resulted in a significantly greater rate of absorption (Cmax 2.8-, 3.5-, and 4.1-fold greater, respectively) when compared with 2 h after dinner.

CONCLUSIONS

The comparable extent of risedronate absorption when administered either 0.5-1 h before breakfast or 2 h after an evening meal support previous clinical studies where risedronate was found to have similar effectiveness using these dosing regimens. This flexibility in the timing of risedronate administration may provide patients an alternative means to achieve the desired efficacy while maintaining their normal daily routine.

Esophageal transit of risedronate cellulose-coated tablet and gelatin capsule formulations

Risedronate sodium is an orally active antiresorptive agent and a member of the pyridinyl class of bisphosphonates. It has been approved for the treatment of Paget's disease of the bone and is under development as a chronic therapy for the treatment and prevention of osteoporosis. A novel cellulose film-coated tablet formulation was developed to optimize esophageal transit of this bisphosphonate. The aim of the present study was to compare the esophageal transit of the film-coated tablet formulation of risedronate with its original gelatin capsule dose form. A total of 25 elderly, healthy volunteers (mean 66 years), who were dysphagia-free, participated in this randomized cross-over study. On separate occasions, volunteers swallowed radiolabeled placebo formulations with 50 ml water. Dynamic images with participants in a sitting position were recorded for 10 min using a gamma camera. Scintigraphic imaging showed a delay in esophageal transit (greater than 15 s) in 28% of patients in the capsule group but in none of the tablet group (P<0.05). The mean transit times of the capsules and tablets were 23.8 and 3.3 s, respectively. Esophageal transit of film-coated tablets was faster than gelatin capsules, suggesting that film-coated tablets would be the appropriate formulation for all pivotal trials with risedronate and for subsequent commercialization.

Effect of reaction conditions on preparations of rhenium-188 hydroxyethylidene diphosphonate complexes

Rhenium-186 (Re-186) hydroxyethylidene diphosphonate (HEDP) has been shown to localize in metastatic foci within bone in a manner similar to Tc-99m bone-seeking agents. Usually, in the preparation of diagnostic Tc-99m radiopharmaceuticals, the concentration of Tc is at trace level (10(-8) M). However, large amounts of carrier are included in the preparation of Re-186 radiopharmaceuticals (10(-4) M), which may significantly affect the preparation of Re-HEDP. In this study, Re-188 was used as an Re tracer. The effects of pH and concentrations of Re carrier on the preparation of Re-HEDP were investigated. Re-188-Sn-HEDP was prepared by reconstitution of a kit of lyophilized HEDP mixture, and tin chloride with a radioactive solution of perrhenate in saline. The total concentration of Re present in this work ranged from 10(-8) to 10(-3) M. The results showed that high labeling efficiency was obtained for each preparation. Although the chemical behaviors of the Re-188 HEDP complexes, with and without carrier, were similar, the biodistribution patterns of carrier free Re-188 HEDP in rats were found to differ from the biodistribution patterns of carrier-added Re-188 HEDP.

Etidronate and alendronate in the treatment of postmenopausal osteoporosis

OBJECTIVE

To review the clinical trials evaluating the efficacy of etidronate and alendronate in the treatment of established postmenopausal osteoporosis.

DATA SOURCE

A MEDLINE search was performed (from 1966 through September 1998) using the search terms bisphosphonates, etidronate, alendronate, and postmenopausal osteoporosis. English-language articles were considered for review.

STUDY SELECTION AND DATA EXTRACTION

Prospective, randomized, double-blind, placebo-controlled clinical trials using fracture as an end point were selected to review the efficacy of etidronate and alendronate in the treatment of postmenopausal osteoporosis. Results for the outcomes of bone mineral density (BMD) and fracture are summarized.

DATA SYNTHESIS

Etidronate and alendronate increase spinal BMD in postmenopausal women with osteoporosis. In one study, etidronate decreased the number of women sustaining new radiographic vertebral fractures over two years, but this effect was lost after three years of treatment. Alendronate reduces the number of radiographic vertebral fractures in postmenopausal women with a low bone mass. In women with preexisting fractures, alendronate decreases the number of patients with radiographic vertebral fractures, clinical (i.e., symptomatic vertebral and nonvertebral) fractures, and hip fractures. A significant reduction in the overall number of nonvertebral fractures has not been demonstrated in clinical trials evaluating either alendronate or etidronate.

CONCLUSIONS

No studies have directly compared the efficacy of alendronate and etidronate and the results of long-term clinical trials (i.e., >5 y) have not been published. Based on the results obtained in clinical trials using fracture as an end point, alendronate appears to be the bisphosphonate of choice. Safety profiles and cost should also be considered in the choice of etidronate or alendronate for the treatment of postmenopausal osteoporosis.

Pharmacokinetics of bisphosphonates in rabbits

Clodronate, pamidronate and etidronate are commonly used bisphosphonates, which accumulate extensively in arteries and some other tissues. We compared their pharmacokinetics in rabbits with those of tiludronate, the drug newly introduced to clinical use. The 14C-labelled drugs were given intravenously and plasma drug levels were monitored for up to 24 hr. The dose-related plasma concentrations of tiludronate and etidronate were clearly higher and decreased more slowly than those of clodronate and pamidronate (P < 0.001). Already at 5 min., the concentrations of tiludronate and etidronate were higher than those of clodronate and pamidronate (P = 0.016). At 24 hr, plasma concentration of tiludronate was 12 +/- 6.6%, of etidronate 18 +/- 2.5%, of clodronate 0.8 +/- 0.2%, and of pamidronate 1.4 +/- 0.4% of the dose per body weight. With the same dose (25 mg/kg), absolute AUC0-24 hr for tiludronate and etidronate was 9-11 times larger than for clodronate. AUC0-24 hr for pamidronate (2.5 mg/kg) was 11% of that for clodronate. Plasma clearance of tiludronate and etidronate was 9-15 times slower than that of clodronate and pamidronate. At 24 hr, the mean tissue-to-plasma ratio of tiludronate for aorta was 1.2-1.6. For bone, spleen, liver and kidneys the ratio varied from 5.4 to 52.6. The results suggest that 1) tiludronate and etidronate are removed from plasma much slower than clodronate and pamidronate, and 2) the potential of tiludronate to concentrate in arteries and bone is generally smaller than previously found with the other bisphosphonates.

Risedronate

Risedronate is a pyridinyl bisphosphonate that can be administered orally in lower dosages than other antiresorptive bisphosphonates. Like others of its class risedronate inhibits osteoclast-mediated bone resorption. In experimental models of osteoporosis, risedronate inhibited bone loss and improved trabecular architecture. In patients with Paget's disease, pain diminished or disappeared and serum alkaline phosphatase levels decreased after treatment with oral risedronate 30 mg/day for < or = 3 months. Risedronate 30 mg/day orally for 2 months significantly reduced pain, whereas etidronate 400 mg/day orally for 6 months tended to reduce pain, in a randomised double-blind trial of patients with Paget's disease. Oral risedronate 5 mg/day for < or = 2 years increased bone mass in postmenopausal women with low or normal bone mass. Risedronate 2.5 mg/day prevented bone loss in postmenopausal women treated with glucocorticoids for rheumatoid arthritis. The incidence of gastrointestinal or other adverse events was similar in patients treated with risedronate or placebo in clinical trials.

Transformation of bisphosphonates into insoluble material in human blood in vitro

The aim of the study was to find out whether bisphosphonates transform into insoluble material in human blood and serum in vitro. Samples of fresh blood and serum were incubated with various concentrations of 14C-labelled clodronate, etidronate, pamidronate and tiludronate for 2 h and 8 h at 37 degrees C. The presence of unfiltrable material in the plasma separated from the blood, and in the serum were studied with 1) 100, 300 and 1,000 kd (kilo Daltons) filter tubes centrifuged at 3,000 g for 60 min, and 2) high-speed centrifugation at 13,000 g for 30 min. The radioactivities in the ultrafiltrates and supernatants were compared to those in the native plasma or serum. All bisphosphonates transformed into unfiltrable material, which was separated from the samples with the 100 and 300 kd filters but not with the 1,000 kd filter. The material was not sedimented with the high-speed centrifugation. The lengthening of the incubation time from 2 h to 8 h increased the unfiltrable fraction, which generally was dependent on the drug concentration in the blood, too. However, the fraction of the unfiltrable material did not seem to increase with time when the drug was incubated with serum instead of blood. Since drug binding to plasma proteins is generally a very rapid process, some factors other than proteins only, e.g. cations or cation residues, present in the blood but not in the serum, should be involved in transforming of bisphosphonates into insoluble material in the blood.

Rhenium-188(Sn)HEDP for treatment of osseous metastases

Rhenium-188 (tin) hydroxyethylidine diphosphonate [188Re(Sn)HEDP] is a new radiopharmaceutical that localizes in skeletal metastases and emits beta particles that may be therapeutically beneficial.

METHODS

It was evaluated by in vitro and in vivo testing in the laboratory, in animals and in humans using 188Re from a variety of sources. It may be produced by a desk-top method developed previously for 186Re(Sn)HEDP using 188Re produced through neutron irradiation of either enriched 187Re or naturally occurring rhenium targets or the use of a 188W/188Re generator.

RESULTS

So long as the mass of rhenium in the 188Re-perrhenate to be processed into 188Re(Sn)HEDP is at least 100 microg, satisfactory radiochemical yields and purity may be obtained by all methods. The 188Re(Sn)HEDP has biodistribution and radiation dosimetry characteristics that are similar to those noted previously for 186Re(Sn)HEDP and appears to result in similar benefits and toxicities in patients with skeletal metastases. External radiation exposure monitoring indicates that, only 4 hr after a therapeutic administration of 1110 MBq (30 mCi) of 188Re(Sn)HEDP, average exposure rates at 1 meter from the patient would be only 0.5 mR/hr.

CONCLUSION

Same-day, on-demand, outpatient therapy of disseminated skeletal metastases appears to be feasible with 188Re(Sn)HEDP.

Risedronate gastrointestinal absorption is independent of site and rate of administration

PURPOSE

Two studies were conducted to compare the absorption of risedronate administered as a solution to three different gastrointestinal sites (study A) and to determine the extent of absorption of risedronate solution administered by rapid and slow infusion to the second part of the duodenum (study B).

METHODS

Each study was designed as a single-dose, crossover (three periods, study A; two periods, study B) trial in healthy male subjects, with a 14-day washout period between dosing. Subjects fasted overnight before drug administration and for 4 hours after drug administration. In study A, a risedronate solution of 40 mg in 30 mL of water was administered directly into the stomach, the second part of the duodenum, or the terminal ileum over 1 minute via a nasoenteral tube in a three-period crossover design. In study B, a risedronate solution of 40 mg in 30 mL of water was administered directly into the second part of the duodenum over 1 minute and over 1 hour in a randomized, two-period crossover design. Serum and urine samples were obtained for 48 hours after dosing for risedronate analysis.

RESULTS

Eight subjects completed each study. No statistically significant site-specific differences in any pharmacokinetic parameter were observed (study A). Based on the area under the serum concentration-time profile and the amount of drug excreted in the urine unchanged, the extent of risedronate absorption did not differ significantly following a rapid or a slow infusion (study B). Only minor symptomatic complaints were reported by subjects, such as headaches and body aches.

CONCLUSIONS

These studies indicate that the rate and extent of risedronate absorption are independent of the site of administration along the gastrointestinal tract, and that the extent of absorption is not affected by the rate of administration.

Rhenium-188 hydroxyethylidene diphosphonate: a new generator-produced radiotherapeutic drug of potential value for the treatment of bone metastases

The search for an ideal radioisotope for systemic radiotherapy continues. As a generator-produced radioisotope emitting both beta and gamma rays and having a short physical half-life of 16.9 h, rhenium-188 is a very good potential candidate for systemic radiotherapy. In this study, we labeled hydroxyethylidene diphosphonate (HEDP) with 188Re and analyzed the biodistribution and bone uptake following intravenous injection in rats to assess its potential for clinical use. The rats were injected with approximately 14.8 MBq (0.4 mCi) 188Re-HEDP in a volume of 0.1 ml intravenously and then sacrificed at 1 h, 24 h, or 48 h (four rats at each time). Samples (about 0.1 g) of lung, liver, kidney, spleen, testis, muscle, stool, and bone (thoracic vertebra) were taken and weighed carefully. In addition, a 1-ml sample of blood was drawn from the heart and 1 ml of urine was taken from the urinary bladder immediately after killing. Tissue concentrations were calculated and expressed as percent injected dose per gram or per milliliter (% ID/g or ml). Bone lesions were created in the right tibial bone in three rabbits to calculate the lesion to normal uptake ratio (L/N ratio). The biodistribution data showed that the radioactivity in the bone tissue was as high as 1.877% ID/g at 1 h and that it climbed to 2.017% ID/g at 4 h. The activity level in the kidney was highest at 1 h but declined rapidly throughout the study. The radioactivities in the lung, liver, muscle, spleen, testis, blood, and stool were all lower than 0.3% ID/g at 1 h and also declined rapidly. The biological half-life in bone was the longest (60.86 h). In contrast, the biological half-lives in muscle and blood were short (2.99 h and 6.21 h respectively). The concentrations of radioactivity in muscle, spleen, testis, and stool were quite low throughout the study. Most of the radiotracer was excreted by the urinary system. The L/N ratio was 4.23+/-0.21 in rabbits injected with 188Re-HEDP and 4.25+/-0.23 in those injected with technetium-99m methylene diphosphonate. In conclusion, we would suggest that 188Re-HEDP is a very good potential candidate for the treatment of bone metastases because of the following characteristics: (1) it is generator produced; (2) it has a short half-life; (3) it emits gamma rays suitable for imaging; (4) there is highly selective uptake in the skeletal system and bone lesions; and (5) it has a low non-target uptake and rapid clearance in nonosseous tissue.

Gastric uptake during Re-186 HEDP bone scintigraphy

In bone scintigraphy extraosseous uptake of the radiopharmaceutical (TcO4-, pertechnetate) is a common finding when the stomach is abnormally observed; this may be due to the instability of the radiopharmaceutical leading to free pertechnetate within this organ. The same explanation might be inculpate rhenium 186-HEDP, due to its similarity to Tc-99m MDP's sphysicochemical properties and behavior, as both radioisotopes are Group VII metals /1/ and are labelling the same ligand (a diphosphonate moiety). We report on 186Re-HEDP uptake in the stomach in two patients with osseous metastases because of prostate and breast cancer respectively out of a series of 52 cancer affected individuals, treated with 186Re-HEDP. The thorough clinical and laboratory investigation of both patients assessed that this extraosseous radio-rhenium accumulation was multifactorial with the main cause being a disturbance of body fluid acid-balance, favoring calcium and phosphate ion precipitation and leading to 186Re-HEDP extraosseous uptake.

Radionuclide therapy for prostate cancer lumbar metastasis prolongs symptom-free survival in a rat model

OBJECTIVES

The present study was initiated to explore the effects of hydroxyethylidene diphosphonate labeled with rhenium 186(186Re-HEDP) treatment on the progression of lumbar skeletal metastasis in an animal model and to correlate the eventual treatment efficacy with the radioisotope tissue distribution.

METHODS

The effect of 186Re-HEDP on the progression of lumbar metastasis from prostate cancer was investigated in the Copenhagen rat model. Metastatic prostate tumor deposits were induced in male rats by tail vein injection of R3327-MATLyLu prostate tumor cells under concomitant clamping of the inferior caval vein. The development of clinical symptoms such as onset of hind leg paralysis and urinary bladder swelling was monitored and related to the presence of tumor cells within histologic sections of L-5 and L-6 vertebrae.

RESULTS

The 186Re-HEDP administration, given either 1 day or 8 days after surgical induction of lumbar metastasis, could significantly increase the symptom-free survival of the animals. These results were confirmed by a significant decrease in the presence of histologically detectable tumor tissue. Biodistribution studies demonstrated the uptake of the major part of the radioisotope within bone tissue. Uptake of radioactivity within the lumbar vertebrae on a microscopic scale, as shown by phosphor screen autoradiography, was concentrated in areas of bone formation and turnover. Signs of radiotoxicity, such as bone marrow replacement by fat cells and the absence of megakaryocytes, were observed.

CONCLUSIONS

The results show that radionuclide treatment using 186Re-HEDP is a potentially efficacious treatment option in prostate cancer disseminated to the skeleton. The optimal treatment dose should be determined carefully and aimed at acceptable levels of myelotoxicity.

Treatment of metastatic bone pain using the bone seeking radiopharmaceutical Re-186-HEDP

Recent advances in radionuclide therapy offer a new approach for the management of metastatic bone pain. This paper reports the results of dosage escalation studies with 186Re-HEDP as a bone-seeking radiopharmaceutical in patients with bone metastases originating from breast or prostate cancer with regard to toxicity, pharmacokinetics and bone marrow dosimetry and the palliating effect on bone pain. Thrombocytopenia proved to be the dose limiting factor and 186Re-HEDP showed a considerable efficacy in end-stage patients with metastatic bone pain.