High-performance liquid chromatographic determination of amoxicillin in urine using solid-phase, ion-pair extraction and ultraviolet detection

Simultaneous determination of amoxicillin and clavulanic acid in human plasma by isocratic reversed-phase HPLC using UV detection

A simple, rapid and sensitive isocratic reversed phase HPLC method with UV detection using internal standard has been developed and validated for simultaneous determination of amoxicillin and clavulanic acid in human plasma. The assay enables the measurement of amoxicillin and clavulanic acid for therapeutic drug monitoring with a minimum quantification limit of 15 and 30 ng ml(-1), respectively. The method involves simple, one-step extraction procedure and analytical recovery was complete. The separation was carried out in reversed-phase conditions using a Chromolith Performance (RP-18e, 100 mm x 4.6mm) column with an isocratic mobile phase consisting of 0.02 M disodium hydrogen phosphate buffer-methanol (96:4, v/v) adjusted to pH 3.0. The wavelength was set at 228 nm. The coefficients of variation for inter-day and intra-day assay were found to be less than 9.0%.

Simultaneous determination and validation of antimicrobials in plasma and tissue of actinomycetoma by high-performance liquid chromatography with diode array and fluorescence detection

A simple, precise, and reliable chromatographic method was developed for the simultaneous determination in plasma and infected tissue of five antimicrobials proposed for the treatment of actinomycotic mycetoma: amoxicillin, trimethoprim, linezolid, sulfamethoxazole and garenoxacin. Separation of the analytes was achieved on an Atlantis dC18 column (150 mm x 4.6 mm, ID 5 microm) with a mobile phase composed of acetonitrile and trifluoroacetic acid (ATF) 0.1% (v/v) using a gradient program. The detection was carried out using a diode array detector at 254 nm and in a fluorescence detector at wavelengths of excitation and emission of 292 nm and 392 nm for linezolid and sulfamethoxazole, and 292 nm and 408 nm for garenoxacin, respectively. The intraday precision was in the range of 0.7-15% of relative standard deviations (%R.S.D.) for plasma and 1-18% for tissue. Linearity range was from 2.4 to 20 microg/ml for amoxicillin, 0.3 to 20 microg/ml for trimethoprim, sulfamethoxazole and linezolid, and 0.3 to 10 microg/ml for garenoxacin. Acetonitrile was used to precipitate proteins from plasma. Recoveries in plasma ranged from 71% to 118% and in infected tissue from 78% to 122%. Limits of detection (LODs) were 1.2 and 0.5 microg/ml for amoxicillin in plasma and tissue, respectively and 0.15 and 1.2 microg/ml in plasma and tissue, respectively for the other antimicrobials. The method can be applied for individual or simultaneous determination of the antimicrobials in plasma and tissue of mouse infected with actinomycetoma.

Stability evaluation of amoxicillin in a solid premix veterinary formulation by monitoring the degradation products through a new HPLC analytical method

A methodology (by VICH guidelines) for the stability evaluation of amoxicillin in granular premixes is described. This method is based on the monitoring of the degradation products formed during the stability study by a new HPLC-RP method, which has been developed and validated for the simultaneous determination of amoxicillin and its degradation products. The method uses a Nucleosil 120 C18 column and gradient elution. The mobile phase consisted of a mixture of methanol and buffer solution pH 3+/-0.05 at different proportion according to a time-schedule programme, pumped at a flow rate of 1.750 ml min(-1). The DAD detector was set at 230 nm. The validation study was carried out fulfilling the VICH guidelines in order to prove that the new analytical method, meets the reliability characteristics, and these characteristics showed the capacity of analytical method to keep, throughout the time, the fundamental criteria for validation: selectivity, linearity, precision, accuracy, sensitivity (LOD, LOQ) and robustness. The method was applied during the stability study of an amoxicillin premix in order to quantify the drug (amoxicillin) and all its degradation products to evaluate the shelf life of the new veterinary dosage form. The method also proved to be suitable as a rapid and reliable quality control method.

A sensitive assay of amoxicillin in mouse serum and broncho-alveolar lavage fluid by liquid-liquid extraction and reversed-phase HPLC

A sensitive and simple high-performance liquid chromatography (HPLC) method was developed and validated for the analysis of amoxicillin in mouse serum and broncho-alveolar lavage (BAL) fluid. One hundred microlitres of sample were needed for the assay. Sample processing was carried out with liquid-liquid extraction. Cefadroxil was used as an internal standard. The chromatographic separation was achieved on a C18 reversed-phase column with a mobile phase consisting of phosphate buffer, 1-octanesulphonic acid sodium salt and acetonitrile. The detection was conducted at 210 nm. The ranges of the standard curves were 0.2-20 and 0.05-5 microg/ml for serum and BAL samples, respectively. The recoveries of amoxicillin from serum and normal saline were 87 and 88%, respectively. The coefficients of variation were 1.78-6.13% for intra-day and 0.82-6.42% for inter-day analyses. The accuracy was within 100+/-6%. This method was successfully applied to analyze amoxicillin in mouse serum and BAL samples from a pharmacokinetic study.

Development and Validation of a Solid-Phase Extraction-Liquid Chromatographic Method for Determination of Amoxicillin in Plasma

A bioanalytic method for the determination of amoxicillin in plasma by hydrophilic interaction solid-phase extraction and liquid chromatography has been developed and validated. Plasma was precipitated with acetonitrile before samples were loaded onto a zwitterionic hydrophilic interaction liquid chromatography (ZIC-HILIC) solid-phase extraction column. Amoxicillin was analyzed by liquid chromatography on an Aquasil (150 x 4.6 mm) LC column with mobile-phase acetonitrile: phosphate buffer (pH 2.5; 0.1 mol/L) (7:93, v/v) and UV detection at 230 nm. A regression model using 1/concentration weighting was found the most appropriate for quantification. The intraassay precision for plasma was 3.3% at 15.0 microg/mL and 10.9% at 0.200 microg/mL. The interassay precision for plasma was 1.8% at 15.0 microg/mL and 7.5% at 0.200 microg/mL. The total-assay precision for plasma over 4 days using a total of 20 replicates was 13.2%, 5.5%, and 3.8% at 0.200 microg/mL, 3.00 microg/mL, and 15.0 microg/mL, respectively. The lower limit of quantification and the limit of detection were 0.050 microg/mL and 0.025 microg/mL, respectively, for 100 microL plasma. Long-term storage stability studies of amoxicillin in plasma indicate that a temperature of -80 degrees C is necessary to prevent degradation of amoxicillin.

Determination of amoxycillin in human plasma by direct injection and coupled-column high-performance liquid chromatography

This work reports the use of multidimensional HPLC by coupling a restricted access medium (RAM) bovine serum albumin (BSA) octadecyl column (100 x 4.6 mm I.D., 10 microm particle size and 120 A pore size) to an octadecyl Hypersil column (150 x 4.6 mm I.D., 5 microm particle size and 120 A pore size) to the analysis of amoxycillin in human plasma by direct injection. Ion pairing was necessary to extract amoxycillin with good recovery from the plasma proteins. To prepare the spiked samples, aliquots (60 microl) of the appropriated standard solutions were added to each culture tube containing an 180 microl of plasma and a solution of 0.30 mM tetrabuthylammonium phosphate (60 microl). They were vortexed for 15 s and then 290 microl were transferred to autosampler vials. Aliquots (250 microl) of the spiked plasma samples were injected to a column-switching HPLC system. An analysis time of 25 min with no time spent on sample preparation was achieved. The developed method showed good selectivity, sensitivity, accuracy and precision for direct analysis of this polar low wavelength ultraviolet absorption antibiotic using only 180 microl of human plasma. The validated method proved to be reliable and sensitive for the determination of amoxycillin in plasma samples of five healthy volunteers to whom test and reference formulations were administered as an oral dose (500 mg).

Simultaneous determination of amoxicillin and clavulanic acid in human plasma by HPLC with UV detection

A simple and accurate high-performance liquid chromatographic method with ultraviolet detection at 220 nm has been validated for the simultaneous determination of amoxicillin and clavulanic acid in human plasma. Plasma samples were pretreated by direct deproteinization with methanol. A good chromatographic separation between both compounds was achieved using a reversed phase C8 column and a mobile phase, consisting of acetonitrile-phosphate solution-tetramethyl ammonium chloride solution. The calibration curves were linear over the concentration range of 0.625-20 mg l(-1) for amoxicillin and 0.3125-10 mg l(-1) for clavulanic acid with determination coefficients > 0.998. The method is accurate (bias < 7%) and reproducible (intra- and inter-day R.S.D. < 15%), with a quantitation limit of 0.625 and 0.3125 mg l(-1) for amoxicillin and clavulanic acid, respectively. Analytical recoveries from human plasma ranged from 91 to 102% for both components. This fully validated method, which allows the simultaneous measurement of amoxicillin and clavulanic acid in biological samples, is rapid (total run time < 10 min) and requires only a 100 microl sample. This assay is suitable for biomedical applications and was successfully applied to a pilot pharmacokinetics study in healthy volunteers after a single-oral administration of amoxicillin/clavulanic acid combination (500/125 mg).

Simultaneous determination of amoxycillin and clavulanic acid in pharmaceutical dosage forms by LC with amperometric detection

A simple and sensitive liquid chromatographic method with electrochemical (EC) detection is described for the quantitative determination of amoxycillin and clavulanic acid in pharmaceutical dosage forms. Sample components were separated by a reversed phase C18 column, using a mixture of methanol-phosphate buffer (pH 3.2-3.4) (5:95, v/v) as the mobile phase. Detection of antibiotics was performed amperometrically by applying a potential of +1.25 V. High linearity over a concentration range of 15.625-500 ng was demonstrated for amoxycillin (r=0.9999) and clavulanic acid (r=0.9979). Detection limits were 0.8 ng ml(-1) for amoxycillin and 15 ng ml(-1) for clavulanic acid. This method was found to be convenient and reproducible for analysis of these two components in oral suspensions and tablets and might be useful for other pharmaceutical dosage forms.

Ion-pair solid-phase extraction

Solid-phase extraction (SPE) is a technique widely employed by analytical chemists. SPE cartridges are available in a wide variety of formats containing media with diverse chemistries. This paper will review ion-pair SPE, one of the less frequently applied, and presumably less well-known techniques. Advantages of this technique over more conventional reversed-phase or ion-exchange SPE include selectivity, compatibility with rapid evaporative concentration, and potential application to multiclass multiresidue analysis.

Determination of amoxicillin in plasma samples by capillary electrophoresis

We have developed a capillary zone electrophoresis (CZE) method for determining amoxicillin in animal plasma samples. Sample clean-up involved solid-phase extraction onto Sep-Pak C18 cartridges followed by elution with water-methanol (85:15). This paper describes two different techniques to increase the sensitivity of the CZE method: field-amplified sample injection (FASI) and electrokinetic injection. We have enhanced the detection limit to 280 micrograms l-1 by the FASI technique.

Improved high-performance liquid chromatographic determination of amoxicillin in human plasma by means of column switching

A highly sensitive and selective HPLC method was developed for the determination of amoxicillin in human plasma. After addition of buffer and internal standard, the sample was ultrafiltered and injected on to a precolumn to remove polar plasma interferences. Detection was effected with a UV detector set at 230 nm. The limit of quantification for amoxicillin was 50.1 ng/ml with an imprecision of 4.2% using 0.25 ml of plasma. Linearity was confirmed over the whole calibration range (25.4-0.0501 micrograms/ml) and the inter-day variation ranged from 2.0 to 4.5%. The method was validated according to GLP guidelines and its suitability was demonstrated by the analysis of several hundred samples in a bioequivalence study. The method can be used to determine pharmacokinetic parameters of amoxicillin in humans after a single oral dose of 500 mg.

Determination of the angiotensin-converting enzyme inhibitor lisinopril in urine using solid-phase extraction and reversed-phase high-performance liquid chromatography

A simple, accurate and precise high-performance liquid chromatographic method is described for assaying lisinopril in human urine. Urine (1 ml) containing lisinopril and enalaprilat (internal standard) was acidified with 10 microliters of 6 M nitric acid, passed through a Sep-Pak C18 cartridge and eluted with 3 ml of 10% acetonitrile, followed by 6 ml of distilled water. the separations were carried out using a mu Bondapak c18 column with a mobile phase comprising acetonitrile (60 ml), methanol (10 ml) and tetrahydrofuran (10 ml) in 15 mM phosphate buffer (920 ml) at pH 2.90. Separations were performed at 40 degrees C and detection was at 206 nm. Standard calibration plots of lisinopril in urine were linear (r > 0.998) and recovery was greater than 64%. The lowest quantifiable concentration was 0.5 micrograms/ml. Within-day and between-day imprecision (coefficient of variation) ranged from 2.51% to 9.26%, and inaccuracy was less than 8.3%.

Analytical strategies for the screening of veterinary drugs and their residues in edible products

The development of analytical strategies for the regulatory control of drug residues in food-producing animals is discussed. Analytical methods for the determination of veterinary drugs in edible products are based on microbiological, immunochemical and physicochemical principles. Because of complexity of biological matrices such as egg, milk and meat, well designed, and often sophisticated, off-line or on-line sample treatment procedures are essential, especially when utilising physicochemical multi-residue screening procedures. Since large series of samples have often to be analysed, automation is increasingly becoming important. Confirmation of the identity of drug residues and validation of the analytical results implies the use of adequate analytical methods. In its turn, this requires well established criteria for those methods and/or equivalent reference methods.

Determination of dose-dependent absorption of amoxycillin from urinary excretion data in healthy subjects

Measurement of unchanged drug in urine was used to study the rate and extent of amoxycillin absorption after administration of amoxycillin sodium solution to six healthy subjects in a Latin-Square crossover design. The mean (95% CI) fraction of the dose excreted as unchanged amoxycillin decreased (P < 0.05) from 0.50 (0.44-0.56) after 97 mg amoxycillin sodium (= 0.25 mmol amoxycillin) to 0.23 (0.19-0.27) after 3103 mg (8 mmol), while the mean residence time determined from urinary excretion rate data increased (P < 0.05) from 1.54 (1.32-1.76) h to 2.16 (2.01-2.41) h. Plots of total urinary excretion and initial (0-30 min) excretion of unchanged drug vs dose indicated significant non-linearity above 776 mg doses. Michaelis-Menten parameters describing this relationship with respect to amount absorbed were 3.02 mmol for maximum amount absorbed and 1.93 mmol for amount absorbed at half maximum for 0-30 min. These results support a saturable absorption mechanism for amoxycillin which had clinical implications for high oral amoxycillin doses, and for competition with other drugs having capacity-limited absorption.