Proline modulates the effect of bisphosphonate on calcium levels and adenosine triphosphate production in cell lines derived from bovine Echinococcus granulosus protoscoleces.

Bisphosphonates have been proposed as pharmacological agents against parasite and cancer cell growth. The effect of these compounds on helminthic cell viability and acellular compartment morphology, however, has not yet been studied. The effects of different types of bisphosphonates, namely etidronate (EHDP), pamidronate (APD), alendronate (ABP), ibandronate (IB) and olpadronate (OPD), and their interaction with amiloride, 1,25-dihydroxycholecalciferol (D3) and proline were evaluated on a cell line derived from bovine Echinococcus granulousus protoscoleces (EGPE) that forms cystic colonies in agarose. The EGPE cell line allowed testing the effect of bisphosphonates alone and in association with other compounds that could modulate calcium apposition/deposition, and were useful in measuring the impact of these compounds on cell growth, cystic colony formation and calcium storage. Decreased cell growth and cystic colony formation were found with EHDP, IB and OPD, and increased calcium storage with EHDP only. Calcium storage in EGPE cells appeared to be sensitive to the effect of amiloride, D3 and proline. Proline decreased calcium storage and increased colony formation. Changes in calcium storage may be associated with degenerative changes of the cysts, as shown in the in vitro colony model and linked to an adenosine triphosphate (ATP) decrease. In conclusion, bisphosphonates could be suitable tempering drugs to treat cestode infections.

Mineralization- and remodeling-unrelated improvement of the post-yield properties of rat cortical bone by high doses of olpadronate.

Some pharmacologic effects on bone modeling may not be evident in studies of remodeling skeletons. This study analyzes some effects of olpadronate on cortical bone modeling and post-yield properties in femurs diaphyses (virtually only-modeling bones) of young rats by mid-diaphyseal pQCT scans and bending tests. We studied 20/22 male/female animals traetad orally with olpadronate (45-90 mg/kg/d, 3 months) and 8/9 untreated controls. Both OPD doses enhanced diaphyseal cross-sectional moments of inertia (CSMI) with no change in cortical vBMD and elastic modulus. Yield stiffness and strength were mildly increased. Post-yield strength, deflection and energy absorption were strikingly enhanced. Ultimate strength was enhanced mainly because of effects on bone mass/geometry and post-yield properties. The large improvement of post-yield properties could be explained by improvements in bone geometry. Improvements in bone mass/geometry over weight-bearing needs suggest an enhanced modeling-related response to mechanical stimuli. Effects on tissue microstructural factors (not measured) could not be excluded. Results reveal novel olpadronate effects on bone strength and toughness unrelated to tissue mineralization and stiffness, even at high doses. Further studies could establish whether this could also occur in modeling-remodeling skeletons. If so, they could counteract the negative impact of anti-remodeling effects of bisphosphonates on bone strength.

Biomechanical background for a noninvasive assessment of bone strength and muscle-bone interactions.

New concepts and methods of study in bone biomechanics defy the prevailing idea that bone strength is determined by a systemically-controlled "mineralized mass" which grows until reaching a peak and then is lost at individually-specific rates. In case of bones, "mass" represents actually the substratum of a structure, the stiffness of which does not depend on the mass, but on the intrinsic stiffness and the spatial distribution of the mineralized material. A feed-back system called "bone mechanostat" seems to orient the osteoblastic and osteoclastic processes of bone, modeling and remodeling, according to the sensing by osteocytes of strains caused in the structure by mechanical usage of the skeleton, in specific directions as determined principally by the customary contractions of regional muscles and impact forces. The endocrine-metabolic systems, crucial for the normal skeletal development, modulate the work of osteocytes, blasts and clasts in a systemic way (i.e., not related to a specific direction of the stimuli). Therefore, they tend actually to interact with, rather than contribute to, the biomechanical control of bone structure. Furthermore, no feed-back loop enabling a cybernetic relationship of those systems with bone is known. Instead of passively letting hormones regulate their "mass" in order to optimize their strength, bones would actively self-regulate their architecture following an anisotropic pattern in order to optimize their stiffness (the only known variable to be ever controlled in the skeleton) and strength "despite of" the endocrine systems. Three practical questions derive from those ideas: 1. Osteoporoses are not "intense osteopenias" but "osteopenic fragilities". 2. The diagnosis of osteopenia could be solved densitometrically; but that of bone fragility is a biomechanical problem which requires auxiliary resources for evaluating the stiffness and the spatial distribution of the mineralized material. 3. Osteopenias and osteoporoses should be on time evaluated as related to the mass or strength of the regional muscles, respectively, in order to differentiate between the "primary" (intrinsic lesion of the mechanostat) or "secondary" (systemic) etiologies and the biomechanical origin (disuse) in each case, with important therapeutic implications.

Postmenopausal changes in the distribution of the volumetric BMD of cortical bone. A pQCT study of the human leg.

Three different regions of interest (ROIs) were defined in pQCT scans (XCT-3000 machine, Stratec, Germany) taken at the tibial mid-diaphyses of 12 pre-menopausal (pre-MP) and 12 post-menopausal (post-MP) women who were otherwise normal, according to the volumetric bone mineral density (vBMD) value of their corresponding pixels (voxels) as assessed by their respective attenuation values. They were classified as "low-vBMD" (LD-ROI, with a vBMD of 200-400 mg/cm(3)), corresponding chiefly to trabecular-subcortical bone; "medium-vBMD" (MD-ROI, vBMD = 400-800 mg/cm(3)), corresponding mainly to porous cortical bone or cortical-subcortical bone, and "high-vBMD" (HD-ROI, vBMD higher than 800 mg/cm(3)), corresponding to dense cortical bone. The fraction of the total cross-sectional bone area covered by the HD-ROI was 16% higher, and that covered by the MD-ROI 20% lower, in pre-MP than post-MP women. No differences concerning the LDROIs were found. A close, linearly negative relationship was found between the MD- and HD-ROI fractions in all the women together, with no inter-group differences in slope. The Stress-Strain Index (an indicator of the torsional stiffness and strength of the whole bones that involved both the vBMD and the spatial disposition of the HD bone in the cross-section - torsional moment of inertia -) correlated linearly and positively with the cross-sectional area of the HD-ROI, with a higher slope for pre-MP than post-MP women. Qualitatively, a. post-MP women showed a significantly more prevalent discontinuity of the voxels in the HD-ROI than pre-MP women, and b. the tendency of LD-ROIs to accumulate along the mechanically lesseffective (antero-posterior) axis of the image - a characteristic of pre-MP bones - was visually less evident in post-MP bones. These features describe non-invasively some changes induced by menopause in the human tibia that may be critical for defining the skeletal condition and to monitor the effects of treatments addressed either to protect or to improve mechanically the bone structure, beyond the possibilities of standard densitometry.

Densitometric and tomographic analyses of musculoskeletal interactions in humans.

Previous studies with standard densitometry (DXA) have suggested that the bone mass is strongly dependent on the muscle mass in the species, following a similar relationship at any age and sex hormones or related factors potentiate that relationship. Studies with pQCT indicated that the surplus bone mass per unit of muscle mass previously observed in premenopausal women would be stored in skeletal regions with relatively little mechanical relevance, thus avoiding remotion through mechanically oriented remodelling by the bone mechanostat. Scanning the distal radius with pQCT has also showed a highly significant, linear relationship between SSI of the distal radius and the dynamometric maximal bending moment of the forearm in normal men and women. In order to investigate similar relationships in regions that are inaccessible to pQCT, we used spinal radiographs and axial QCT. This study affords additional evidence to the previous references concerning the direct, significant impact of the regional muscle strength on the determination of the tomographic indicators of bone mechanical quality and their indirect repercussion of the skeletal condition (curvature of the spine).

Olpadronate: a new amino-bisphosphonate for the treatment of medical osteopathies.

Olpadronate is a nitrogenated bisphosphonate. Although it shares the therapeutic and pharmacological properties of pamidronate and alendronate, it has a greater dosage amplitude, more predictable effects and a greater digestive tolerability than other bisphosphates. Therefore, it may be more appropriate in the treatment of medical osteopathies, by both oral and parenteral routes of administration. According to various experimental and human models, the pharmacological potency of olpadronate is 5- to 10-times higher than that of pamidronate and close to that of alendronate. The two methyl groups bound to the nitrogen atom give the compound a high water solubility, which is about 8-times higher than that of the two other bisphosphonates. The lack of a terminal amino group in the side-chain of the molecule and the absence of crystallised forms of the compound in the digestive tract (due to its high water solubility) may avoid the potential for inducing oesophageal and gastrointestinal side-effects. These features may explain the high tolerability reported after the administration of doses of olpadronate (by the oral route) up to 5- to 10-times higher than the maximum tolerated dose of alendronate in Paget's bone disease and bone metastases, thus widening the possibilities for its clinical usage. In addition, initial pharmacokinetic studies suggest that olpadronate's oral bioavailability would fit into a confidence range of 2-4%, which contrasts with the erratic absorption shown by other highly potent bisphosphonates. The clinical efficacy demonstrated in preliminary studies in Paget's bone disease (including ultra-short treatments), and also in single-dose iv. therapy of hypercalcaemia of malignancies, renders olpadronate among the most promising bisphosphonate compounds, with potential use in the treatment of a variety of bone-involving diseases, such as osteoporosis, malignancies and rheumatoid arthritis.

Site-dependent bone mineral density response to oral pamidronate and calcium in postmenopausal osteoporosis: a preliminary report.

Radiologically diagnosed postmenopausal osteoporotic patients with at least one nontraumatic vertebral flattening were treated for one year with either oral pamidronate (APD), 300 mg/day plus calcium 1 g/day (n=39) or with calcium alone (n=21). Bone mineral density (BMD) was assessed in lumbar spine, femoral neck, trochanter and Ward's triangle by dual X-ray absorptiometry in order to determine the number of responders at each site. As no densitometric inclusion criteria were stipulated, wide inter- and intra-individual variations in both regional basal BMD and response to therapy were found. However, the APD-treated group showed significant mean BMD increases in spine (+3.1%; p < 0.001) and femoral neck (+3.2%; p < 0.002) versus basal level, whereas the calcium only group failed to exhibit significant differences. The entire 60-strong population was then split into two groups, according to whether individual BMD content was greater or less than the mean basal value for each skeletal site evaluated. For either treatment, subpopulations with lower basal BMD tended to achieve greater bone gain, though statistically significant differences were only disclosed at trochanter (p < 0.004) with APD and at femoral neck (p < 0.002) in the calcium only group. Globally speaking, increases in BMD were observed in 60-80% of patients receiving either treatment - who were thus defined as responders - at each particular skeletal area assessed. However, when only skeletal areas with low basal BMD were considered, the number of responders reached 60-100%. Responsive sites varied among patients: out of 56 cases, 9 (24%) on APD and 6 (32%) on calcium alone responded in all 4 areas evaluated, while a single case on the latter treatment failed to show BMD response at any site. Overall, the mean number of responsive sites was 2.7. Odds ratios were calculated considering treatment modality and high or low basal BMD as parameters, but no significant differences were found in the number of responders. It may be concluded that APD induces moderate lumbar and femoral neck bone mass gain in severe postmenopausal osteoporosis, whereas calcium alone leads to non significant variations, both findings being in agreement with reported data. Therefore, evaluated APD doses enhance mineralization in responsive sites alone, but fail to increase the total number of responders. Interestingly, responsive sites seem to be those relitively spared by the course of the disease.

[Morphological studies of hydroxyapatite crystals exposed to disodium pamidronate]. / Estudios morfológicos de los cristales de hidroxiapatita tratados con pamidronato disódico.

"In vitro" effects of disodium pamidronate on hydroxyapatite crystals morphology, and some "in vivo" data from bone powder of tibia and vertebrae from treated young and mature rabbits are here reported. Hydroxyapatite, synthesized following Rigoli et al method, and bone powder from rabbits were studied with X-ray, infrared and raman emission techniques for crystallographic analysis. Adsorption studies were also performed with a balanced solution of hydroxyapatite exposed to different times, 48, 120 and 168 hours and concentrations 1 x 10(-5) M, 3 x 10(-5) M, 8 x 10(-5) M y 1 x 10(-4) M of pamidronate. Infrared and raman spectrometry were not conclusive due to technical bias, but X-ray difractograms showed pure hydroxyapatite crystals in an hexagonal system. At constant time, pamidronate concentrations were varied, showing after 48 hours of exposition, a slight growth in the 002 plane, an aleatoric behavior in 213 and a marked increase in 004. After 120 hours, 002 plane is steady with a net growth in 004 and 213. After 168 hours, the 3 mentioned planes grow in proportion to pamidronate concentrations, tending to enlarge the crystal shape. Plane 13 markedly grow with pamidronate 8 x 10(-5) M a 1 x 10(-4) M, which are biologically high concentrations. Potentiometric assessments, in the 1 x 10(-5) to 1 x 10(-4) M range of concentrations show that bisphosphonate was completely adsorbed to the crystals. Additional "in vivo" observations showed changes in bone powder crystals isolated from pamidronate treated young animals, involving a growing of planes 002 and 211, in samples from both epiphysis and diaphysis, regarding untreated samples. Changes were more evident at epiphysis. In mature rabbits, it was shown a decrease in basal plane 002 and growing at 210, 211 and 310 with a trend to enlarge the crystal shape in diaphysis and to shorten it in vertebrate spongiosa. The "in vivo" doses are equivalent to those used by Ferretti et al. in intact rats with pamidronate low dose groups, showing an improvement of bone material properties and stiffness. Thus, it may rather be lower than the "in vitro" used concentrations. In concordance with above experimental conditions it can be concluded that bisphosphonates exert morphological changes in hydroxyapatite crystals, in a dose dependent manner, at least when high concentrations are used. In addition, it is postulated that changes observed on "in vivo" samples may be the result with other adaptative factors as for example the local mechanical usage. The latter data were limited, and should be studied with more details if an extrapolation to the bisphosphonate treated osteoporotic women is intended. Finally, it is suggested that any agent that changes BMU activity (all known anti-osteoporotic drugs) may potentially modify the quality of hydroxyapatite crystals, affecting in turn the bone resistance to fracture, independently from the quantity of bone mass gained. Thus, to help predicting the consequences on skeletal fragility, there is a need to know the direct or indirect effect of drugs on bone crystals.

[Extended use, up to 6 years, of an oral amino-bisphosphonate in patients with established osteoporosis]. / Uso prolongado, hasta 6 años, de un amino-bisfosfonato oral en pacientes con osteoporosis establecida.

In osteoporotic women (n:163), 63.8 (+/- 8.1) years old and 15.2 (+/- 8.3) years since menopause, oral (200 mg/day) pamidronate was administered during protracted periods, up to 6 years. During the first 4 years of therapy significant increases from basal in both, lumbar spine and femoral neck were reported (p < 0.01). Patients who underwent to 5-6 years of treatment also showed positive results in both skeletal sites. Whole body mineral content estimated a 23.8 g/year mean gain during a 4-year period. Biochemical bone markers of resorption and formation reflected a variable degree of bone turnover decrease. Such changes were more pronounced at the beginning, and remained steady after the first year of continuous therapy. Calcemia remained between normal range without any hypocalcemic episode being reported. Phosphatemia, within normal range, showed a smooth trend to increase. PTH remained within normal range and vitamin D tended to slightly increase. The total number of new bone fractures and total number of patients with new fractures were less frequent during the pamidronate treatment period than before (p < 0.01). Indeed, the relative risk (RR) of fracture was estimated comparing the treatment lapse, 495 patient/year, vs a pretreatment period of 1,814 patient/year. Overall RR resulted less than 1 (RR = 0.83; CI 95% = 0.53-1.26). In total, hip, forearm and "other" fractures, RR was also less than 1 and remained over 1 in vertebral fractures. The latter can be explained because our sample started its treatment probably in a period of increased spine crushing. Overall fracture results, in a sample of patients as own controls and in spite of differences in ages, suggested that during treatment, patients improved their skeletal biomechanical competence, mainly in sites where cortical bone plays a meaningful role, as in femoral neck. It is concluded that pamidronate is an effective tool to ameliorate the skeletal conditions of postmenopausal osteoporotic women.

[Clinical application of bisphosphonate's pharmacokinetic principles]. / Aplicación clínica de los principios farmacocinéticos de los bisfosfonatos.

Bisphosphonates are a group of osteotropic substances able to modulate bone metabolism in different ways. They all display similar pharmacokinetic characteristics when administered in proportional dosages and assessed by similar methods. With the exception of olpadronate which is soluble in water, bisphosphonates have poor solubility, and may easily precipitate in the digestive media. In spite of their low digestive absorption (Bioavailability: 0.3-5%), they are effectively administered by oral route. Once in plasma they distribute rapidly, being uptaked by mineralized tissues, plasma proteins or eliminated by renal filtration in few minutes. The fraction retained in bones may be stored for long periods (from months up to 10 years depending on the compound) in an apparent inactive compartment. The risks of newly released molecules may be related to the potency of the drug. Within the clinical range of doses, bisphosphonates are not retained in soft tissues. This may explain the lack of extraskeletal collateral effects. Plasma blood levels are scarcely related to the clinical activity. Therefore, dosage may be guided better by biochemical markers of the bone disease than by the standard kinetic variables. On the other hand, dose is independent from age and/or body weight. Only renal impairment may induce additional dose adjustments.

[Tolerability of oral bisphosponates in patients with osteoporosis and other osteopathies]. / Tolerabilidad digestiva de los bisfosfonatos orales en pacientes con osteoporosis y otras osteopatías medicas.

Oral nitrogen containing bisphosphonates (NCB) are effective drugs to inhibit bone metabolism turnover in osteoporosis and other bone diseases. Notwithstanding, some digestive disturbances create concern on the long term acceptance of the oral route. Side effects are mainly caused by low absorption and poor solubility in digestive content. Therefore the compound may precipitate and irritate the mucosas. Furthermore, the administered amount of a particular molecule, its intrinsic potency to irritate digestive walls and the degree of exposition to such sensitive tissue are other facts that combined, may determine the clinical tolerability. Thus, a single factor cannot predict the clinical tolerability. Pamidronate, alendronate and olpadronate are the main NCB under clinical usage. Alendronate is 10 times more potent than pamidronate but possesses a similar slight solubility (2.4 vs 3.0% W/V respectively). It also seems to be more (3 times fold) ulcerogenic in experimental assays. The current available pamidronate formulation protects from esophagus and gastric exposition. Up to now and until randomized clinical trials be performed the selection of the most tolerated aminobisphosphonate in clinical practice will depend on the interplay of many factors (table 1 shows a hypothetical view). Moreover, different patients may react dissimilarly depending on their sensitivity to a particular factor. Olpadronate is free-soluble (24% W/V), almost equipotent with alendronate (figure 1) and seems to lack relevant irritation potential, but clinical data is on its early phases and is still not available. Micronization of the bisphosphonate preparation may be of help to improve tolerability as shown with newer pamidronate oral formulations. The current clinical published data shows more or less the same safety profile for pamidronate (only when enteric coated capsules are used) as alendronate, with more than 90% of patients complying with long term treatments. Anyway the trials are not entirely comparable as said before. Some other pamidronate formulations proved to be intolerable and have not been accepted. Identifying the many factors of oral NCB's digestive tolerability may help with their clinical management. And in those countries where the two compounds are available they may alternatively be used in the sensitive patients. Finally, extra-digestive side effects, not commented in this article, should also be weighted when selecting a bisphosphonate.

Mineral density gain in vertebrae of osteoporotic women on oral pamidronate reverts a year after treatment discontinuance.

Long-term treatment with 200 mg dry weight/day of pamidronate (APD) by oral route has been proposed to increase bone mineral density (BMD) in postmenopausal osteoporotic women. However, there is widespread concern over the possibility of bone metabolism "freezing" by protracted use of medication liable to inhibit bone resorption. Accordingly, an open population of 39 osteoporotic women was studied in order to determine BMD variations in lumbar vertebrae and femoral neck and to confirm whether given APD doses increase bone mineralization. A parallel group of osteoporotic women was likewise evaluated to determine the potential reversibility of such effect on discontinuing treatment. Results were beneficial at both skeletal sites in subjects on APD therapy, disclosing at 18 months treatment 9.0% mean peak mineral gain versus basal status at lumbar spine. In the few responders completing 4 years of treatment, mean differences versus basal status were +4.9% in vertebrae and +6.2% at femoral neck. In lumbar vertebrae there was a rapid trend in mineral gain up to 18 months on treatment, which declined thereafter to a quarter of its early rate. Concurrently, in the group of 21 baseline-matched women, effects were evaluated after discontinuing daily APD administration one year (n = 11) or two years (n = 7) later. In both subgroups, there was a loss in lumbar (-7.1% and -9.8% respectively; p<0.01) and femoral neck BMD (-2.2% and -4.2% respectively; p: n.s.) on performing measurement one year after APD withdrawal. Furthermore, after three years treatment and subsequent discontinuance, three patients presented bone loss in lumbar vertebrae and minimal changes at femoral neck one year after APD withdrawal. Therefore, APD induces moderate BMD gain which proves reversible on discontinuing therapy, so that it seems unlikely that this compound should "freeze" bone metabolism to a significant extent. However, the precise degree of such reversibility requires evaluation in larger series.

[Effect of low doses of oral pamidronate (APD) on the calcemia of osteopenic or osteoporotic patients]. / Efecto de bajas dosis del pamidronato (APD) oral sobre la calcemia de pacientes osteopenicas u osteoporoticas.

Oral pamidronate (APD) at high doses (400-900 mg/day) is employed as antiresorptive agent for the treatment of Paget's disease. In some occasions hypocalcemia may occur, and is interpreted as a relative overdosage. To avoid this complication and the consequent PTH release, supplementation with calcium salts is recommended. In osteoporotic syndromes, APD is prescribed at a lower dosage (200 mg/day) and currently calcium or vitamin D are also systematically added. But at this low dose the antiresorptive activity is partial and transient. In order to observe the effects on calcemia of multiple therapy, data from 129 postmenopausal women with the diagnosis of osteopenia or osteoporosis treated with 200 mg/day of APD soft capsules during 6-10 months, were gathered retrospectively. The first group (n: 13) received APD alone; the second group was supplemented with 1 g/day calcium salts (n: 61); the third group received 0.015-0.025 mg/day vitamina D (n: 10); and the fourth received both calcium plus vitamin D (n: 45). In samples of 24 h, urine, calcium, creatinine, hydroxyproline, and serum total calcium were measured before and after therapy. No hypocalcemia was detected. All groups, except the one treated with APD alone, showed a significant trend to increase their calcemia values between normal ranges (Table 1, 2). Only in one patient treated with APD + Ca + vitamin D, hypercalcemia was detected. Measuring HOP/Cr and Ca/Cr in urine as resorption markers, showed that 27% of the APD + Ca group and 33% of the APD + Ca + vitamin D group showed scant or any repercussion on mentioned resorption indexes, meaning that the response to APD could be hindered in those cases. In conclusion, while using low doses of oral APD, calcium salts should not be systematically recommended. There is no trend to hypocalcemia. Furthermore, calcium salts may favor drug interactions and so induce digestive side effects or poor responses. Calcium supplementation should be prescribed only on the basis of low calcium diet and not to prevent APD collateral effects on calcemia.

Serum kinetics, bioavailability and bone scanning of 99mTc-labelled sodium olpadronate in patients with different rates of bone turnover.

The activity of olpadronate labelled with technetium-99m(99mTc) was monitored in plasma and urine samples after single oral (925 MBq 99mTc/10 mg, coadministered with 50 mg cold drug) and intravenous (925 MBq 99mTc/5 mg) administrations to two groups of patients with different rates of bone turnover. The first group comprised high bone turnover (HBTO) patients suffering from Paget's bone disease; the second group comprised patients with normal to low bone turnover (NBTO) having the diagnosis of rheumatoid arthritis and secondary osteoporosis. Kinetic variables were correlated with anthropomorphometric variables, biological markers of bone metabolism and plasma proteins. Data were also obtained after repeatedly dosing the HBTO patients. Additionally, Paget's bone and healthy bone (PB/HB) uptake before and after low-dose oral treatment were assessed by means of scintigraphy. Results showed that most of the kinetic variables did not differ between the two groups of patients, except for a greater Vss and smaller blood area under the curve AUC in the patients with HBTO. After a repeated-dose administration period, the blood AUC activity and Whole Body Retention (WBR) of the HBTO patients tended to be similar to those of the NBTO patients. In both groups, after oral dosing, the Cmax was 20 times lower than the C0.5 after i.v. injection, and the oral bioavailability ranged from 3% to 4%. Finally, the plasma t1/2 beta ranged from 9 to 14 h. Correlation coefficients were obtained from multiple regression analysis; kinetic variables showed very low correlations with anthropomorphometric measurements. In contrast the Vss and WBR were significantly correlated with serum alkaline phosphatase levels and the Vss also with urine hydroxyproline levels. Plasma protein concentration was also correlated with excretion parameters such as CLP and plasma t1/2 beta after an oral dose. Scintigraphic studies in the HBTO group allowed bone selectivity to be seen through skeletal drug uptake. The 15 Pagetic lesions analysed in the HBTO group showed a decrease in PB/HB ratio from 3.8 in the basal study to 2.7 after olpadronate administration for 30 days at the rate of 50 mg/day. In conclusion, the kinetic profile of 99mTc-labelled olpadronate, mainly AUC and WBR, showed a dependence upon bone metabolism and seemed unrelated to body size variables. HBTO patients showed a lower blood AUC but a higher Vss. Both variables may have been reflecting the fact that the drug binds selectively with calcified tissues and, in turn, with the target compartment. Scintigraphy confirmed the labelled-compound bone selectivity as a desirable feature for a bone-scanning agent.