Development and application of a high-performance liquid chromatography-mass spectrometry method to determine alendronate in human urine.

Despite the high potential offered by electrospray ionization on highly polar compounds like biphosphonates, few applications have been developed. High-performance liquid chromatography (HPLC) separation methods suitable for such molecules cannot be used in tandem with mass spectrometry (MS) due to high non-volatile salt content; at the same time the sample preparation, in biological fluids, is also a challenging problem. In the past ion-pair chromatography was mainly used in the case of HPLC-MS of biphosphonates, but no application to quantitative pharmacokinetic (PK) studies has been presented. In this study, after preliminary tests with ion-pair chromatography showing a poor sensitivity, a combined derivatization of the amino group and the biphosphonate has been developed and tested in a PK study. Using this analytical approach we were able to fully validate the quantitation of alendronate in the range of 6.667-4860.0 ng/ml in urine (sample volume 2.0 ml); each analytical run was 5.0 min long. The sensitivity achieved permitted a correct evaluation of the alendronate urinary excretion over the full period of urine collection. Sample preparation despite its complexity permitted to process and analyze up to 200 samples in a working day.

Determination of disodium clodronate in human plasma and urine using gas-chromatography-nitrogen-phosphorous detections: validation and application in pharmacokinetic study.

We present a specific method for the determination of disodium clodronate in human plasma and urine using a gas-chromatographic system with nitrogen phosphorus detector (NPD). The compound was extracted from plasma and urine samples by an anion-exchange resin and derivatizated with bistrimethylsilyltrifluoroacetamide (BSTFA). Sodium bromobisphosphonate was used as internal standard. The calibration curves were linear in both plasma and urine, with a regression coefficient r > 0.9975 in plasma and r > 0.9977 in urine. The limit of quantitation was 0.3 microg/ml in plasma and 0.5 microg/ml in urine. The method was validated by intra-day assays at three concentration levels. During the study we carried out inter-day assays to confirm the feasibility of the method. The precision in plasma at 0.5, 15, and 45 microg/ml was 12.4, 0.2, and 6.5% (n = 40), respectively; in urine at 0.8, 8, and 40 microg/ml it was 8.6, 6.4, and 9.3% (n = 40), respectively. The method was accurate and reproducible, and was successfully applied to determine the pharmacokinetic parameters of clodronate in healthy volunteers after intravenous infusion and intramuscular injection of 200 mg of the compound. The Cmax after intravenous infusion and intramuscular injection was 16.1 and 12.8 microg/ml, respectively. AUC(0-48 h) after infusion administration and intramuscular injection was 44.2 +/- 18.0 and 47.5 +/- 12.4 h microg/ml, respectively. The elimination half-life in both administrations was 6.31 +/- 2.7 h.

Oral clodronate in breast cancer patients with bone metastases: a randomized study.

OBJECTIVES: To investigate the effect of the bisphosphonate clodronate on the occurrence of skeletal events (hypercalcaemia, fractures and radiotherapy) in breast cancer patients with bone metastases. DESIGN: Prospective, randomized, controlled, clinical trial. SETTING: A department of oncology in a university hospital. SUBJECTS: One hundred patients who received firstline systemic antineoplastic treatment for metastatic breast cancer with bone involvement were randomized to receive clodronate as two 400 mg capsules twice a day for 2 years or no additional therapy. RESULTS: In the clodronate group the number of skeletal events was reduced to 14 events in 48 evaluable patients as compared with 21 events in 51 evaluable control patients. The time to the first skeletal event was significantly longer in the clodronate group than in the control group (P = 0.015) and the most distinct difference was a lower occurrence of fractures in the clodronate group (P = 0.023). After 15 months the effect of clodronate tended to decline as the need for radiotherapy increased in the clodronate group compared with the control group (P = 0.069). Significant improvements in several quality-of-life aspects were seen in both groups during the first 6 months, but there was no significant difference between the groups. No effect was observed on time to radiologically evaluated disease progression in bone or on survival. The most frequent side-effects resulting in discontinuation of clodronate were nausea and diarrhoea. CONCLUSION: Oral clodronate is associated with a temporary reduction of morbidity related to bone metastases in breast cancer patients.

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.

Pooling of clodronate urinary excretion data: a new pharmacokinetic method to study drugs with highly variable gastrointestinal absorption.

Gastrointestinal absorption of bisphosphonates is highly variable from individual to individual (between-subject variation) and from day to day (within-subject variation), a fact that creates problems both in research and in clinical use of these drugs. We conducted a randomized, two-period cross-over pharmacokinetic (phase I) study to assess the relative bioavailability of two different clodronate preparations: an 800 mg tablet and a 400 mg capsule. Urinary excretion of clodronate correlates with gastrointestinal absorption. To minimize the confounding effect of the high variability of gastrointestinal absorption, we chose as the primary parameter the cumulative amount of clodronate excreted into urine (A(e0-t)) during 9 days (7 days of treatment, 2 days of follow-up). The 90% confidence interval calculated for the population medians of A(e0-t) was 0.83-1.09, well within the 90% confidence interval stipulated for bioequivalence for the area under the curve values (0.80-1.25). This new procedure for pooling urinary excretion data offered a clear advantage over previous methods, and thus could presumably be used to study other drugs as well that are not metabolized and may show highly variable gastrointestinal absorption.

Effect of concomitant administration of clodronate and estramustine phosphate on their bioavailability in patients with metastasized prostate cancer.

Estramustine phosphate is generally used as a second-line treatment in patients with advanced prostate cancer. The bone metastases due to the cancer are often treated simultaneously with clodronate in order to relieve the bone pain. Therefore, the interaction of clodronate (800 mg orally four times daily) and estramustine phosphate (280 mg orally twice daily) on their bioavailability was studied in twelve patients with prostate carcinoma and bone metastases. The drugs were first given separately, each to six patients, for five days, and then concomitantly for the same period. The bioavailabilities of the drugs were calculated on the last day of each treatment period. When clodronate was given alone, its concentrations in serum and AUC for one dose interval (6 hr) did not differ from those obtained with the drug given concomitantly with estramustine phosphate, nor did the combination of estramustine phosphate change the excretion of clodronate in urine. The serum concentrations of estramustine phosphate were elevated by about 80% when the drug was given together with clodronate. The AUC for one dose interval (12 hr) was also significantly higher for estramustine phosphate with clodronate than without clodronate. The urinary excretion of estrone, a major metabolite of estramustine phosphate, was also significantly higher after the admission with clodronate. The results suggest that clodronate increases the oral bioavailability of estramustine phosphate.

Pharmacokinetics of clodronate in renal failure.

The pharmacokinetic parameters describing the fate of one intravenous clodronate (disodium dichloromethane diphosphonate) dose was studied in 24 normal subjects and in 24 patients with different degrees of renal insufficiency. The aim of the study was to derive data for adjustment of dosage in relation to renal function. Disodium clodronate in serum and urine samples was analyzed by capillary gas chromatography with mass-selective detection. The renal clearance (CLR) of clodronate was highly dependent on renal function and declined successively with declining glomerular filtration rate (GFR). Plasma clearance (CLP) declined, too, but to a lesser degree than CLR. The impairment of renal function resulted in decreased cumulative urinary elimination of clodronate and increased total areas under the serum concentration-time curve (AUC0-infinity). Hence, as the renal elimination of clodronate diminishes with decreasing GFR, there is a related retention of the substance. As a result of the present study, the following dosages are recommended: creatinine clearance (CLCr) from 50 to 80 ml/minute, 75-100% of normal dose; CLCr 12-50 ml/minute, 50-75% of normal dose; and ClCr < 12 ml/minute, 50% of normal dose. The results must be interpreted with caution in patients with malignancy and severe skeletal disease, in whom the nonrenal clearance may vary markedly.

Complexometric determination of clodronate in aqueous solutions and urine.

Three different procedures for the determination of clodronate by means of Th-EDTA-XO or Th-DCTA-XO (XO = xylenol orange) complexes are presented. According to the UV-VIS and 13C NMR measurements, XO is quantitatively replaced by the clodronate anion in the mixed ligand Th-EDTA-XO or Th-DCTA-XO complexes in slightly acidic solutions. This ligand replacement reaction can be applied to the determination of traces of clodronate. Procedures studied involve visual complexometric titration, spectrophotometric titration and conventional spectrophotometric determination. By visual complexometric titration it is possible to determine clodronate directly in human urine with acceptable accuracy and precision in the range 0.5-2.5 mg l-1. By diluting more concentrated urine samples 1:10 with water, samples of up to 80 mg l-1 can be determined with acceptable accuracy and precision. The working range of the method is linear up to 16 mg l-1 in aqueous solutions with the RSD-value varying between 0.7 and 3.8%. Interference caused by the major substances of human urine on the determination were studied.

High-performance liquid chromatographic method for simultaneous determination of clodronate and some clodronate esters.

A quaternary alkylmethylamine-bonded stationary phase has been used for the liquid chromatographic resolution of bisphosphonates. Clodronate and three of its esters were separated by this technique. Nitric acid (30 mM) was used as the mobile phase. The effect of the pH of the mobile phase on the retention, resolution, capacity factor and theoretical plates of the column was examined. Thorium-ethylenediaminetetraacetic acid-xylenol orange mixed ligand complex was used as a postcolumn reagent for bisphosphonates. Bisphosphonates react quantitatively with this complex in slightly acidic solutions, and a change in the absorbance of postcolumn reagent is used as a measure of the bisphosphonate concentration. The relative standard deviation (R.S.D.) values for samples in aqueous solutions were in the range 2.3-15.5% (area) and 1.7-5.9% (height). The detection limits for different compounds, Cmin, varied from 0.3 to 1.4 mg/l (area) and from 0.3 to 0.5 mg/l (height). In urine samples the R.S.D. (%) varied from 3.1 to 18.9 (area) and from 1.1 to 6.3 (height). The linear dynamic range was from the detection limit up to 16 mg/l.

The effect of clodronate (dichloromethylene bisphosphonate) on fluoride kinetics during a 30-day treatment in the rat.

Clodronate (dichloromethylene bisphosphonate) is one of the bisphosphonate drugs preventing the precipitation of calcium phosphates from solution in vitro and inhibiting ectopic calcification and the mineralisation and resorption of bone in vivo. The aim of the experiment was to study the effect of clodronate on fluoride (F) turnover in relation to the concentration of clodronate in blood. The experiment was carried out as a 30-day metabolic study on rats. For all animals the fluoride concentration of drinking water was 5 mg/l. In addition the animals in the experimental group received 10 mg/kg clodronate in one daily subcutaneous injection. The bone and serum mineral concentrations were within the normal range for all animals. The amount of F excreted in urine was also within the same range in the control and test groups in either sex. The amount of clodronate excreted was similar for both sexes. Thus clodronate does not appear to influence fluoride kinetics.

Analysis of (dichloromethylene) bisphosphonate in urine by capillary gas chromatography-mass spectrometry.

An anion exchange extraction method of bisphosphonates from urine is described. More than 90% of the (dichloromethylene) bisphosphonate (Cl2MBP, clodronate) was recovered from urine. The extracted bisphosphonates were trimethylsilylated and analysed with capillary gas chromatography-mass spectrometry (GC/MS). The mass spectrometric techniques used were electron ionization (EI), ammonia chemical ionization (CI), ammonia CI tandem mass spectrometry and methane negative chemical ionization (NCI). The limit of detection of Cl2MBP was 25 pg/injection in the NCI/selective ion recording (SIR)-mode. At 100 ng ml-1 of Cl2MBP the precision of the whole assay method was 17.9% (N = 6). The NCI/SIR technique offers a sensitive and highly selective method for the quantitation of Cl2MBP in urine.

Determination of (dichloromethylene) diphosphonate in physiological fluids by ion-exchange chromatography with phosphorus-selective detection.

An analytical method is presented for the determination of (dichloromethylene) disphosphonate (Cl2MDP) in serum and urine. Cl2MDP is isolated from biological samples by adsorption onto precipitated calcium phosphate. Orthophosphate is separated from Cl2MDP by anion-exchange chromatography using AG 1-X8 resin. Detection is accomplished on-line using a flame photometric detector. Potentially interfering condensed phosphates are removed by acid hydrolysis. Sample handling losses are corrected by monitoring the recovery of a [14C] Cl2MDP spike added to the samples. Determinations of Cl2MDP to concentrations as low as 2 mumol/l are possible. Extension of the method to determine other diphosphonates is discussed.