HPLC Method Validation and Pharmacokinetic Study of Alendronate Sodium in Human Urine with Fluorescence Detection

High throughput analysis of alendronate in human samples with derivatization-free hydrophilic-interactive chromatography mass spectrometry

A derivatization-free hydrophilic-interactive chromatography-mass spectrometry (HILIC-MS/MS) method was developed for quantifying low levels of alendronate in human plasma. Alendronate was separated and concentrated using calcium co-precipitation and analyzed by HILIC-MS/MS, requiring only a 300 μL plasma sample for each analysis. The method is simpler, safer, and more environmentally friendly than the conventional LC-MS/MS method that requires solid-phase extraction and derivatization steps during sample pretreatment. The method was validated for selectivity, linearity, precision, accuracy, extraction recovery, matrix effect and limit of quantification. The between-run precisions were no more than 7.1 % with accuracy ranging from - 1.7-6.3 %; extraction recovery was determined to be 85.3 %; while validation results indicated that the method was suitable for accurately quantifying alendronate concentrations in the range from 0.2 to 50 ng/mL. The approach was used successfully for high throughput analysis of alendronate in more than 3700 plasma samples from 120 subjects in a bioequivalence study.

Mechanistic PK-PD model of alendronate treatment of postmenopausal osteoporosis predicts bone site-specific response

Alendronate is the most widely used drug for postmenopausal osteoporosis (PMO). It inhibits bone resorption, affecting osteoclasts. Pharmacokinetics (PK) and pharmacodynamics (PD) of alendronate have been widely studied, but few mathematical models exist to simulate its effect. In this work, we have developed a PK model for alendronate, valid for short- and long-term treatments, and a mechanistic PK-PD model for the treatment of PMO to predict bone density gain (BDG) at the hip and lumbar spine. According to our results, at least three compartments are required in the PK model to predict the effect of alendronate in both the short and long terms. Clinical data of a 2-year treatment of alendronate, reproduced by our PK-PD model, demonstrate that bone response is site specific (hip: 7% BDG, lumbar spine: 4% BDG). We identified that this BDG is mainly due to an increase in tissue mineralization and a decrease in porosity. The difference in BDG between sites is linked to the different loading and dependence of the released alendronate on the bone-specific surface and porosity. Osteoclast population diminishes quickly within the first month of alendronate treatment. Osteoblast population lags behind but also falls due to coupling of resorption and formation. Two dosing regimens were studied (70 mg weekly and 10 mg daily), and both showed very similar BDG evolution, indicating that alendronate accumulates quickly in bone and saturates. The proposed PK-PD model could provide a valuable tool to analyze the effect of alendronate and to design patient-specific treatments, including drug combinations.

Hydroxyapatite surface-functionalized monolithic column for selective in-tube solid phase microextraction of zoleronic acid and risedronic acid

To date, hydroxyapatite (HAP) based monoliths were mainly fabricated by directly doping of HAP, which suffered from less effective coverage of HAP. Herein, a HAP surface-functionalized monolithic column (HAP@PDA@UF) has been prepared by in-situ biomineralization and applied as sorbent for selective in-tube solid phase microextraction of zoleronic acid and risedronic acid. A polydopamine coating was first generated on the surface of the parent urea-formaldehyde resin monolith; and then HAP microcrystals were further grew on the polydopamine coating to achieve this preparation. SEM, EDAX, FTIR, XPS and mercury intrusion method were utilized for the characterization of the HAP@PDA@UF monolith, and provided evidences of this successful preparation. The selective extraction mechanism of the HAP@PDA@UF monolith was investigated by the optimization of methanol percentage in the sampling solution, phosphate concentration in the eluent. Other crucial factors, including sampling and elution flow rate, and collection time span, were also optimized for the desired SPME performance. Under the optimal conditions, the proposed method showed low LODs of 0.1 μg/mL, satisfactory recoveries of 79.6%-92.5% with RSDs less than 2.7%, and good reproducibility with RSD less than 6.9%, which demonstrated the excellent application of the HAP@PDA@UF monolith, and its potential as a promising selective sorbent for bisphosphonates.

Quantitative analysis of bisphosphonates in biological samples

Bisphosphonate drugs pose significant challenges for bioanalysis due to various complicating factors. In 2006, a novel approach, utilizing ‘on-column’ derivatization with diazomethane, was reported that revolutionized the application of liquid-chromatography-tandem mass spectrometry to bisphosphonates bioanalysis. The methodology enables superior biological sample clean-up while transforming bisphosphonates into species amenable to liquid-chromatography-tandem mass spectrometry detection. Since then, the approach has been successfully applied to numerous bisphosphonates. The use of an alternative methylation reagent – trimethylsilyl diazomethane – for on-column derivatization has been reported recently. This review focuses on published methods utilizing on-column derivatization for bioanalysis of major bisphosphonate drugs in biological matrices. Critical points required for successful application of on-column derivatization to the bioanalysis of bisphosphonates will be discussed.

[Influence of mineral water on absorption of oral alendronate in rats]

Alendronate, an oral bisphosphonate (e.g., Fosamax(®)), is effective in the treatment of osteoporosis, and the Fosamax(®) package insert advises that the bioavailability is reduced when taken with mineral water containing high levels of metal cations (Ca(2+), Mg(2+), etc.). However, standards regarding the water used when taking alendronate are unclear. In this study, the influence of mineral water on the absorption of oral alendronate was investigated based on urinary excretion of its unchanged form in rats. Alendronate was diluted in each water sample and administered orally (0.7 mg/kg) to male Wistar rats after 24-hour fast. Urine samples were collected until 24 h after dosing. Urine samples were alkalinized, and alendronate in urine was precipitated as a calcium salt, followed by loading on an anion exchange cartridge. Eluted alendronate was derivatized with 9-fluorenylmethoxycarbonyl (Fmoc) chloride and determined by HPLC with fluorescent detection. Cumulative urinary excretion recoveries of alendronate were calculated from the amounts of urinary excretion. Alendronate was rapidly excreted in the first 6 h, and similar elimination rate constants were seen (from 0.28 to 0.45 h(-1/2)) among the water samples. Cumulative urinary excretion recoveries with tap water, evian(®) and 100% deep ocean water were 0.98±0.17%, 0.80±0.18% and 1.01±0.16% (mean±S.E., n=4). Those with Contrex(®) (0.33±0.07%) were significantly lower when compared with ultrapure water (1.56±0.35%, p<0.01). These findings suggest that the absorption of alendronate decreases based on the calcium concentration of mineral water. In conclusion, mineral water containing high levels of calcium is not recommended when alendronate is taken.

Formulation and in vivo evaluation of sodium alendronate spray-dried microparticles intended for lung delivery

Spray-dried powders for lung delivery of sodium alendronate (SA) were prepared from hydroalcoholic solutions. Formulations display geometric particle size below to 12 μm and spherical shape associated to a hollow structure. The addition of leucine and ammonium bicarbonate leads to porous particles with rough surfaces. The tapped density ranges from 0.016 to 0.062 g/cm(3), decreasing with the increase of the leucine concentration. For all formulations, the calculated aerodynamic diameters are lower than 5 μm. The in vitro aerodynamic evaluation shows that all powders present a high emitted fraction of 100%, a fine particle fraction ranging from 34.4% to 62.0% and an alveolar fraction ranging from to 23.7% to 42.6%. An optimized sample was evaluated regarding sodium alendronate acute pulmonary toxicity and lung bioavailability. The bronchoalveolar lavage study shows that the intratracheal administration of sodium alendronate dry powder and sodium alendronate aqueous solution do not induce significant increases of lung toxicity indicators as compared with the positive control. Moreover, the intratracheal administration of sodium alendronate dry powder results in a 6.23 ± 0.83% bioavailability, a 3.5-fold increase as compared to oral bioavailability. Finally, these results suggest that sodium alendronate pulmonary delivery could be a new and promising administration route.

Application of a semi-automated 96-well format solid-phase extraction, column-switching, fluorescence detection protocol for the determination of alendronate in human urine samples obtained from a bioequivalence study

In the current study, a semi-automated, 96-well format, solid-phase extraction (SPE), analytical column-switching method for alendronate determination in human urine is developed, validated and applied to a bioequivalence study. The current protocol was a substantial improvement of an existing classical method. A robotic liquid handling system was employed to simplify and reduce the time of sample preparation procedure. Automated SPE was carried out using a 96-well cartridge plate and a vacuum control system. Urine samples were determined by applying a column-switching protocol with fluorescence detection. Analysis time, due to the column-switching procedure, was about half of the conventional LC approach (11.5 min instead of 21 min). The method application required the determination of alendronate in urine samples obtained from 96 healthy volunteers as part of a bioequivalence study of two 70 mg alendronate sodium tablets. All major pharmacokinetic parameters of the bioequivalence study were estimated and reported.