Paired ion reversed-phase HPLC assay for the determination of iothalamic acid and para aminohippuric acid in urine

HPLC-UV Method Validation for Amobarbital and Pharmaceutical Stability Evaluation When Dispersed in a Hyaluronic Acid Hydrogel: A New Concept for Post-Traumatic Osteoarthritis Prevention

A mitochondrial electron transport chain member complex I inhibitor, amobarbital, can reduce oxidative damage and chondrocyte death, eventually preventing post-traumatic osteoarthritis (PTOA). Viscosupplementation using a crosslinked hyaluronic acid (HA) hydrogel is currently applied clinically for knee OA pain relief. In this work, we utilized the HA hydrogel as a drug delivery vehicle to improve the long-term efficacy of amobarbital. Here we evaluated the pharmaceutic stability of amobarbital when dispersed in a crosslinked HA hydrogel formulated in proportions intended for clinical use. We validated a high-performance liquid chromatography with an ultraviolet detector (HPLC-UV) method following International Conference for Harmonization Q2(R1) guidelines to ensure its suitability for amobarbital detection. The feasibility of this formulation's drug delivery capability was proven by measuring the release, solubility, and drug uniformity. The amobarbital/HA hydrogel showed comparable amobarbital stability in different biological fluids compared to amobarbital solution. In addition, the amobarbital/HA hydrogel imparted significantly greater drug stability when stored at 70°C for 24 hours. In conclusion, we confirmed the pharmaceutical stability of the amobarbital/HA hydrogel in various conditions and biological fluids using a validated HPLC-UV method. This data provides essential evidence in support of the use of this amobarbital/HA formulation in future clinical trials for PTOA treatment.

HPLC estimation of iothalamate to measure glomerular filtration rate in humans

Glomerular filtration rate (GFR) is usually determined by estimation of iothalamate (IOT) clearance. We have developed and validated an accurate and robust method for the analysis of IOT in human plasma and urine. The mobile phase consisted of methanol and 50 mM sodium phosphate (10:90; v/v). Flow rate was 1.2 mL/min on a C18 reverse phase column, Synergi-hydro (250 × 4.6 mm) 4 µm 80 Å, with an ultraviolet detector set to 254 nm. Acetonitrile was used for the deproteination and extraction of IOT from human plasma and urine. Precision and accuracy were within 15% for IOT in both plasma and urine. The recoveries of IOT in urine and plasma ranged between 93.14% and 114.74 and 96.04-118.38%, respectively. The linear range for urine and plasma assays were 25-1500 and 1-150 µg/mL respectively. The lower limits of detection were 0.5 µg/mL for both urine and plasma, with no interference from plasma and urine matices. This method has been fully validated according to FDA guidelines and the new HPLC assay has been applied to a new formulation of IOT (Conray™ 43), to calculate GFR in healthy volunteers. The new method is simple, less expensive and it would be instrumental in future clinical and pharmacokinetic studies of iothalamate in kidney patients.

A novel, simple and inexpensive procedure for the simultaneous determination of iopamidol and p-aminohippuric acid for renal function assessment from plasma samples in awake rats

The purpose of the current study was to design, validate and implement a novel analytical method for the simultaneous plasma measurement of iopamidol and p-aminohippuric acid (PAH) to estimate renal function in awake rats. A reverse-phase high performance liquid chromatographic (RP-HPLC) method for the simultaneous measurement of iopamidol (for glomerular filtration rate estimation, GFR) and PAH (for tubular secretion determination, TS) was designed and validated using a C-18 column, 0.1M acetic acid-10% acetonitrile (90:10, v/v) as mobile phase, at a flow rate of 0.3 ml/min, and UV detection at 270 nm. Iopamidol (244.8 mg/kg) was administered intravenously followed immediately by sodium PAH (100 mg/kg) to healthy female Sprague-Dawley rats. Plasma samples obtained at 2.5, 5, 10, 15, 20, 30, 45, 60, 90, and 120 min after drug administration were deproteinized with 2.5% trichloroacetic acid containing p-aminobenzoic acid as internal standard, and separated by the validated RP-HPLC method described above. The iopamidol and PAH chromatographic data were analyzed using a non-compartmental model. The results demonstrated that the RP-HPLC method was linear in ranges between 15-120 μg/ml and 2.5-120 μg/ml for iopamidol and PAH, respectively. Precision and accuracy were within 15% for both drugs. Recovery of iopamidol and PAH was 92% and 100%, respectively. Plasma iopamidol and PAH clearances in awake rats, estimates for GFR and TS, respectively, were 1.49±0.20 ml/min and 3.73±0.38 ml/min. In conclusion, the method here described is a simple and reliable procedure, for the simultaneous and time-saving determination of GFR and TS from plasma samples in the conscious rat.

Development of a liquid chromatography tandem mass spectrometry method for iothalamate measurement to assess renal function for potential kidney donation

BACKGROUND

Chronic kidney disease often goes undetected due to the insensitivity of current methods to accurately assess glomerular filtration rate (GFR) in early stages of renal dysfunction. The clearance of exogenously introduced iothalamate, a commonly used radiopaque agent, is an alternative to inulin clearance for the assessment of renal function and its use in calculating GFR can serve as a screening tool for kidney transplant donors.

METHODS

A method was developed to measure iothalamate in plasma and urine samples by HPLC combined with electrospray positive ionization tandem mass spectrometry (MS/MS). Iothalamate is isolated from plasma by methanol extraction and urine using a quick-spin filtration approach, then monitored by multiple reaction monitoring using the hydrogen adduct mass transitions. Iohexol was used as an internal standard.

RESULTS

Iothalamate was measured within an analytical run time of 5 min, with a lower limit of quantification of 18.75 ng/ml. The intraassay and interassay variations of the plasma and urine iothalamate assays were both <9%. Recovery from plasma and urine samples ranged from 93.6% to 104.1%. GFR was calculated using the patient's urine flow rate and plasma and urine iothalamate values. Linear correlations tested by LC-MS/MS and an accepted capillary electrophoresis (CE) assay showed similar results (GFR, r=0.92, Sy/x=10.3).

CONCLUSIONS

We developed and validated an LC-MS/MS method for quantitating iothalamate in plasma and urine to calculate GFR used for screening potential kidney donors in our hospital system. A less sensitive mass spectrometry system does not sacrifice analytical or clinical sensitivity for measuring GFR.

High performance liquid chromatographic measurement of iothalamate in human serum and urine for evaluation of glomerular filtration rate

A simple and sensitive HPLC-UV assay was developed for the measurement of iothalamate (IOT) in human serum and urine. Chromatographic separation was achieved using an embedded-carbamate-group bonded RP18 column and mobile phase consisting of 50 mM monobasic sodium phosphate and methanol (90:10, v/v) without the addition of ion-pair reagents. The assay demonstrated a high analytical reliability within the IOT concentration range of 1-150 microg/ml in serum and 25-1500 microg/ml in urine. The relative standard deviations (RSDs) for intra- and inter-day analysis were less than 5.1% in all cases. This method has been used for the evaluation of glomerular filtration rate (GFR) in subjects participating in a phase I clinical trial of a novel antimalarial medicine. The average baseline GFR was 100.41+/-19.99 ml/min/1.73 m(2) in 119 healthy volunteers. The assay may also allow the simultaneous measurements of p-aminohippuric acid (PAH), N-acetyl PAH (aPAH), and IOT with some modification. PAH, IOT, aPAH, and beta-hydroxyethyl-theophylline internal standard peaks appeared approximately at 2.5, 3.7, 5.9, and 11.8 min, respectively, in an isocratic run.

Determination of fosfomycin in pus by capillary zone electrophoresis

A method is described for the determination of fosfomycin in pus by capillary zone electrophoresis with reversed electroosmotic flow, and indirect UV absorbance detection. Sample pre-treatment is limited to removal of proteins and cell debris by adding the double volume of methanol, followed by vortexing for few seconds, and centrifugation at 15,000 x g for 2 min. The supernatant is directly injected into the instrument. Fosfomycin is separated from sample constituents with a background electrolyte at pH 7.25 (25 mM benzoate buffer with 0.5 mM hexadecyltrimethylammonium bromide added, adjusted to pH with tris(hydroxymethyl)-aminomethane (TRIS)). Separation is carried out in a capillary with 50 microm I.D., 64.5 cm total length, 56.0 cm to the detector, at 25 degrees C with -25 kV voltage applied. Due to the low absorbance of the analyte, indirect UV detection was performed at 254 nm using a bubble cell capillary. Sample was injected by pressure (450 mbar s). Repeatability for fosfomycin in spiked pus (from 8 or 10 consecutive injections of three different series at concentrations of 100 microg/mL of the antibiotic) was between 2.4 and 8.2% relative standard deviation (RSD). Accuracy (expressed as recovery of fosfomycin determined by three independent analysis at 10, 100 and 300 microg/mL fosfomycin added to plain pus) was between 75 and 102%. Intermediate reproducibility (n = 9 at three different days) was between 2 and 12% RSD. Limit of detection and limit of quantitation were 4.5 and 15 microg/mL, respectively. The concentration of fosfomycin in pus of patients treated with the antibiotic ranged up to 240 microg/mL. The concentration of other anionic pus constituents identified beside chloride (acetate, succinate, lactate, phosphate) ranged between 20 and 7800 microg/mL.

Alternative high-performance liquid chromatographic assay for p-aminohippuric acid (PAH): effect of aging on PAH excretion in the isolated perfused rat kidney

Para-aminohippuric acid (PAH), an indicator of renal plasma flow, is a commonly used marker of organic anion transport by the kidney. An analytical method for PAH using HPLC was developed. The method is simple, fast and requires a minimum amount of organic solvent. Sample preparation involved protein precipitation with zinc sulfate. Para-amino benzoic acid was utilized as an internal standard (IS). Chromatography was performed using a reversed-phase phenyl column with UV detection at a wavelength of 254 nm. Mobile phase consisted of 0.1 M acetic acid and acetonitrile (99:1) at a flow rate of 1 ml/min. The assay was validated over a standard concentration range from 1 to 25 microg/ml. Accuracy, precision, reproducibility and specificity of the method was established with coefficients of variation <10%. The method was sensitive and showed linear response in peak height ratio (analyte:IS) over the concentration range studied (r(2)>0.99). The assay was used to study the effect of aging on PAH excretion in the isolated perfused rat kidney model. Experiments were conducted in kidneys from young (2-3 months, n=6), adult (6-9 months, n=5) and aged (12-16 months, n=3) male Sprague-Dawley rats at an initial drug concentration of 20 microg/ml. Significant differences in kidney function (e.g. glomerular filtration rate and glucose reabsorption) were observed in aged kidneys. Despite a 5-fold reduction in glomerular filtration rate, PAH renal clearance (kidney weight-corrected) decreased by only 2-fold in aged (2.2+/-0.42 ml/min per gram) compared to young (4.6+/-0.70 ml/min per gram, P<0.05) rats. Furthermore, renal excretion ratio was significantly higher in aged rats (27+/-8.0 vs. 15+/-5.0, P<0.05). These preliminary findings challenge the 'Whole Nephron Hypothesis' that assumes parallel reductions in renal filtration and secretory capacity secondary to disease or aging.