Safety, pharmacokinetics, and changes in bone metabolism associated with zoledronic acid treatment in Japanese patients with primary osteoporosis

Although once-yearly intravenous administration of zoledronic acid has been reported to inhibit bone resorption and increase bone mineral density, no studies have evaluated its effectiveness in treating osteoporosis in Japanese patients. Therefore, the purpose of this study was to investigate the pharmacokinetics and assess the safety of and changes in bone metabolism associated with zoledronic acid treatment in Japanese patients with primary osteoporosis. This was a single-administration study with a single-blind parallel-group design. The study participants were 24 Japanese patients with primary osteoporosis. The patients were divided into two groups, with each group receiving a single injection of zoledronic acid (4 or 5 mg). Pharmacokinetics and urinary excretion were then compared, and drug-related adverse events and changes in the levels of bone turnover markers were assessed at 12 months. Mean plasma concentrations of zoledronic acid peaked in both groups immediately after administration, and decreased to 1% or less of peak levels after 24 h. Noncompartmental analysis revealed that C _max and the area under the curve from time zero to infinity increased in proportion to the dose. The levels of bone resorption and formation markers decreased from day 15 and from 3 months after administration respectively, and suppression of these markers remained constant for the entire study period. No serious adverse events were reported. There was no large difference between the 4- and 5-mg groups in terms of pharmacokinetics, changes in the levels of bone turnover markers, and safety profiles. This study demonstrated acceptable pharmacokinetics and changes in bone metabolism associated with zoledronic acid treatment in female Japanese osteoporosis patients. Both the 4-mg dose and the 5-mg dose demonstrated acceptable safety and sustained antiresorptive effects for the duration of the study.

Utilizing time-lapse micro-CT-correlated bisphosphonate binding kinetics and soft tissue-derived input functions to differentiate site-specific changes in bone metabolism in vivo

The turnover of bone is a tightly regulated process between bone formation and resorption to ensure skeletal homeostasis. This process differs between bone types, with trabecular bone often associated with higher turnover than cortical bone. Analyses of bone by micro-computed tomography (micro-CT) reveal changes in structure and mineral content, but are limited in the study of metabolic activity at a single time point, while analyses of serum markers can reveal changes in bone metabolism, but cannot delineate the origin of any aberrant findings. To obtain a site-specific assessment of bone metabolic status, bisphosphonate binding kinetics were utilized. Using a fluorescently-labeled bisphosphonate, we show that early binding kinetics monitored in vivo using fluorescent molecular tomography (FMT) can monitor changes in bone metabolism in response to bone loss, stimulated by ovariectomy (OVX), or bone gain, resulting from treatment with the anabolic bone agent parathyroid hormone (PTH), and is capable of distinguishing different, metabolically distinct skeletal sites. Using time-lapse micro-CT, longitudinal bone turnover was quantified. The spine showed a significantly greater percent resorbing volume and surface in response to OVX, while mice treated with PTH showed significantly greater resorbing volume per bone surface in the spine and significantly greater forming surfaces in the knee. Correlation studies between binding kinetics and micro-CT suggest that forming surfaces, as assessed by time-lapse micro-CT, are preferentially reflected in the rate constant values while forming and resorbing bone volumes primarily affect plateau values. Additionally, we developed a blood pool correction method which now allows for quantitative multi-compartment analyses to be conducted using FMT. These results further expand our understanding of bisphosphonate binding and the use of bisphosphonate binding kinetics as a tool to monitor site-specific changes in bone metabolism in vivo.

How to approach hypercalcaemia

The management of patients with hypercalcaemia should be informed by the patient's symptoms and signs, by the degree of elevation of calcium, by the underlying mechanism by which calcium has been elevated and by the disease process underlying the presentation. Regardless of diagnosis, all significantly hypercalcaemic patients should be rendered euvolaemic before any further and more specific treatment is considered. Highly symptomatic patients and those with a calcium level of > 3.5 mmol represent a medical emergency that requires inpatient treatment.

Low bone density is not always bisphosphonate deficiency

Low bone density is not a one-size-fits-all disorder. We need to carefully consider the diagnostic and therapeutic options before assuming that low bone density is osteoporosis.

Bone density and bone turnover markers in patients with epilepsy on chronic antiepileptic drug therapy

In this comparative, cross-sectional study, we evaluated 55 patients with epilepsy on chronic use of antiepileptic drugs (AED); [(38 females and 17 males, 35 ± 6 years (25 to 47)] and compared to 24 healthy subjects (17 females/7 males). Laboratorial evaluation of bone and mineral metabolism including measurements of bone specific alkaline phosphatase (BALP) and carboxyterminal telopeptide of type I collagen (CTX-I) were performed. Bone mineral density (BMD) was measured by DXA. BALP and CTX-I levels did not differ significantly between the groups. CTX-I levels were significantly higher in patients who were exposed to phenobarbital (P< 0.01) than those who were not. Patients presented BMD of both sites significantly lower than the controls (0.975 ± 0.13 vs. 1.058 ± 0.1 g/cm²; p= 0.03; 0.930 ± 0.1 vs. 0.988 ± 0.12 g/cm²; p= 0.02, respectively). Total hip BMD (0.890 ± 0.10 vs. 0.970 ± 0.08 g/cm²; p< 0.003) and femoral neck (0.830 ± 0.09 vs. 0.890 ± 0.09 g/cm²; p< 0.03) were significantly lower in patients who had been exposed to phenobarbital, in comparison to the non-phenobarbital users. In conclusion, patients on AED demonstrate reduced BMD. Among the AED, phenobarbital seems to be the main mediator of low BMD and increases in CTX-I.

A new bisphosphonate-containing 99mTc(I) tricarbonyl complex potentially useful as bone-seeking agent: synthesis and biological evaluation

Aiming to develop new bone-seeking radiotracers based on the organometallic core fac-[(99m)Tc(CO)(3)](+) with improved radiochemical and biological properties, we have prepared new conjugates with phosphonate pendant groups. The conjugates comprise a chelating unit for metal coordination, which corresponds to a pyrazolyl-containing backbone (pz) with a N,N,N donor-atom set, and a pendant diethyl phosphonate (pz-MPOEt), phosphonic acid (pz-MPOH) or a bisphosphonic acid (pz-BPOH) group for bone targeting. Reactions of the conjugates with the precursor [(99m)Tc(H(2)O)(3)(CO)(3)](+) yielded (mote than 95%) the single and well-defined radioactive species [(99m)Tc(CO)(3)(kappa(3)-pz-MPOEt)](+) (1a), [(99m)Tc(CO)(3)(kappa(3)-pz-MPOH](+) (2a) and [(99m)Tc(CO)(3)(kappa(3)-pz-BPOH)](+) (3a), which were characterized by reversed-phase high-performance liquid chromatography . The corresponding Re surrogates (1-3), characterized by the usual analytical techniques, including X-ray diffraction analysis in the case of 1, allowed for macroscopic identification of the radioactive conjugates. These radioactive complexes revealed high stability both in vitro (phosphate-buffered saline solution and human plasma) and in vivo, without any measurable decomposition. Biodistribution studies of the complexes in mice indicated a fast rate of blood clearance and high rate of total radioactivity excretion, occurring primarily through the renal-urinary pathway in the case of complex 3a. Despite presenting moderate bone uptake (3.04 +/- 0.47% injected dose per gram of organ, 4 h after injection), the high stability presented by 3a and its adequate in vivo pharmacokinetics encourages the search for new ligands with the same chelating unit and different bisphosphonic acid pendant arms.

Analytical methods for the quantification of ibandronate in body fluids and bone

The accurate determination of bisphosphonate levels in bone and biological fluids is important in both clinical and pharmacological/toxicological studies. Ibandronate is a potent nitrogen-containing bisphosphonate containing a tertiary amine group, which does not easily form chromophore derivatives that can be detected by UV light or fluorescence emissions. The current report describes the methodology and validation of a GC-MS assay for ibandronate in serum/plasma and urine, a similar, modified GC-MS method for measurement of bone ibandronate levels, and an ELISA for ibandronate determination in serum/plasma. The range of quantification for the GC-MS was 1-100 ng/ml and 2-7500 ng/ml in plasma or serum and urine, respectively, and 50-1600 pg/ml (potentially 10-320 pg/ml depending on sample size) for the ELISA in plasma or serum. These assays were comparable. The practical application of the assays in preclinical and clinical studies is briefly reviewed.

Comparison of the predicted in vivo behaviour of the Sn(II)–APDDMP complex and the results as studied in a rodent model

In a quest for more effective radiopharmaceuticals for pain palliation of metastatic bone cancer, this paper relates results obtained with ((117m)Sn labelled) Sn(II) complexed to the bone seeking bisphosphonate, N,N-dimethylenephosphonate-1-hydroxy-3-aminopropylidenediphosphonate (APDDMP). APDDMP is synthesised from the known bone cancer pain palliation agent 1-hydroxy-3-aminopropylidenediphosphonate (APD, Pamindronate). This work is performed to utilise the idea that the low bone marrow radio toxicity of (117m)Sn could afford a highly effective radiopharmaceutical in pain palliation but also in the curative treatment of bone metastasis. Complex-formation constants of APDDMP with the important blood plasma metal-ions, Ca(2+), Mg(2+), Zn(2+) as well as the added metal ion, Sn(2+) were measured by glass electrode potentiometry at 25 degrees C and I = 150 mM. Blood plasma models were constructed using the computer code ECCLES and the results compared with those gathered from tests on a rodent model. The ((117m)Sn-labelled) Sn(II)-APDDMP complex was found to have only some liver and bone uptake although a high trabecular to normal bone ratio was recorded. From the blood plasma model this was shown to be primarily due to the high affinity of APDDMP for Ca(II) causing some of the Sn(II)-APDDMP complex to dissociate. High kidney uptake and excretion as well as high bladder uptake was recorded which was shown to be due to the dissociation of the Sn(II)-APDDMP complex in blood plasma. Animal model observations could be explained by the blood plasma modelling.

Determination of pamidronate in human whole blood and urine by reversed-phase HPLC withfluorescence detection

Pamidronate is a bisphosphonate that is effective in treating bone disease including osteopenia and osteoporosis in adults. A sensitive and reliable method for the analysis of pamidronate in whole blood and urine is key to the development of this drug for use in children. A previously described method for pamidronate analysis serum and urine did not consistently detect the drug at satisfactory levels in whole blood. The procedure involves co-precipitation of the bisphosphonates with calcium phosphate, pre-column derivitization with fluorescamine, HPLC utilizing a Nucleosil C(18) column, and fluorescence detection with excitation at 395 nm and emission at 480 nm. Changes to the original protocol included the use of a new internal standard (alendronate), the optimization of the concentration of ethylenediaminetetraacetic acid (EDTA) for dissolving the precipitate, and the elimination of the acidification step prior to deproteinization. The optimum EDTA concentration, which had a significant effect on the labeling capability of fluorescamine, was determined to be 20 mm.A good separation between pamidronate and alendronate was achieved using a heated (40 degrees C ) Nucleosil C(18), 10 micro m particle size column. The mobile phase was an aqueous solution of 1 mm Na(2)EDTA-methanol (97:3, v/v) adjusted to pH 6.5 using a fl ow-rate of 1 mL/min. Fluorescence detection was set at 395 nm for excitation and at 480 nm for emission. The limit of quantitation for pamidronate was 0.5 micro g/mL in whole blood and 0.1 micro g/mL in urine. The method was applied to both whole blood and urine samples from pediatric patients.

The pharmacokinetics and pharmacodynamics of zoledronic acid in cancer patients with varying degrees of renal function

An open-label pharmacokinetic and pharmacodynamic study of zoledronic acid (Zometa) was performed in 19 cancer patients with bone metastases and known, varying levels of renal function. Patients were stratified according to creatinine clearance (CLcr) into different groups of normal (CLcr > 80 mL/min), mildly (CLcr = 50-80 mL/min), or moderately/severely impaired (CLcr = 10-50 mL/min) renal function. Three intravenous infusions of 4 mg zoledronic acid were administered at 1-month intervals between doses. Plasma concentrations and amounts excreted in urine were determined in all subjects, and 4 patients were administered 14C-labeled zoledronic acid to assess excretion and distribution of drug in whole blood. In general, the drug was well tolerated by the patients. Mean area under the plasma concentration versus time curve and mean concentration immediately after cessation of drug infusion were lower, and mean amounts excreted in urine over 24 hours from start of infusion were higher in normal subjects than in those with impaired renal function (36% vs. 28% of excreted dose), although the differences were not significant. Furthermore, with repeated doses, there was no evidence of drug accumulation in plasma or changes in drug exposure in any of the groups, nor was there any evidence of changes in renal function status. Serum levels of markers of bone resorption (serum C-telopeptide and N-telopeptide) were noticeably reduced after each dose of zoledronic acid across all three renal groups. It was concluded that in patients with mildly to moderately reduced renal function, dosage adjustment of zoledronic acid is likely not necessary.

The effect of intravenous pamidronate on bone mineral density, bone histomorphometry, and parameters of bone turnover in adults with type IA osteogenesis imperfecta

The type IA osteogenesis imperfecta (OI) phenotype is characterized by multiple fractures, blue sclerae, and minimal skeletal deformity without dentinogenesis imperfecta. The object of this study was to determine the effect of treatment with intravenous pamidronate (30 mg) every 3 months on bone density and bone histomorphometry in adults with type IA OI. After an initial iliac crest bone biopsy eight subjects, 5 women and 3 men, entered a treatment program lasting 21-30 months. Five subjects, all women, completed the study which included a posttreatment iliac crest bone biopsy. Pamidronate treatment led to significant increases in bone mineral density (BMD), measured by DXA, in the lumbar spine at 12 months (P = 0.05) and in the femur neck (P = 0.02) at 24 months. Significant increases in BMD were also seen in femoral trochanter at 12 months (P = 0.05) and at 24 months (P = 0.02), and in Ward's triangle at 12 months (P = 0.02) and 24 months (P = 0.05). Mean osteocalcin levels decreased 32%, C-terminal procollagen peptide and bone alkaline phosphatase declined 12% and 47% at 15 and 21 months, respectively. Deoxypyridinoline crosslink excretion decreased 31%. Posttreatment bone biopsy revealed a significant 6.3% increase in mean bone trabecular volume (P = 0.01). Mean cortical thickness increased from 848 mm to 1384 mm (P = 0.01) and cortical porosity decreased 13.2% (P = 0.01). Bone formation rate increased significantly in all 5 patients from 6.6 to 15.3 mm2/yr (P = 0.01). Mineral apposition rate was unchanged. These results indicate that intravenous pamidronate, 30 mg every 3 months, may have significant effects on bone density and histomorphometry in adults with type IA OI. Responses at higher doses remain to be evaluated.

Development and validation of a highly sensitive RIA for zoledronic acid, a new potent heterocyclic bisphosphonate, in human serum, plasma and urine

Zoledronic acid is a new, highly potent bisphosphonate drug under clinical evaluation. A radioimmunoassay has been developed to determine zoledronic acid concentration in human serum, plasma, and urine. The assay utilizes rabbit polyclonal antisera against a zoledronic acid-BSA conjugate and a [125I]zoledronic acid derivative as tracer in a competitive format adapted to microtiter plates. The assay shows a LLOQ 0.4 ng/ml in serum or plasma (interassay%CV=17%, accuracy 97%), 5 ng/ml in urine (21%, 98%). In 23 patients receiving 4, 8 or 16 mg of zoledronic acid, drug concentrations in plasma were dose proportional and showed a multiphasic profile, followed by a prolonged gradual decline to concentrations near the LLOQ. Zoledronic acid disposition in plasma and the recovery of only 40-50% of the dose in urine are consistent with the rapid and extensive uptake by and slow release from bone in parallel with renal clearance, typically shown by bisphosphonates.

Elimination of intravenously administered ibandronate in patients on haemodialysis: a monocentre open study

BACKGROUND

Ibandronate is an inhibitor of osteoclast-mediated bone resorption. This therapeutic effect is utilized in the treatment of osteoporosis and metastatic bone disease. The effect of ibandronate in patients on haemodialysis with renal osteopathy has not been studied since the pharmacokinetics of ibandronate under haemodialysis are unknown.

METHODS

We analysed the removal of ibandronate from the plasma by haemodialysis in 12 chronic haemodialysis patients suffering from end-stage renal disease (ESRD). After intravenous administration of 1 mg ibandronate, the plasma concentration of ibandronate was determined in plasma samples drawn before entering (inflow) and after passing through (outflow) the haemodialyser, and in the dialysate at 1, 2, 3 and 4 h during the first haemodialysis session, and after 1 and 4 h during the second and third dialysis sessions.

RESULTS

The back-extrapolated initial ibandronate plasma level was 38.9+/-15.9 ng/ml; this decreased during first haemodialysis (after 4 h) to 4.9+/-0.9 ng/ml and after two subsequent haemodialysis treatments to 0.38+/-0.16 ng/ml. Ibandronate concentration was reduced by 47% with every passage through the dialyser. The total decrease of ibandronate plasma concentration during the first 4 h of haemodialysis was 78% of plasma peak levels. The ibandronate dialysis plasma clearance was determined at 92+/-19 ml/min. The total amount excreted at the first dialysis using the recovery rate measure was 364+/-98 microg and using the mean difference in inflow/outflow (arteriovenous) concentration (A-V difference method) it was 371+/-132 microg. About 36% of the total amount of ibandronate administered (1 mg) was removed by the first dialysis treatment.

CONCLUSION

Ibandronate was efficiently removed by haemodialysis. After three haemodialysis sessions the ibandronate plasma levels were close to quantification limit. One monthly dose of 1 mg ibandronate would not result in elevated plasma levels in patients with ESRD on haemodialysis treatment three times a week. In haemodialysis patients, ibandronate should be administered after the haemodialysis session.

Interaction of bisphosphonates with calcitonin in monitoring medullary carcinoma of the thyroid

We report the case history of a patient with long standing recurrent medullary carcinoma of the thyroid. Elevation of the serum marker calcitonin coincided with the introduction of biphosphonate therapy and recurrence of tumour was not established. The interaction of biphosphonates with calcitonin is not previously recorded.

New bone-seeking agent: animal study of Tc-99m-incadronate

OBJECTIVE

Disodium cycloheptylaminomethylenediphosphonate monohydrate (incadronate disodium) is a third-generation bisphosphonate compound which potently inhibits bone resorption, and a highly effective drug in the treatment of metastatic bone disease. We first labeled incadronate disodium with 99mTc, and examined its biodistribution and bone uptake after intravenous injection in rats to assess its potential for clinical use as a bone-seeking agent for judgment of the therapeutic effect of incadronate on bone metastases. Bone scan with 99mTc-labeled incadronate (99mTc-incadronate) may yield important information prior to the use of incadronate for treatment of bone metastases.

METHODS

Synthesis of 99mTc-incadronate was carried out by reduction of 99mTc-pertechnetate in the presence of SnCl2 and N2 gas. Normal rats were injected with 18.5 MBq (0.5 mCi) 99mTc-incadronate in a volume of 0.1 ml intravenously and then sacrificed at 15 min, 30 min, 1 h or 2 h (six rats at each time point) after injection. Samples of muscle, stomach, small intestine, kidney, liver and bone (femur) were taken and weighed. In addition, a 1-ml sample of blood was drawn from the heart, and urine was taken from the urinary bladder immediately after sacrifice. Samples were measured for radioactivity and expressed as percent uptake of injected dose per gram or per milliliter (% ID/g or ml). Bone-to-blood and bone-to-muscle uptake ratios were determined from the % ID/g or ml values for these organs.

RESULTS

The greatest accumulation of 99mTc-incadronate was found in bone. Radioactivity in bone was as high as 3.22 +/- 0.68% ID/g at 2 hours after injection. Scintigraphic images of 99mTc-incadronate in normal rats revealed highly selective skeletal uptake.

CONCLUSION

99mTc-incadronate exhibited high uptake in bone, and relatively low uptake in soft tissue, suggesting that it may be useful as a bone-seeking agent for judgment of the therapeutic effect of incadronate on bone metastases, by determining the degree of its accumulation in metastatic bone lesions.

Association between pharmacokinetics of oral ibandronate and clinical response in bone mass and bone turnover in women with postmenopausal osteoporosis

Data from the 1-year, phase II trial of oral ibandronate for treatment of postmenopausal osteoporosis are presented (n = 180). Participants were at least 10 years past menopause and had osteopenia defined as a forearm bone mineral density at least 1.5 SD below the premenopausal mean value. Doses were 0.25, 0.50, 1.0, 2.5, or 5.0 mg daily oral ibandronate or placebo. A total of 116 women treated with ibandronate completed the study. Blood samples for pharmacokinetic analyses were drawn 20 min, 40 min, 60 min, 2 h, 4 h, and 6 h after the first and last administration of the study drug. An enzyme-linked immunosorbent assay was used to determine the concentration of ibandronic acid (BM 21.0955) in serum (Enzymun-Test System ES 600). The assay is based on streptavidine technology to fix the capture antibody to the wall of the tube. Standards were prepared for each participant using individual drug-free serum. The serum concentration-time curves of ibandronate, expressed as the area under the curve over the sampling period (AUC(0-6h)), revealed a highly significant dose-response relationship, p < 0.0001, and linear pharmacokinetic behavior. An initial half-life (T(1/2lambda1)) in serum representing distribution and early elimination was 1.3 hours. Steady-state AUC (AUC(0-6h ss)) increased by a factor of 2.5, which is consistent with an apparent elimination half-life of 32.6 h and a dosing interval of 24 h. There was an exponential association between AUC(0-6h) (ss) and the change from baseline at month 12 in the bone markers (n = 116): r = -0.37 (serum total osteocalcin), r = -0.65 (urine C-telopeptides of type I collagen), and r = -0.65 (serum C-telopeptides of type I collagen), all p < 0.0001. All bone markers were maximally depressed at values of AUC(0-6h ss) of about 3 ng h/mL. AUC(0-6h ss) furthermore revealed a logarithmic association with change from baseline at month 12 in spine BMD, r = 0.39, p < 0.0001. In conclusion, the serum concentration of ibandronate was determined validly by the enzyme-linked immunosorbent assay. The data are the first to show highly significant associations between pharmacokinetic parameters of a bisphosphonate and the clinical response in bone mass and bone turnover.

[Laboratory diagnosis of osteoporosis]

Bone is biologically a highly active tissue whose cells are embedded in a complex network of systemically acting hormones and local mediators. The mechanisms of action involved are as yet only partially understood. With the increase in life expectancy and the resultant change of the population's age structure, diseases of the musculoskeletal system and bones have increased in importance. Thus, research is directed to a greater extent toward bone metabolism and the most frequent bone disease, osteoporosis. Until a few decades ago, the diagnosis of a bone disease was based principally on clinical and radiological methods. Laboratory methods only included the measurement of total alkaline phosphatase activity and calcium and phosphate balance. The development and introduction of new biochemical markers of bone metabolism in recent years led to a considerable increase in available laboratory methods. To evaluate the activity of osteoblastic synthesis, alkaline phosphatase and other bone-forming markers with higher tissue specificity such as bone alkaline phosphatase, osteocalcin, and several collagen propeptides are used. Bone degradation (calcium and hydroxyproline were the only markers until several years ago) can now be detected quickly and reliably with many new serological and urinary markers. Pyridinium derivatives and telopeptides as products of the metabolic activity of osteoclasts have been proved efficacious in diagnosis and therapy control.

Metal-ion speciation in blood plasma incorporating the tetraphosphonate, N,N-dimethylenephosphonate-1-hydroxy-4-aminopropilydenediphosphonate (APDDMP), in therapeutic radiopharmaceuticals

In a quest for more effective radiopharmaceuticals for pain palliation of metastatic bone cancer, this paper relates results obtained with 166Ho and 153Sm complexed to the bone seeking phosphonate, N,N-dimethylenephosphonate-1-hydroxy-4-aminopropylidenediphosphonate (APDDMP). APDDMP is synthesised from the known bone cancer pain palliation agent 1-hydroxy-3-aminopropylidenediphosphonate (APD) and was complexed to lanthanide trivalent metal ions. This work is performed to utilise the idea that the energetic beta-particle emitter, 166 Ho, coupled with phosphonate ligands such as APD and APDDMP could afford a highly effective radiopharmaceutical in the treatment of bone cancer. Complex-formation constants of APDDMP with the important blood plasma metal-ions, Ca2+, Mg2+, and Zn2+ and the trivalent lanthanides Ho3+ and Sm3+ were measured by glass electrode potentiometry at 37 degrees C and I = 150 mM. Blood plasma models were constructed using the computer code ECCLES and the results compared with those gathered from animal tests. The 166Ho-APDDMP complex was found to have little liver or bone uptake while 153Sm-APDDMP had a moderate bone uptake. This was primarily due to the high affinity of APDDMP for Ca(II). Clinical observations could be explained by the blood plasma modelling.

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.

Semi-automatic liquid chromatographic analysis of olpadronate in urine and serum using derivatization with (9-fluorenylmethyl)chloroformate

The semi-automatic bioanalytical assays for olpadronate [(3-dimethylamino-1-hydroxypropylidene)bisphosphonate] involves a protein precipitation with trichloroacetic acid and a double co-precipitation with calcium phosphate for serum samples and a triple calcium co-precipitation for urine samples. These manual procedures are followed by an automated solid-phase extraction on a cation-exchange phase. The procedure is continued either directly, at high olpadronate levels in urine, or after off-line evaporation under nitrogen and reconstitution in water on the same robotic workstation. The continued automatic procedure comprehends derivatization with (9-fluorenylmethyl)chloroformate, ion-pair liquid-liquid extraction and ion-pair HPLC with fluorescence detection at 274/307 nm. The intra- and inter-day precisions for urine and serum samples are typically in the 5-8% range for different olpadronate concentrations [levels near the lower limit of quantification (LLQ) excluded]. The LLQ is 5 ng/ml olpadronate for a 2.5-ml urine sample and 10 ng/ml for a 1-ml serum sample, respectively.

Disposition of tiludronate (Skelid) in animals

The disposition of tiludronate in mouse, rat, rabbit, dog and monkey has been studied after oral and intravenous doses. Like other bisphosphonates, tiludronate was characterized by poor absorption from the gastrointestinal tract. Peak plasma concentrations appeared shortly (0.5-1 h) after dosing, except for the baboon (4.5 h). Food intake highly impaired intestinal absorption The affinity of tiludronate for bone and the slow release from this deep compartment could account for the large volume of distribution and the low plasma clearance found in all species. Tiludronate has low affinity for red blood cells and binds moderately to serum proteins, mainly to serum albumin. Calcified tissues appeared to be the main target for deposition. Distribution into bone was not homogenous, with higher levels in the trabecular bone than in the corticol part of the long bones. The uptake of tiludronate into bone was unequivocally less in the older animal. No metabolism occurred in the tested animal species. The major route of elimination of the absorbed drug is urine. Preclinical observations made with tiludronate, like with other bisphosphonates, were predictive of results obtained in clinical investigation.

Comparison of pharmacokinetics of clodronate after single and repeated doses

OBJECTIVE

Pharmacokinetics of orally given clodronate disodium, a drug for the treatment of hypercalcemia and bone resorption, were studied after a single dose of 400, 800 and 1600 mg given randomly to 11 healthy volunteers in a crossover manner, in 7-14 hospitalized cancer patients given 400, 800 and 1600 mg twice daily, each dosage for one week, and during the customary therapy in 15 additional cancer patients treated in hospital with 400 mg thrice daily for > or = 2 weeks.

METHODS

Clodronate concentrations in serum and urine were measured by capillary gaschromatography with mass-selective detection. Pharmacokinetic parameters were calculated with a three-compartmental model.

RESULTS

After a single oral dose to healthy volunteers the absolute clodronate concentrations increased almost dose-dependently. The mean cumulative excretion in urine was 1.72-2.77% of the dose, an interindividual range being from 0.92% to 5.52%. With 800 and 1600 mg twice daily for one week to cancer patients the serum drug concentrations increased almost progressively with increasing the dose. In cancer patients serum drug concentrations were clearly higher and renal drug clearances (mean 25-62 ml/min) lower than in healthy volunteers (mean 123-149 ml/min). The mean urinary excretions were 2.24-3.14% of the dose and interindividual ranges from 0.18% to 19.0%. During the routine cancer therapy with 400 mg thrice daily, the clodronate excretions in urine on two successive days were on an average 3.26% (range 0.0-10.5%).

CONCLUSIONS

Absolute concentrations in serum and excretions in urine of orally given clodronate increase dose-dependently, but during the maintenance therapy in hospitalized cancer patients the renal drug clearances seem to be lower than in healthy volunteers. This and the large interindividual variation in kinetics propose therapeutic monitoring of clodronate for optimizing the oral dose of the drug.

Double-blind, randomised, placebo-controlled, dose-finding study of oral ibandronate in patients with metastatic bone disease

BACKGROUND

Bisphosphonates are an important component of the treatment of metastatic bone disease but more potent, oral formulations are required to improve the effectiveness and convenience of treatment. An oral formulation of the new bisphosphonate, ibandronate (BM 21.0955) has recently been developed.

PATIENTS AND METHODS

One hundred ten patients with bone metastases (77 breast, 16, prostate, 3 myeloma, 14 others) were recruited from a single institution to this double blind placebo-controlled evaluation of four oral dose levels (5, 10, 20 and 50 mg) of ibandronate. No changes in systemic anti-cancer treatment were allowed in the month before commencing treatment or during the study period. After an initial four-week tolerability phase, patients could continue on treatment for a further three months without unblinding; patients initially allocated to placebo received ibandronate 50 mg. The primary endpoint was urinary calcium excretion (UCCR). Bone resorption was also assessed by measurement of pyridinoline (Pyr), deoxypyridinoline (Dpd), and the N-terminal (NTX) and C-terminal (Crosslaps) portions of the collagen crosslinking molecules.

RESULTS

Two patients did not receive any trial medication thus, 108 patients were evaluable for safety. Ninety-two patients were evaluable for efficacy. A dose dependent reduction was observed in both UCCR and collagen crosslink excretion. At the 50 mg dose level, the percentage reductions from baseline in UCCR, Pyr, Dpd, Crosslaps and NTX were 71%, 28%, 39%, 80% and 74% respectively. One or more gastrointestinal (GI) adverse events occurring in the first month of treatment were reported by six (30%), seven (33%), nine (39%), nine (41%) and eleven (50%) patients at the placebo, 5, 10, 20 and 50 mg dose levels respectively. One patient (20 mg dose) developed radiographically confirmed oesophageal ulceration. GI tolerability may have been adversely affected by concomitant administration of non-steroidal anti-inflammatory agents. Nine (8%) patients stopped treatment within the first month due to GI intolerability but these patients were evenly distributed across the five treatment groups. There was no difference in non-GI adverse events between groups.

CONCLUSIONS

Oral ibandronate has potent effects on the rate of bone resorption at doses which are generally well tolerated. Further development is appropriate to evaluate the effects of long-term administration in the prevention of metastatic bone disease and the management of established skeletal metastases.

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.

[Factors that determine intensity of response to treatment with tiludronate in Paget's disease]

OBJECTIVE

To investigate the influence of both clinical and pharmacokinetic factors as determinants of response to tiludronate in Paget's bone disease (PBD).

PATIENTS AND METHODS

Twenty six PBD patients with serum alkaline phosphatase (SAP) levels at least twice the normal upper limit were enrolled. The sample included 17 (65%) men and 9 (35%) women whose mean age (SD) was 60.3 (9.8) (range: 38-76). Each patient received 400 mg/day of tiludronate, per os, for 90 (6) days. The SAP variations were considered as the main parameter of response. Plasma concentrations of tiludronate were assayed using the HPLC method with UV detection; the maximum and minimum (Cmin) concentration, as well as the area under a concentration-time curve were calculated. Multivariate regression analysis was performed to assess the influence on tiludronate effect.

RESULTS

Mean (SD) percent reduction of SAP from the initial values ranged from 30.5 (13.9) at the end of the first month of drug intake to a nadir of 76.1 (8.8) achieved 6 months after the treatment was stopped. Serum SAP activity fell to normal range in 7 (27%) patients at the end of the therapy period, in 17 (65%) three months later, and in 18 (69%) one year thereafter. One year after the treatment ended only one patient had evidence of relapse. Final multivariate regression model showed that the percent reduction of SAP increases by 11.9 percent points per Cmin tiludronate unit and by 0.006 points per basal SAP unit, and decreases by 0.52 per year of age. Out of 13 patients with bone pain, 9 (69%) experienced relief within the second and third months of treatment. No clinical or laboratory severe side effects were seen and only five patients (19%) had mild adverse events.

CONCLUSIONS

These results confirm that tiludronate leads to a marked suppression of PDB clinical and biochemical activity. Cmin of tiludronate in plasma is the best predictor of biochemical response.

Semi-automatic liquid chromatographic analysis of pamidronate in serum and citrate plasma after derivatization with 1-naphthylisothiocyanate

The semi-automatic method for the determination of the bisphosphonate pamidronate in serum and citrate plasma involves a manual protein precipitation with trichloroacetic acid and a manual coprecipitation of the bisphosphonate with calcium phosphate, followed by an automated solid-phase extraction on anion-exchange columns. After off-line evaporation of the extract under nitrogen and reconstitution in water, the automatic procedure is continued by automatic derivatization with 1-naphthylisothiocyanate, ion-pair liquid-liquid extraction and a treatment with hydrogen peroxide, prior to analysis by ion-pair HPLC and fluorescence detection at 285/390 nm. The intra- and inter-day precisions are 1.3 and 7%, respectively, for a standard of 100 ng ml(-1) pamidronate in serum; the average accuracy for this standard is 107%. The lower limit of quantification is 20 ng ml(-1) pamidronate in 1 ml of human serum.

Detection of sarin hydrolysis products from sarin-like organophosphorus agent-exposed human erythrocytes

A sarin-like organophosphorus agent, [bis(isopropyl methyl)phosphonate; BIMP], was synthesized. This agent has the same phosphonate group as sarin and also has the same anti-acetylcholinesterase activity potency as sarin. The ID50 and LD50 values of BIMP in mice after intravenous injection were 3.9 nM and 0.8 mg/kg, respectively. The AChE activities of their red blood cells and brains were dose-dependently reduced by intravenous BIMP. After preparation of experimental BIMP-exposed human red blood cells, BIMP-bound acetylcholinesterase (AChE) was solubilized from erythrocyte membranes, purified by immunoaffinity chromatography, digested with trypsin, and the sarin hydrolysis products bound to AChE were released by alkaline phosphatase digestion. The digested sarin hydrolysis products were subjected to trimethylsilyl (TMS) derivatization and detected by gas chromatography-mass spectrometry. Isopropyl methylphosphonic- and methylphosphonic acids, which are the sarin hydrolysis products, were detected in experimental BIMP-exposed human red blood cells. This new method, which enables sarin's hydrolysis products to be detected in BIMP-exposed erythrocytes, is a useful tool for studying sarin-poisoning victims.

Comparison of the efficacy and bioequivalence of two oral formulations of tiludronate in the treatment of Paget's disease of bone

Tiludronate, an oral bisphosphonate used to treat Paget's disease of bone, is currently being studied as a treatment for osteoporosis. A multicenter, open-label, parallel-group study was performed to compare the efficacy of two tablet formulations of tiludronate in the treatment of Paget's disease. Eighty-eight patients with active Paget's disease were recruited. The diagnosis was based on radiologic evidence of bone lesions, and all patients included in the study had serum alkaline phosphatase (SAP) levels equal to or more than twice the upper normal value of the local laboratory that assayed the sample. Each patient received treatment with oral tiludronate 400 mg/d for 84 +/- 2 days; 39 patients received the previously tested tablet formulation 3C1, and 49 patients received formulation 9O1, which is prepared using an improved manufacturing technique. The objective of this study was to determine whether the two formulations have an equivalent therapeutic effect, the primary end point being SAP levels in both groups after 3 months of treatment. This equivalence is commonly assessed by comparing pharmacokinetic data; however, in previous studies of tiludronate, large intra-individual variability prevented statistically valid comparisons of the data. Therefore, in addition to pharmacokinetic data, biochemical and clinical response data were collected during the trial. The secondary objectives of the trial were to measure the plasma levels and to assess the efficacy and safety of the two tiludronate formulations. The relative pharmacologic activities of the two formulations were assessed by comparison of the confidence intervals of levels of SAP at monthly intervals. After 3 months of treatment, the 90% confidence interval of the difference between the formulations was included in the reference confidence interval. These findings suggest that the 9O1 and 3C1 formulations did not show a significant difference in therapeutic activity. Furthermore, after 3 months of treatment, the frequency of normalization of SAP levels was 30.6% in the 9O1 treatment group and 28.2% in the 3C1 treatment group. The percentage of patients responding to treatment (defined as a decrease in SAP levels of at least 50% from baseline) was 67.3% in the 9O1 treatment group and 69.2% in the 3C1 treatment group. Statistical analyses performed on the maximum and minimum plasma concentrations of tiludronate showed no significant differences between the two formulations. In this trial, the two tablet formulations of tiludronate demonstrated therapeutic and pharmacokinetic equivalence.

An enzyme inhibition assay for the quantitative determination of the new bisphosphonate zoledronate in plasma

Zoledronate, 2-(imidazole-1-yl)-1-hydroxyethane-1,1-bisphosphonic acid is a new 3rd generation bisphosphonate. A specific enzyme inhibition assay was developed for the determination of zoledronate in plasma of animals and man. The multistep synthesis of cholesterol and some of its precursors (lanosterol, squalene) from 14C-labeled mevalonic acid lactone is catalyzed by the S12 fraction of homogenized rat liver in the presence of ATP, NADH and Mg2+. After hydrolysis of the reaction mixture with KOH, lipophilic reaction products were extracted with hexane and the overall yield determined by radiometry. Addition of zoledronate inhibited the formation of cholesterol and its precursors in a dose dependent manner. The described method is suitable to specifically and quantitatively measure concentrations of zoledronate down to 25 ng ml-1 in human and animal (dog, rat) plasma with acceptable reproducibility and accuracy.

Pharmacokinetics of incadronate, a new bisphosphonate, in healthy volunteers and patients with malignancy-associated hypercalcemia

We investigated the pharmacokinetics of incadronate, a new bisphosphonate, after a 2-hour intravenous infusion to healthy volunteers and patients with malignancy-associated hypercalcemia. Following administration at 0.025-1.6 mg to healthy volunteers, peak plasma concentration of incadronate increased in a dose-proportional manner. Plasma concentration thereafter declined biexponentially with a half-life of 0.26-0.40 h (t1/2 alpha) and 1.58-1.98 h (t1/2 beta). AUC increased dose-proportionally, whereas distribution volume (Vdss), total body clearance (CLt), renal clearance (CLr) and nonrenal clearance (CLnr), corresponding to bone uptake clearance, changed little among doses, indicating the linear pharmacokinetics of the drug after intravenous administration. Within 24 h, 55.1-69.5% of the dose was excreted into urine as the unchanged drug, most in the first 6 h. CLr and CLnr accounted for about 60% and 40% of the CLt, respectively, suggesting that the pharmacokinetics of incadronate are affected by changes in these clearances. In patients, plasma concentration at 2 h increased dose-proportionally in the range of 2.5-10.0 mg. Urinary excretion of YM175 up to 24 h after dosing was as low as 10.5% of the dose, being 1/6 of those in volunteers. A positive correlation (r > 0.89) was observed between creatinine clearance and urinary incadronate excretion in all volunteers and patients, indicating that the reduction of urinary excretion in patients is due to the decrease in renal function accompanying hypercalcemia. Based on comparison of the dose-normalized plasma concentration, the plasma level at 2 h in patients was comparable with that in volunteers, whereas the level at 8 h was 3 times higher in patients, suggesting that elimination from plasma in patients is delayed due to decreased renal function. Nevertheless, the plasma concentration profile in patients was lower than that predicted from the decrease in CLr. This finding suggests that the increase in plasma concentration with decreasing renal excretion in hypercalcemic patients was compensated for by enhanced bone uptake of the drug.

Five phase bone scintigraphy supports the pathophysiological concept of a subclinical inflammatory process in reflex sympathetic dystrophy

This study evaluates quantitative and qualitative patterns of bone scintigraphy and correlates them to laboratory findings and clinical signs to reveal possible inflammatory reactions in RSD. Activity ratios between the affected hand/foot and the contralateral side were calculated in 99mTc DPD-bone scintigraphy for five phases (arterial: 0-30 sec, early blood pool: 0.5-5 min. late blood pool: 5-15 min, 3 hrs early bone, 24 hrs late bone phase) and the presence of five scintigraphic signs in the bone phases was assessed. Activity ratios of all phases correlated with ESR those in the early and late bone phase correlated with alpha 2 globulin and beta globulin concentrations and those in the arterial, the early and late blood pool phase with the gamma globulin concentrations, respectively. Clinical features such as pain, swelling, physical force, temperature differences and the duration of symptoms did not correlate to the activity ratios. However, three signs in the bone phase were negatively correlated to albumin concentrations. Positive correlations were found for alpha 2, gamma globulin concentrations, ESR, neutrophil cell counts and individual uptake patterns. We conclude that the quantitative analysis of five phase bone scintigraphy in RSD reveals different aspects of tracer kinetics and provides different pathophysiological information. Lateralization of regional hyperemia, increased micro vascular permeability and bone metabolism in RSD parallels shifts in protein concentrations and blood cell counts that are suggestive of a subacute inflammatory process, even in patients with no overt signs of inflammation.

Accumulation of bisphosphonates in the aorta and some other tissues of healthy and atherosclerotic rabbits

Clodronate, etidronate, and pamidronate are highly hydrophilic bisphosphonates used for the treatment of bone resorption and hypercalcemia. They also inhibit the development of experimental atherosclerosis without influencing serum cholesterol level. We studied the distribution and the accumulation of the carbon 14-labeled bisphosphonates in the aorta and some other tissues of healthy rabbits and in rabbits with diet-induced atherosclerosis. After intravenous injection, clodronate and pamidronate disappeared from circulation more slowly in atherosclerotic than in healthy rabbits, and the drug concentrations in the peripheral tissues were generally lower in atherosclerotic than in healthy animals. At 24 hours after dosing in healthy rabbits, the mean aorta to plasma ratios of clodronate, etidronate, and pamidronate were, respectively, 2.4 to 2.8, 2.4 to 4.0, and 8.6 to 10. The corresponding ratios in atherosclerotic rabbits were, respectively, 13 to 22, 1.5 to 2.2, and 13 to 24. Seven days after the injection the mean clodronate concentration in the aortas of healthy rabbits was 0.5% to 0.9% of the dose given per tissue weight, and the concentration in those of atherosclerotic animals was 3.8% to 5.2% of the dose given per tissue weight. The results indicate that hydrophilic bisphosphonates, known to inhibit the atherogenesis, concentrate markedly in the aortas of healthy and atherosclerotic rabbits.

Human pharmacokinetics of tiludronate

Tiludronate is a bisphosphonate evaluated extensively as an osteoregulator in the treatment of metabolic bone disorders. It is highly polar and has a low and variable oral absorption similar to its related compounds. An absolute bioavailability of approximately 6% has been reported with large inter- and intra-subject variability. The extent of absorption is increased at doses above 400 mg and may be reduced by a factor of 5 when tiludronate is administered with, or within 2 h after, food or dairy products. Approximately 90% of tiludronate is bound to serum albumin, and the binding is linear in the concentration range 1-10 mg/L. Preliminary in vitro studies using human hepatocytes failed to show any evidence of biotransformation of tiludronate. The elimination half-life in patients with normal renal function is approximately 40-60 h, but is significantly increased in subjects with severe renal impairment. The renal clearance (0.7 L/h) is independent of dose and suggests that glomerular filtration is the mechanism responsible for elimination. Approximately 50% of the absorbed dose is bound to bone and the rate of release of the drug from this site is limited by bone turnover. In vitro experiments indicate that tiludronate is not an enzyme inducer or inhibitor. Drug interaction studies with the nonsteroidal agents acetylsalicylic acid, indomethacin, and diclofenac indicate that only with indomethacin was there any change in the pharmacokinetic parameters, and that these changes were minimal and unlikely to be of clinical significance. Tiludronate does not influence the pharmacokinetics of digoxin at steady state. Tiludronate appears to exhibit similar pharmacokinetic behavior to other bisphosphonates with the exception that its absolute bioavailability is significantly higher than that previously reported for clodronate and pamidronate. The impact of its pharmacokinetic properties on clinical outcome has yet to be determined.

Selective and sensitive determination of pamidronate in human plasma and urine by gas chromatography with flame photometric detection

A rapid, selective and sensitive method for the determination of pamidronate in human plasma and urine samples by gas chromatography (GC) has been developed. After deproteinization of the sample with trichloroacetic acid, pamidronate was converted into its N-isobutoxycarbonyl methyl ester derivative and measured by GC with flame photometric detection (FPD), using a HP-1 capillary column. The derivative preparation and GC analysis were accomplished within 30 min. The derivative was sufficiently volatile and stable, giving a single and symmetrical peak, and provided an excellent FPD response. The detection limit of pamidronate, at a signal-to-noise ratio of 3, was ca. 100 pg injected, and the calibration curve for this compound in the range 20-1000 ng was linear and sufficiently reproducible for quantitative determination. This method could be successfully applied to plasma and urine samples without a preliminary clean-up except for deproteinization with trichloroacetic acid, and pamidronate could be measured without any influence from coexisting substances. Overall recoveries of pamidronate added to plasma and urine samples were 93-97%. The coefficients of variation for intra-assay and inter-assay of pamidronate in these samples were 1.0-7.9% (n = 3) and 4.1-8.3% (n = 6), respectively.

On the absorption of alendronate in rats

Alendronate is an antiosteolytic agent under investigation for the treatment of a number of bone disorders. Since the compound is a zwitterion with five pKa values and is completely ionized in the intestine at the physiological pH, absorption is poor; less than 1% of an oral dose is available systemically in rats. In the present studies, absorption was found to be predominantly in the upper part of the small intestine. Administration of buffered solutions of alendronate (pH 2-11) did not improve absorption. Whereas food markedly impaired the absorption of alendronate, EDTA enhanced absorption in a dose-dependent manner. Pretreatment of rats with ulcerogenic agents, mepirizole, acetylsalicylic acid, or indomethacin, resulted in a 3-7-fold increase in the oral absorption of alendronate. The absorption of phenol red, added as an indicator of intestinal tissue damage, was also increased in rats with experimental peptic ulcers. The enhanced absorption of alendronate observed in rats with experimental peptic ulcers was attributed to the alteration of the integrity of the intestinal membrane.

Nonlinear kinetics of alendronate. Plasma protein binding and bone uptake

Alendronate (4-amino-1-hydroxybutylidene-1,1-bisphosphonate), an antiosteolytic agent, is currently under investigation in the treatment of osteoporosis. The purpose of this study was to examine the plasma protein binding and the ability of bone to bind alendronate, and their effects on the distribution of the drug to bone tissues. In addition, the species differences in plasma protein binding and bone uptake between rats and dogs were studied. Following intravenous administration (0.8 or 1 mg/kg), the apparent uptake clearance (CL,up) by tibia in dogs and rats was approximately 0.075 and 0.18 ml/min/g bone tissue, respectively. The binding of alendronate to plasma protein was species-dependent; the drug was highly bound to rat plasma, but not to dog plasma. The unbound fraction of alendronate was approximately 0.03 for the rat and 0.53 for the dog. Binding studies with purified serum albumin revealed the presence of displacer(s) in dog plasma. This may explain the low binding of alendronate in dog plasma. Like other organs, uptake of drugs by bone tissue is controlled by the plasma flow (Q), the fraction of unbound drug in plasma (fp), and the intrinsic ability of bone to bind the drug (CLin) as described by the equation: CL,up = Q(1-e-tp.CLin/Q). Plasma flow to the tibia of dogs and rats is reported to be approximately 0.09 and 0.25 ml/min/g, respectively. By applying the equation, the CLin was estimated to be approximately 10 ml/min/g for the rat and 0.3 ml/min/g for the dog. These results indicate that both plasma protein binding and bone uptake were species-dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of diffuse skeletal lesions by monitoring the kinetics of labeled phosphonate

A method of detecting of diffuse skeletal involvement in patients with metastatic tumors or with metabolic diseases is presented. The study consisted of 31 patients without bone disease and of 26 selected patients with diffuse skeletal involvement. The kinetics of 99mTc-dicarboxypropane diphosphonate (DPD) were calculated by monitoring the plasma and urine concentrations up to 5 hours after administration. Using these data, the renal clearance as well as the increase in urinary excretion of 99mTc-DPD were determined. The results indicate that measurement of the quantity of 99mTc-DPD excreted in the urine after 3 hours allows a reliable separation of the patients with diffuse skeletal lesions from normals. Other calculations such as renal clearance as well as the drop in plasma concentration were less sensitive. The test may be performed simultaneously with bone scintigraphy without additional radiation burden to the patient.

Sensitive determination of a novel bisphosphonate, YM529, in plasma, urine and bone by high-performance liquid chromatography with fluorescence detection

A high-performance liquid chromatographic method for the sensitive determination of 1-hydroxy-2-(imidazo[1,2-a]pyridin-3-yl)ethane-1, 1-bisphosphonic acid monohydrate (YM529) in plasma, urine and bone is described. Plasma obtained in high-dose animal studies is treated by method A, a simple method using 1 ml of plasma, which is based on deproteinization of plasma followed by coprecipitation of the drug with calcium phosphate and dissolution of the precipitate in EDTA. Plasma obtained in low-dose clinical studies is treated by method B, a more sensitive method using 4 ml of plasma, which is based on direct precipitation of the drug prior to the deproteinization in method A. Urine and bone samples are prepared by solid-phase extraction using a Sep-Pak C18 cartridge coupled with method A. The drug is separated with a reversed-phase column using a mobile phase at pH 7, and detected with a fluorescence detector following postcolumn alkalization of the mobile phase to enhance fluorescence intensity. The limit of determination is 0.2 ng/ml for method A and 0.05 ng/ml for method B in plasma, 0.05 ng/ml in urine, and 5 ng/g in bone.

Role of calcium in plasma protein binding and renal handling of alendronate in hypo- and hypercalcemic rats

Alendronate (4-amino-1-hydroxybutylidine-1,1-bisphosphonate), an antiosteolytic agent, is currently under investigation for the treatment of osteoporosis. Earlier studies in animals from this laboratory disclosed that systemically administered alendronate is rapidly taken up by bone tissues to the extent of 60% to 70% of the dose and excreted by the kidney, 30% to 40% in 24 hr, and that renal excretion is the only route of elimination. This study was designed to explore the effect of calcium on plasma protein binding and the renal handling of alendronate. The binding of alendronate to rat plasma was concentration, pH and calcium dependent. The fraction of unbound drug in rat plasma increased from about 3% to 9% over a drug concentration range of 0.2 to 10 micrograms/ml. Supplementation of calcium strongly augmented the binding to serum albumin. The binding of alendronate in plasma increased with increasing pH from about 50% at pH 6.6 to 98% at pH 8.6. The effects of pH on the binding of calcium and of alendronate to serum albumin were qualitatively similar. Under steady-state conditions, the binding of alendronate was substantially lower in hypocalcemic rats but unchanged in hypercalcemic rats. Although hypocalcemia caused a significant decrease in the renal secretion of alendronate, there was no effect on the renal secretion of tetraethylammonium bromide and p-aminohippuric acid. The differential effect of hypocalcemia suggests that calcium may play an important role in the renal handling of alendronate. However, hypercalcemia resulted in a substantial decrease of renal secretion of all three compounds and the decreased renal secretion was associated with a marked decrease in the glomerular filtration rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Uptake of alendronate by bone tissue in hypocalcemic and hypercalcemic rats

Alendronate (4-amino-1-hydroxybutylidene-1,1-bisphosphonate), an antiosteolytic agent, is currently under investigation in the treatment of osteoporosis. Earlier studies in rats from this laboratory have demonstrated that systemically administered alendronate was taken up by bone tissues to the extent of 60-70% of the dose and excreted by the kidneys, 30-40%, and that renal excretion was the only route of elimination of the drug. In this study, a classic three-compartment model was used to determine the kinetics of bone uptake of alendronate in hypo- and hypercalcemic rats. Following intravenous administration (1 mg/kg), the apparent uptake clearance (CL,up) by tibia was approximately 0.18 ml/min/g of bone for control rats, 0.25 ml/min/g for hypocalcemic rats, and 0.05 ml/min/g for hypercalcemic rats. Like other organs, uptake of drugs by bone tissues would be controlled by the plasma flow rate (Q), the fraction of unbound drugs in plasma (fp), and the intrinsic ability of bone uptake (CLin) as described by the equation: CL,up = Q(1 - e-fp.CLin/Q). The plasma flow rate to the tibia of rats was reported to be approximately 0.25 ml/min/g. The unbound fraction of alendronate in plasma of control, hypo-, and hypercalcemic rats was 0.03, 0.45, and 0.035, respectively. By applying the equation, the intrinsic ability (CLin) of bone uptake was estimated to be approximately 10, 2.3, and 1.6 ml/min/g for control, hypo-, and hypercalcemic rats, respectively, indicating that the intrinsic ability of bone to bind alendronate was decreased in both hypo- and hypercalcemic rats.

Determination of a new bisphosphonate, YM175, in plasma, urine and bone by high-performance liquid chromatography with electrochemical detection

A high-performance liquid chromatographic method for the determination of disodium dihydrogen(cycloheptylamino)methylene-bisphosphonate monohydrate (YM175) in plasma, urine and bone is described. Plasma obtained in high-dose animal studies is pretreated by Method A, a simple method using 1 ml of plasma, which is based on deproteinization of plasma followed by coprecipitation of the drug with calcium phosphate and removal of excess calcium ions by AG 50W-X8 resin. Plasma obtained in lower-dose clinical studies is treated by Method B, a more sensitive method using 10 ml of plasma, which is based on solid-phase extraction using a Sep-Pak C18 cartridge coupled with Method A. Urine and bone are treated similarly to Method B. The chromatographic system consists of a mobile phase at pH 11, an alkali-stable column and an electrochemical detector operating in the oxidation mode. The determination limit is 5 ng/ml for Method A and 0.5 ng/ml for Method B in plasma, 1 ng/ml in urine, and 25 ng/g in bone.

Improved determination of the bisphosphonate alendronate in human plasma and urine by automated precolumn derivatization and high-performance liquid chromatography with fluorescence and electrochemical detection

An improved method for the determination of 4-amino-1-hydroxybutane-1,1-bisphosphonic acid (alendronate) in human urine and an assay in human plasma are described. The methods are based on co-precipitation of the bisphosphonate with calcium phosphates, automated pre-column derivatization of the primary amino group of the bisphosphonic acid with 2,3-naphthalene dicarboxyaldehyde (NDA)-N-acetyl-D-penicillamine (NAP) or cyanide (CN-) reagents, and high-performance liquid chromatography (HPLC) with electrochemical (ED) or fluorescence detection (FD). The feasibility of ED of the NDA-CN- derivative of aldendronate has been demonstrated, and a HPLC-ED assay in human urine has been validated in the concentration range 2.5-50.0 ng/ml. In order to eliminate the cyanide ion from the assay procedure, several other nucleophiles in the NDA derivatization reaction were evaluated. An NDA-NAP reagent was found to produce highly fluorescent derivatives of alendronate. The assay in urine based on NDA-NAP derivatization and HPLC-FD has been developed and fully validated in the concentration range 1-25 ng/ml. Based on the same NDA-NAP derivatization, an assay in human plasma with a limit of quantification of 5 ng/ml has also been developed. Both HPLC-FD assays were utilized to support various human pharmacokinetic studies with alendronate.

Pharmacokinetics of pamidronate in patients with bone metastases

BACKGROUND

Pamidronate is a second-generation bisphosphonate used in the treatment of tumor-induced hypercalcemia and in the management of bone metastases from breast cancer, myeloma, or prostate cancer. The pharmacokinetics of pamidronate is unknown in cancer patients.

PURPOSE

To determine the influence of the rate of administration and of bone metabolism, we studied the pharmacokinetics of pamidronate at three different infusion rates in 37 patients with bone metastases.

METHODS

Three groups of 11-14 patients were given 60 mg pamidronate as an intravenous infusion over a period of 1, 4, or 24 hours. Urine samples were collected in the three groups of patients. Plasma samples were obtained only in the 1-hour infusion group. The assay of pamidronate in plasma and urine was performed by high-performance liquid chromatography with fluorescence detection after the derivatization of pamidronate with fluorescamine.

RESULTS

The body retention (BR) at 0-24 hours of pamidronate represented 60%-70% of the administered dose and was not significantly modified by the infusion rate. In particular, the BR at 0-24 hours was not reduced at the fastest infusion rate. Among patients, a threefold variability in BR at 0-24 hours occurred, which was related directly to the number of bone metastases and, to some extent, to creatinine clearance. At 60 mg/hour, the plasma kinetics followed a multiexponential course characterized by a short distribution phase. The mean (+/- SD) half-life of the distribution phase was 0.8 hour (+/- 0.3), the mean (+/- SD) of the area under the curve for drug concentration in plasma x time at 0-24 hours was 22.0 +/- 8.8 mumol/L x hours, and the mean (+/- SD) of the maximum plasma concentration was 9.7 mumol/L (+/- 3.2). Pharmacokinetic variables remained unchanged after repeated infusions applied to four patients. Clinically, the three infusion rates were equally well tolerated without significant toxicity.

CONCLUSIONS

The 1-hour infusion rate could be proposed as kinetically appropriate for the administration of pamidronate to patients with metastatic bone diseases.

Plasma protein binding of APD: role of calcium and transferrin

The bisphosphonate drug APD (pamidronate, 3-amino-1-hydroxypropylidene-1,1-bisphosphonate) has been shown to bind to human plasma proteins. This was an unexpected observation since this hydrophilic, anionic drug is not typical of molecules that exhibit this characteristic. At a concentration of 5 micrograms/ml the extent of binding of APD to fresh human plasma in vitro was variable between subjects 30.2% +/- 8.5% (mean +/- S.D., n = 10). Binding was not influenced by the time or concentration of APD over the range 0.05-10.0 micrograms/ml. At 20 and 50 micrograms/ml some precipitation of APD occurred. Both calcium and iron play a role in the binding of APD to plasma proteins, addition of calcium to plasma increased the degree of binding of APD, whereas the calcium chelators EDTA and EGTA reduced the binding of APD. Similarly, addition of iron to plasma increased the binding and the inclusion of the iron chelator desferrioxamine diminished the binding of the drug. The effects of iron and desferrioxamine were less pronounced than those of calcium and EDTA, indicating that the majority of the binding involves calcium ions and a smaller contribution is made by ferric ions. The equilibrium dissociation constants (Kd) for APD binding to calcium and iron binding sites on plasma proteins were estimated to be 852 microM and 29 microM, respectively. Calcium binding sites were of high capacity but low affinity and the iron binding sites were of lower capacity and higher affinity. Electrophoresis of plasma proteins following incubation with [14C]APD revealed binding to the transferrin and globulin fractions. However, there was some dissociation of protein bound APD during the electrophoresis. The consequences of hypercalcaemia on the pharmacokinetics of APD are discussed.

The pharmacokinetics and distribution of pamidronate for a range of doses in the mouse

The pharmacokinetics of the bisphosphonate drug pamidronate (APD, 3-amino-1-hydroxypropylidene-1,1-bisphosphonate) have been investigated in the mouse by using 14C-APD and following the tissue concentrations for up to 90 days postdose. The accumulation of APD in bone was the highest of all tissues and was linear with increasing dose up to the maximum dose employed (30 mg/kg), which is indicative of the uptake process being a simple chemical phenomenon. Despite the known effects of APD on bone turnover rates and osteoclast activity, the dose appeared to have no significant influence on the biological half-life of APD in bone which was found to be 90-140 days. A high dose of APD (5 mg/kg) appeared to prolong its uptake phase by bone, however, a net movement of APD from the soft tissues is the likely explanation for this finding. The concentrations of APD in the soft tissues investigated (liver, spleen, kidney, lung, and muscle) declined in a biphasic manner, initially in parallel with the fall in the plasma concentration and followed by a gradual fall in APD's concentration in the soft tissues due to renal elimination and a redistribution favoring the calcified tissues. The liver and spleen contained higher concentrations of APD relative to the other soft tissues. The 0-24 hour renal excretion of APD was found to fall with increasing dose above 2.5 mg/kg; this may be due to either nephrotoxicity or increased uptake by soft tissues. For doses over 20 mg/kg, there was some evidence of nephrotoxicity. The data from these studies have been used to formulate a simple physiological model for APD disposition.

Improved determination of the bisphosphonate pamidronate disodium in plasma and urine by pre-column derivatization with fluorescamine, high-performance liquid chromatography and fluorescence detection

An improved method for the determination of 1-hydroxy-3-aminopropylidene-1,1-bisphosphonate (pamidronate) in human urine and plasma is described. The procedure is based on a co-precipitation of the bisphosphonates (pamidronate and 6-amino-1-hydroxypentilidene-bisphosphonate, used as internal standard) with calcium phosphate. After centrifugation the precipitate is redissolved in hydrochloric acid, followed by a second precipitation. Then the bisphosphonates are dissolved in ethylenediaminetetraacetic acid, derivatized with fluorescamine, and separated by high-performance liquid chromatography. Using fluorescence detection, the limit of quantitation for pamidronate was 0.8 mumol/l in plasma and 0.7 mumol/l in urine.

Determination of 4-amino-1-hydroxybutane-1,1-bisphosphonic acid in urine by automated pre-column derivatization with 2,3-naphthalene dicarboxyaldehyde and high-performance liquid chromatography with fluorescence detection

A sensitive (5 ng/ml) method for the determination of 4-amino-1-hydroxybutane-1,1-bisphosphonic acid in human urine is described. The procedure includes (1) the isolation of the drug from urine by co-precipitation of its calcium salt with endogenous phosphates in the presence of base, (2) a solid-phase anion-exchange sample clean-up and (3) automated pre-column derivatization of the primary amino group with 2,3-naphthalene dicarboxyaldehyde-cyanide reagent followed by fluorescence detection of the N-substituted cyanobenz[f]isoindole derivative. The derivative of the drug was synthesized and its spectral and fluorescence properties were evaluated. The fluorescence quantum efficiency was determined to be 0.82 in the mobile phase used for the assay. The derivative is also capable of accepting energy in an oxalate ester-hydrogen peroxide chemiluminescence system.

Determination of belfosdil, a new calcium channel blocker, in human plasma by capillary gas chromatography with nitrogen-phosphorus detection

Belfosdil and the internal standard were extracted from human plasma by a double liquid-liquid extraction. After a concentration step, gas chromatographic analysis of the sample was performed using a capillary fused-silica column and a nitrogen-phosphorus detector. The limit of detection of belfosdil was 0.025 ng/ml and the standard curve was linear over the range 0.05-100 ng/ml. The intra-assay and inter-assay precisions were within 7% (relative standard deviation) and the intra-assay and inter-assay accuracy values deviated by less than 5%. The extractability of belfosdil was 79%. The assay method was successfully used for the analysis of plasma samples from clinical studies with dose ranges of 5-100 mg of belfosdil.