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

Analysis of bisphosphonate using ultraviolet-visible spectroscopy based on modified phosphorus determination reagent

An improved phosphorous determination was developed using ethanol, phosphorus determination reagent (PDR) and Ultraviolet-visible spectroscopy (UV-Vis) for analyzing the bisphosphonates (BPs). The method was carried out under mild conditions without digestion, high temperature, high pressure, and other extreme conditions. Alcohols played an important role in this method. Without alcohol, this reaction system did not have a color reaction. Alendronate (ALN) and risedronate (RIS) were used to demonstrate the reliability of the improved phosphorous determination under different reaction conditions. The absorbance had an equal ratio of increase as well as a good trend line when the content of BPs increased. The improved phosphorous determination could be a new method to measure the drug content of BPs.

Determination of Zoledronic Acid and Its Related Substances by High Performance Liquid Chromatography with Evaporative Light Scattering Detection

A method has been developed and validated for analysis of zoledronic acid (ZOL) and its related substances by ion-pair reversed-phase high performance liquid chromatography with evaporative light scattering detection (ELSD). Chromatographic separation was achieved with gradient elution by using a C18 column, mobile phase containing 12 mM ammonium acetate buffer and 35 mM n-pentylamine, whose pH value is 7.0, and 5% acetonitrile. The mobile-phase flow rate was 1.0 mL/min. The calibration plot was linear in the range from 0.4 mg/mL to 6.0 mg/mL for ZOL and from 6.25 μg/mL to 100 μg/mL for its related substances. ZOL and its related substances, namely imidazole-1-yl-acetic acid, phosphate, phosphite and degradation products did not interfere with each other. The method was rapid, linear, accurate and reproducible. The high performance liquid chromatographic method that has been developed to determine the related substances and assay of ZOL can be used simultaneously to evaluate the quality of regular samples. It can be also used to test the stability samples of ZOL.

UPLC-UV method for determination of risedronate in human urine

This study was designed to develop a sensitive and rapid method for the quantitation of risedronate in human urine using ultra-performance liquid chromatography with ultra-violet detector (UPLC-UV) and to compare bioavailability parameter of 5, 35 and 150 mg risedronate. The mobile phase consisted of sodium phosphate buffer, 1 mM etidronate-acetonitrile (95:5, v/v), pH 9.0, and was pumped at a flow rate of 0.3 mL/min. Detection of risedronate in human urine by the UPLC-UV was accurate and precise from 20 ng/mL to 5 μg/mL (a correlation coefficient of 0.99) with 97.16% in mean recovery. The intra-day accuracy was 89.17-110.43% with precision of 0.04-3.16% and the inter-day accuracy was 89.23-110.19% with precision of 1.63-9.72%. Aet (accumulated excretion amount) of risedronate in the urine after 5, 35 and 150 mg administration was 35.08, 246.67 and 1.413.85 μg within 36 h and Umax (maximal excretion rate) was 12.11, 77.7 and 374.24 μg/h, respectively. The assessed dose proportionality of Umax and Aet with three single doses of risedronate was found in an approximately linear manner. These results indicate that the developed simple, rapid and robust assay enables the complete processing of large samples for pharmacokinetic studies of risedronate in biological fluid.

Alendronate sodium

This chapter is a review on physical and chemical properties, methods of preparation, analysis, as well as pharmacodynamics and pharmacokinetics of Alendronate sodium (4-amino-1-hydroxybutane-1,1-diphosphonic acid sodium salt), a bone metabolism regulator, indicated for the treatment of excessive bone resorption and osteoporosis.

Bisphosphonate-based strategies for bone tissue engineering and orthopedic implants

Bisphosphonates (BPs) are a group of well-established drugs that are applied in the development of metabolic bone disorder-related therapies. There is increasing interest also in the application of BPs in the context of bone tissue engineering, which is the topic of this review, in which an extensive overview of published studies on the development and applications of BPs-based strategies for bone regeneration is provided with special focus on the rationale for the use of different BPs in three-dimensional (3D) bone tissue scaffolds. The different alternatives that are investigated to address the delivery and sustained release of these therapeutic drugs in the nearby tissues are comprehensively discussed, and the most significant published approaches on bisphosphonate-conjugated drugs in multifunctional 3D scaffolds as well as the role of BPs within coatings for the improved fixation of orthopedic implants are presented and critically evaluated. Finally, the authors' views regarding the remaining challenges in the fields and directions for future research efforts are highlighted.

Determination of zoledronic acid in human urine and blood plasma using liquid chromatography/electrospray mass spectrometry

A new method for the analysis of 1-hydroxy-2-imidazol-1-yl-phosphonoethyl phosphoric acid (zoledronic acid) in urine and blood samples has been developed. It consists of a derivatisation of the bisphosphonate with trimethylsilyl diazomethane under multiple methylester formation. The formed derivative can, in contrast to the non-derivatised analyte, easily be separated by reversed phase liquid chromatography due to its reduced polarity. Detection is performed by electrospray tandem mass spectrometry. For calibration purposes, a deuterated internal standard has been synthesised in a three-step synthesis starting with d(4)-imidazole. For human urine, the limit of detection (LOD) is 1.2x10(-7) mol/L, limit of quantification (LOQ) is 3.75×10(-7) mol/L in the MRM mode. For human blood plasma, a LOD of 1×10(-7) mol/L and a LOQ of 2.5×10(-7) mol/L were determined. The linear dynamic range comprised 3.5 decades starting at the limit of quantification. The method was successfully applied for the analysis of spiked urine and blood plasma samples as well as samples from two osteoporosis patients.

Review of operating principle and applications of the charged aerosol detector

Recently a new detection method, based upon aerosol charging (the charged aerosol detector (CAD)) has been introduced as an alternative to evaporative light-scattering detector (ELSD), chemiluminescent nitrogen detector and refractive index detector for detection of non-ultraviolet and weakly ultraviolet active compounds and for UV-absorbing compounds in the absence of standards. The content of this review article includes description of operation principle, advantages and disadvantages of CAD system, and short reports of selected applications of this detector. The main advantages of CAD detector are unique performance characteristics: better sensitivity than ELSD system, a dynamic range of up to 4 orders of magnitude, ease of use and constancy of response factors. Both detectors are mass dependent and the response generated does not depend on the spectral or physicochemical properties of the analyte. This attractive feature of a detection technique generating universal response factors is the potential use of a single, universal standard for calibration against which all other compounds or impurities can be qualified. CAD also has the same limitation as ELSD, namely, the response is affected by mobile-phase composition. This problem has been resolved by using inverse gradient compensation as is done for high pressure liquid chromatography and supercritical fluid chromatography. CAD has been applied for the analysis of structurally diverse compounds used in the pharmaceutical, chemical, food, and consumer products industries and in life science research. They include nonvolatile and semivolatile neutral, acidic, basic, and zwitterionic compounds, both polar and nonpolar (e.g. lipids, proteins, steroids, polymers, carbohydrates, peptides).

In vitro determination of the release of alendronic acid from alendronate tablets of different brands during deglutition

Alendronic acid, a frequently applied compound for the treatment of different forms of diseases of bone metabolism, is a strong acid with a high solubility in water. In connection with the oral administration this exhibits a potential health risk for the upper gastrointestinal tract. The in vitro release of tablets containing alendronic acid of different brands (Stada, ratiopharm, interpharm, Fosamax) was determined by dissolution tests for the time period required for oral intake. The effect of rotation speed, temperature, and solvent volume on the release rate of alendronic acid was determined for the used dissolution apparatus. Analysis of alendronic acid was performed by a validated HPLC method. The highest rate of release was found for the original brand. The dissolution rate of the generic formulations was significantly lower in the early stage of dissolution. Over the complete range of dissolution, more than 85% of the claimed amount was dissolved within 4 min. Dissolution profiles were compared by calculation of the similarity factor f(2) showing equal products with the exception of one generic product, whose dissolution rate was lower.

Complexation of bisphosphonates with ytterbium(III): application of phosphate and ATP detection assay based on Yb(3+)-pyrocatechol violet

The coordination chemistry of bisphosphonates with Yb(3+) was investigated to evaluate the potential of the UV-vis based detection method using the Yb(3+)-pyrocatechol complexation reaction as a sensor for bisphosphonates. The complexation chemistry of Yb(3+) with phosphate and ATP analogs was previously described (E. Gaidamauskas, K. Saejueng, A.A. Holder, S. Bharuah, B.A. Kashemirov, D.C. Crans, C.E. McKenna, J. Biol. Inorg. Chem. 13 (2008) 1291-1299), and we here studied the complexation chemistry of bisphosphonates in this system. The spectrophotometric assay yields direct evidence for formation of a 4:3 metal to ligand complex at neutral pH. Direct evidence for Yb(3+):methylenebis(phosphonate) complexes with 1:1 and 1:2 stoichiometry was also obtained by potentiometry at acidic and basic pH. Direct evidence for complex formation was obtained using (1)H NMR spectroscopy although the stoichiometry was not accessed at neutral pH. Our results suggest that the spectroscopic observation of the YbPV complex can be used to conveniently measure concentrations of bisphosphonates down to 2-3 microM.

Metal complexation chemistry used for phosphate and nucleotide determination: an investigation of the Yb3+-pyrocatechol violet sensor

Metal complexation reactions can be used effectively as sensors to measure concentrations of phosphate and phosphate analogs. Recently, a method was described for the detection of phosphate or ATP in aqueous solution based on the displacement by these ligands of pyrocatechol violet (PV) from a putative 2:1 (Yb3+)2PV complex. We have not been able to reproduce this stoichiometry and report this work in order to correct the coordination chemistry upon which sensor applications are based. In our work, colorimetric and spectrophotometric detection of phosphate was confirmed qualitatively (blue PV+Yb3+; yellow+Pi); however, the sequence of visual changes on the titration of PV with 2 equiv. of Yb3+ and back titration with ATP as described previously could not be reproduced. In contrast to the linear response to Pi that was reported previously, the absorbance response at 443 or 623 nm was found to be sigmoidal using the recommended 2:1 Yb3+:PV solution (100 microM:50 microM, pH 7, HEPES). Furthermore, both continuous variation titration and molar ratio analysis (Job plot) experiments are consistent with 1:1, not 2:1, YbPV complex stoichiometry at pH 7 in HEPES buffer, indicating that the deviation from linearity is produced by excess Yb3+. Indeed, using a 1:1 Yb3+:PV ratio produces a linear response in DeltaAbs at 443 or 623 nm on back titration with analyte (phosphate or ATP). In addition, speciation analysis of the Yb-ATP system demonstrates that a 1:1 complex containing Yb3+ and ATP predominates in solution at microM metal ion and ATP concentrations. Paramagnetic 1H NMR spectroscopy directly establishes the formation of Yb3+-solute complexes in dilute aqueous solution. The 1:1 YbPV complex can be used for the colorimetric measurement of phosphate and ATP concentrations from approximately 2 microM.

Determination of bisphosphonate active pharmaceutical ingredients in pharmaceuticals and biological material: a review of analytical methods

Bisphosphonates is a class of chemical compounds finding extensive medical applications against bone disorders including osteoporosis, Pagets' disease, etc. Non-N-containing members include etidronate, clodronate and tiludronate, while N-containing bisphosphonates include active pharmaceutical compounds such as pamidronate, neridronate, olpadronate, alendronate, ibandronate, risedronate and zoledronate. The present study covers 20 years of analytical research on this group of compounds, focusing on bioanalytical and pharmaceutical QC applications. A wide range of analytical techniques is presented and critically discussed including among others liquid and gas phase separations, electrophoretic, electroanalytical, automated and enzymatic approaches.

Simple analysis of four bisphosphonates simultaneously by reverse phase liquid chromatography using n-amylamine as volatile ion-pairing agent

Volatile organic amine was used as the mobile phase addictive during the separation of four bisphosphonates (alendronate, pamidronate, zoledronic acid and etidronate). An isocratic liquid chromatography method with evaporative light-scattering detection (ELSD) was developed for these bisphosphonates which are not retained on non-polar column and lack chromophore for detection. The analytes have sufficiently separated from each other on a Phenomenex C18 column. The effects of mobile phase composition and instrumental parameters of ELSD were studied. This newly developed method enables direct measurement for analysis of bisphosphonates without the need of derivatization. This developed method provides high separation and specificity to bisphosphonate analysis. In quantitative analysis, the method showed satisfactory precision (less than 2.8%) and accuracy (higher than 94.4%), good linearity (r=0.9991-0.9997) and sufficient sensitivity (15-18 microg/ml). It can be easily and conveniently adopted for the routine quality control analysis.

High-performance liquid chromatography method for determining alendronate sodium in human plasma by detecting fluorescence: Application to a pharmacokinetic study in humans

A high-performance liquid chromatographic (HPLC) method was developed using diethylamine (DEA) solid-phase extraction (SPE), 9-fluorenylmethyl derivative (FMOC) and fluorescence detection for quantifying alendronate in human plasma. Sample preparation involved a manual protein precipitation with trichloroacetic acid, a manual coprecipitation of the bisphosphonate with calcium phosphate and derivatization with 9-fluorenylmethyl chloroformate in citrate buffer at pH 11.9. Liquid chromatography was performed on a Capcell Pak C(18) column (4.6 mm x 150 mm, 5 microm particles), using a gradient method starting with mobile phase acetonitrile/methanol-citrate/pyrophosphate buffer (32:68, v/v). The total run time was 25 min. The fluorometric detector was operated at 260 nm (excitation) and 310 nm (emission). Pamidronate was used as the internal standard. The limit of quantification was 1 ng/ml using 3 ml of plasma. The intra- and inter-day precision expressed as the relative standard deviation was less than 15%. The assay was applied to the analysis of samples from a pharmacokinetic study. Following the oral administration of 70 mg of alendronate sodium to volunteers, the maximum plasma concentration (C(max)) and elimination half-life were 40.94 +/- 19.60 ng/ml and 1.67 +/- 0.50 h, respectively. The method was demonstrated to be highly feasible and reproducible for pharmacokinetic studies including bioequivalence test of alendronate sodium in humans.

Determination of bisphosphonates by ion chromatography–inductively coupled plasma mass spectrometry

An ion chromatography-inductively coupled plasma mass spectrometry (IC-ICP-MS) was introduced in the analysis of bisphosphonates. Two compounds (alendronic acid and etidronic acid) were separated on a Dionex AS-7 anion-exchange column with dilute nitric acid employed as the mobile phase. The analytes were detected at m/z 31, as they contain phosphorus. The detection limits achieved were 0.20 mg l(-1) for alendronic acid and 0.05 mg l(-1) for etidronic acid. Since the determination of phosphorus by ICP-MS is difficult due to polyatomic interferences at m/z 31 (15N16O+, 14N16O1H+, and 12C1H(3)16O+), a detailed study of the influence of plasma parameters on phosphorus and background signal was performed.

Determination of risedronate in human urine by column-switching ion-pair high-performance liquid chromatography with ultraviolet detection

An HPLC assay for the determination of risedronate in human urine was developed and validated. Risedronate and the internal standard were isolated from 5-ml urine samples in a two-part procedure. First, the analytes were precipitated from urine along with endogenous phosphates as calcium salts by the addition of CaCl(2) at alkaline pH. The precipitate was then dissolved in 0.05 M ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid and subjected to ion-pair solid-phase extraction using a Waters HLB cartridge (1 ml, 30 mg) with 1-octyltriethylammonium phosphate as the ion-pair reagent. Following extraction, the analytes were initially separated from the majority of co-extracted endogenous components on a Waters X-Terra RP18 (4.6 x 50 mm, 3.5 microm) column. The effluent from the X-Terra was "heart-cut" onto a Phenomenex Synergi Polar RP (4.6 x 150 mm, 4 microm) column for final separation. UV detection (lambda=262 nm) was used to quantitate risedronate in the concentration range of 7.5-250 ng/ml. Mean recovery was 83.3% for risedronate and 86.5% for the internal standard. The intra-day precision of the assay, as assessed by replicate (n=5) standard curves, was better than 6% RSD for all points on the standard curve. Within-day accuracy for the standards ranged from 96.3 to 106.1% of nominal. Inter-day precision for quality controls assayed over a 3-week period was better than 5%, while inter-day accuracy was within 90% of nominal. The assay was employed to analyze samples collected during a clinical pharmacokinetics study.

Determination of alendronate in human urine as 9-fluorenylmethyl derivative by high-performance liquid chromatography

A high-performance liquid chromatographic method for the quantitation of alendronate as the 9-fluorenylmethyl derivative (FMOC) in human urine is presented. The sample preparation involved coprecipitation with calcium phosphate, separation on diethylamine (DEA) solid-phase extraction (SPE) cartridge and derivatization with 9-fluorenylmethyl chloroformate in citrate buffer pH 11.9. Liquid chromatography was performed on an octadecylsilica column (150 x 4.6 mm, 3 microm particles); a gradient method with starting mobile phase acetonitrile-methanol-citrate/pyrophosphate buffer (20:15:65 v/v) was employed. The total run time was 21 min. The fluorimetric detector was operated at the following wavelengths: 260 nm (excitation) and 310 nm (emission). Pamdronate was used as the internal standard. The limit of quantitation was 3.5 ng/ml using 5 ml of urine. Within-day and between-day precision expressed by relative standard deviation was less than 8% and inaccuracy did not exceed 9%. The assay was applied to the analysis of samples from a pharmacokinetic study.

Ion exchange chromatographic determination of olpadronate, phosphate, phosphite, chloride and methanesulfonic acid

A method based on single column ion chromatography with UV detection was developed for purity testing and assay of monosodium olpadronate. The analyte aqueous solution is precipitated with methanol to enhance the impurities/olpadronate molar ratio, thus improving purity determination at trace levels. The resulting solution is injected into a standard chromatographic system with UV detector in indirect mode with a Waters IC Pak HR column using diluted nitric acid as the mobile phase. The method was fully validated according to ICH guidelines for the determination of phosphite, phosphate, chloride and methanesulfonic acid in olpadronate being suitable for purity testing and assay.

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.

Anion-exchange separation and determination of bisphosphonates and related analytes by post-column indirect fluorescence detection

Bisphosphonic acids and their salts can be detected after their liquid chromatographic separation by post-column indirect fluorescence detection (IFD). After separation the analyte is combined with the highly fluorescent Al(3+)-morin (2',3,4',5,7-pentahydroxyflavone) solution and fluorescence decreases because of the formation of the nonfluorescent Al(3+)-bisphosphonate complex. The decrease in fluorescence is proportional to the amount of bisphosphonate present. Separation of the multivalent anionic bisphosphonate analytes from other anions and sample matrix is achieved on a strong base anion-exchange column with a strong, basic eluent. The post-column reaction variables, which influence IFD, are identified and optimized for the detection of the bisphosphonates after separation on the anion exchanger. The method is selective, since only a few anions will undergo a reaction with the Al(3+)-morin solution, and sensitive, detection limit for difluoromethylene bisphosphonate, F2MDP, is 4 ng for S/N = 3. The separation-IFD method can be applied to the determination of bisphosphonates, such as F2MDP, ethane-1-hydroxy-1,1-bisphosphonic acid, dichloromethylene bisphosphonic acid, 4-amino-1-hydroxybutane-1,1-bisphosphonic acid, in biological samples. The separation-IFD method is also applicable to the detection of inositol phosphate anions.

Chromatographic analysis of bisphosphonates

Chromatographic analysis of bisphosphonates in the past has been based primarily on reversed-phase liquid chromatography (RPLC) and ion-exchange chromatography. Gas chromatography (GC) and recently even capillary electrophoresis have also been employed. For bioanalysis, pre-treatment of the sample is a major part of the analysis; protein precipitation, calcium precipitation, solid-phase extraction (SPE) and derivatization have demonstrated to play an important role in bisphosphonate assays. For some of these treatments, for example SPE and derivatization, automation may be possible. Derivatization is a prerequisite for GC analysis of bisphosphonates; a volatile derivative has to be formed. For liquid chromatography, two types of derivatization are known for bisphosphonates. First, the bisphosphonate side chain can be modified by a chemical reaction to yield a derivative with advantageous chromatographic and spectroscopic properties. Secondly, by complexation of both phosphonate groups or of phosphate after decomposition of the analyte, a coloured complex can be formed. The most sensitive bioanalytical methods are based on RPLC and fluorescence detection, if necessary after derivatization. If low detection limits are not required, for example for analysis of pharmaceutical preparations, non-specific detection methods can be applied.

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.

The determination of pamidronate in pharmaceutical preparations by ion-pair liquid chromatography after derivatization with phenylisothiocyanate

An analytical method was developed for the determination of pamidronate [(3-amino-1-hydroxypropylidene)bisphosphonate] by ion-pair liquid chromatography. The analyte was derivatized with phenylisothiocyanate into an UV-absorbing derivative. The reaction product was cleaned-up by a double ion-pair extraction and treated with hydrogen peroxide prior to injection. Both, the detection limit and the lower limit of quantification of pamidronate in water were 0.1 microgram ml-1 disodium pamidronate. The intra-day precision was 3% for a 5-microgram ml-1 pamidronate standard solution and the inter-day precision 6% for a 3-microgram ml-1 solution. The method was applied in the quality control of pamidronate injection concentrates and tablets.

Determination of pamidronate in urine by ion-pair liquid chromatography after derivatization with 1-naphthylisothiocyanate

A sensitive method for the determination of pamidronate disodium [(3-amino-1-hydroxypropylidene)bisphosphonate, APD] in urine has been developed and validated. The procedure involves a triple co-precipitation with calcium phosphate, solid-phase extraction on a quaternary ammonium column, derivatization with 1-naphthylisothiocyanate and ion-pair liquid-liquid extraction. From the two reaction products, naphthylthiocarbamyl-APD is converted into the other, naphthylcarbamyl-APD, by an oxidative desulphuration with hydrogen-peroxide prior to analysis by ion-pair HPLC and fluorescence detection at 285/390 nm. The method has a coefficient of variation of 7% for the intra-assay precision of 99 ng ml-1 APD and 11% for the inter-assay precision. The lower limit of quantification is 3 ng ml-1 APD in 2.5 ml of human urine.

Pamidronate content and turnover in sternum, vertebral body, and iliac bones of dogs

Therapeutic efficacy of bisphosphonates depends on how much drug is present in bone. Therefore, it is important to measure the amount of bone bisphosphonate in toxicological and pharmacological studies. We analyzed pamidronate content of bone samples from two previously published long-term dose studies. In the first study, mature beagle dogs were given oral pamidronate at doses of 0, 2.5, 12.5 and 25 mg/kg per day for 1 year. The dogs in the second study received the same dosages for 1 year followed by 1 year without drug. In both studies, the amount of pamidronate measured was dependent upon dose in bone samples of ilium, sternum, and vertebral body. After 1 year of treatment, vertebral bone had more pamidronate than sternum or iliac bone on a permilligram basis. After 2 years, there was significantly less pamidronate in the vertebral body, sternum, and ilium than there had been at 1 year. The fall in pamidronate content was largest in vertebral body and least in the ilium. The higher uptake of pamidronate by the vertebral body during the 1 year study, and its greater loss of pamidronate after a year without drug treatment, would reflect the higher turnover of trabecular bone in the vertebral body vs. cortical bone in the ilium. The percent difference in bone pamidronate content between the 1 and 2 year dogs varied with dose. The largest percent loss occurred in the intermediate-dose group. These data suggest that, after 1 year without the drug, bone turnover rates in dogs treated with the highest dose of pamidronate were lower than at the intermediate dose. Thus, the time required for bone turnover rates to return to pretreatment levels is probably dose-dependent.

Extraction and measurement of pamidronate from bone samples using automated pre-column derivatization, high-performance liquid chromatography and fluorescence detection

A method for the determination of 3-amino-1-hydroxylpropylidene-1, 1-bisphosphonic acid (pamidronate) in bone samples is described. This method combines and modifies parts of previous procedures. Pamidronate is extracted from finely ground bone with dilute hydrochloric acid. Amine-containing contaminants are removed by co-precipitation of pamidronate with calcium. Excess calcium is removed with EDTA and an ion-exchange resin. Pamidronate is automatically derivatized at the primary amine and quantified by high-performance liquid chromatography with fluorescence detection. The method assay was linear in the concentration range 7.5-600 ng/mg bone (20-100 pmol/mg). The imprecision for repeat analyses were 16.5 and 7.8%, at pamidronate levels of 7.5 and 600 ng/mg bone, respectively. The method has been used to analyze bone samples from pharmacokinetic animal studies involving both acute and chronic dosages.

Determination of a glycine/NMDA receptor antagonist in human plasma and urine using column-switching high-performance liquid chromatography with ultraviolet, fluorescence and tandem mass spectrometric detection

High-performance liquid chromatography (HPLC) assays using ultraviolet (UV) and fluorescence (FL) detection were developed and compared with a liquid chromatography/tandem mass spectrometry (LC/MS-MS) method for determination of the glycine receptor antagonist 7-chloro-4-hydroxy-3-(3-phenoxy)phenyl-2(1H)-quinolone (L-701, 324, I) in human plasma and urine. The drug and internal standard (II) were isolated from the biological matrix through liquid-liquid extraction. In the HPLC-UV and HPLC-FL methods, the samples were initially injected onto a Cyano BDS Hypersil column, and the chromatographic region containing the peaks of interest was heart-cut onto an analytical C-18 BDS Hypersil column via a column-switching device. The analyte was quantified by monitoring either absorbance at 226 nm or fluorescence at 385 nm following 230 nm excitation. The limit of quantitation for I extracted from 1 ml of plasma or urine was 5 ng ml-1, and the assays were validated in the concentrated range of 5-200 ng ml-1. The LC/MS-MS method also utilized a column-switching protocol and was validated in the concentration range of 1-200 ng ml-1. Both assays provided data with precision and accuracy within less than 10% for all points in the standard curve range.

Rationale for the use of alendronate in osteoporosis

Bisphosphonates are being used in disorders associated with accelerated resorption of bone, particularly Paget's disease of bone and the bone disease of malignancy. Their undoubted biological efficacy and relatively low apparent toxicity make them attractive candidates for the management of osteoporosis. The bisphosphonate alendronate has many characteristics which suggest that it is suitable for use in osteoporosis. It is a potent inhibitor of osteoclast-mediated bone resorption with no adverse effect on the mineralization of bone. Earlier studies have shown it to be one of the most active bisphosphonates in Paget's disease and the hypercalcemia of malignancy. In common with other bisphosphonates tested thus far, alendronate appears to inhibit bone loss in a variety of experimental models of osteoporosis. Long-term studies are needed to determine its steady-state effects on bone mass in man. Most data indicate that alendronate is capable at least of decreasing the rate of bone loss, and might even induce increments in bone mass for many years. Since the experimental studies show that the increase in bone mass observed with alendronate is associated with an increase in bone strength, its use is likely to decrease the frequency of fractures. However, direct clinical evidence for this requires the outcome of well-designed long-term prospective studies.

Determination of bisphosphonate drugs in pharmaceutical dosage formulations by ion chromatography with indirect UV detection

Application of ion chromatography (IC) to the analysis of non-chromophoric bisphosphonate drugs in pharmaceutical dosage formulations is described. The method is based on the use of single-column ion chromatography in conjunction with indirect UV detection that obviates the need for tedious chemical derivatization procedures. Diluted drug samples are chromatographed directly on a Waters IC-Pak HR anion-exchange column with dilute nitric acid (1.6-12 mM) as the mobile phase which exhibits a UV absorption maximum near 220 nm. Analyte detection is monitored by measuring the decrease in absorption of the mobile phase. The IC method has been validated and shown to be precise, accurate, specific and rugged for routine assay. Application of the method to the determination of alendronate sodium tablets, etidronate disodium injectable (which requires an eluent pH control for chromatographic resolution of active drug from chloride ions) and clodronate disodium injectable is presented. The performances of the Waters IC-Pak HR and several equivalent columns are also discussed.

Ion-exchange liquid chromatographic analysis of bisphosphonates in pharmaceutical preparations

A simple, fast and uniform method has been developed for the quantitative determination of bisphosphonates in the quality control of pharmaceutical preparations. The method is based on ion-exchange liquid chromatography with conductivity detection. Separation is performed on a Waters IC-PAK Anion column using 2 mM nitric acid or 25 mM succinic acid as the mobile phase. Retention of the bisphosphonates can be influenced by pH and the anion concentration of the mobile phase. Sensitivity and selectivity are sufficient for the assay of bisphosphonates in bulk drug and pharmaceutical preparations. Sample preparation comprises dissolution or dilution of the sample in the mobile phase followed, if necessary, by filtration prior to HPLC analysis. Since the method is stability indicating, it is also well suited for shelf-life studies of bisphosphonate pharmaceutical preparations. Validation of the analytical method for the assay of pamidronate injection indicated an intra-day reproducibility of 1.7% (n = 6) and an inter-day reproducibility of 2.7% (n = 6). A linear relationship between response and concentration was found in the concentration range studied from 200 ng to 10 micrograms pamidronate per 20 microliters injected. The lower limit of detection (signal-to-noise ratio = 3) of pamidronate was about 100 ng.

Clinical pharmacology of alendronate sodium

Clinical studies have been performed to investigate the pharmacokinetics and pharmacodynamics of alendronate, an inhibitor of bone resorption for the treatment of osteoporosis. Alendronate is one of the most potent bisphosphonates currently undergoing clinical investigation (> 100-fold more potent than etidronate in vivo). The pharmacokinetics of alendronate are similar to those of other bisphosphonates. After a 2-h intravenous infusion, plasma concentrations of alendronate decline rapidly to approximately 5% of initial values within 6 h. About 50% of a systemic dose is excreted unchanged in the urine in the 72 h following administration. By analogy to its behavior in animals the remainder is assumed to be taken up by the skeleton. After sequestration into bone, the elimination of alendronate is very prolonged. The terminal half-life was estimated to be greater than 10 years. Despite prolonged skeletal residence, the biological effects of alendronate begin to diminish post-treatment, since the duration of effect reflects factors besides dose and cumulative drug exposure. When taken after an overnight fast, 2 h before breakfast, the oral bioavailability of alendronate averages approximately 0.75% of dose with substantial variability (coefficient of variation 55%-75%) both between and within subjects. Reducing the wait before food from 2 h to 1 h, or even 30 min, produces a mean reduction in absorption of 40%. Since the clinical efficacy of alendronate is indistinguishable whether it is given 30 min, 1h, or 3 h before a meal, the observed variability in bioavailability within this range is of little consequence. Dosing up to at least 2 h after a meal dramatically reduces absorption (80%-90%).

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.

Determination of a cyclic heptapeptide, a novel fibrinogen receptor antagonist, in human plasma by high-performance liquid chromatography with automated pre-column derivatization, column switching and fluorescence detection

A sensitive high-performance liquid chromatographic (HPLC) assay for the determination of the cyclic heptapeptide Ac-Cs-Asn-Dtc-Amf-Gly-Asp-Cys-OH (Dtc = beta,beta-dimethylthioproline, Amf = p-aminomethylphenylalanine) in human plasma has been developed. The key steps in the assay include: solid-phase extraction of the drug from plasma, chemical derivatization of the primary amino group with naphthalene-2,3-dicarboxyaldehyde in the presence of N-acetyl-D-penicillamine as a nucleophile to form a fluorescent benzo[f]isoindole derivative, and HPLC with column switching to provide the necessary chromatographic separation of the derivative from endogenous plasma components. The assay has been validated in the concentration range 1-10 ng/ml of plasma.

Determination of alendronate in pharmaceutical dosage formulations by ion chromatography with conductivity detection

A method was developed and validated for the direct determination in pharmaceutical dosage formulations of alendronate, a non-chromophoric compound. It is based on the use of single-column ion chromatography with conductivity detection that obviates the need for the tedious chemical derivatization procedures that are required for UV and fluorescence detection. Diluted samples of 0.05 mg/ml were chromatographed directly on a Waters IC-Pak HR anion-exchange column or a Dionex OmniPac PAX-100 column with dilute nitric acid as the mobile phase followed by conductivity detection. The method was validated and shown to be precise, accurate and specific for the assay of alendronate in intravenous (i.v.) solution and tablet formulations. The ruggedness of the assay was studied by generating data from four different instruments. Also established was the equivalence between this method and a previously reported high-performance liquid chromatographic method with 9-fluorenylmethyl chloroformate derivatization and UV detection. Application of the method to the determination of alendronate in i.v. and tablet formulations is presented and the performances of the Waters IC-Pak HR and Dionex OmniPac columns are discussed.