Determination of amoxycillin in plasma by ion pair column extraction and reversed-phase ion pair high-performance liquid chromatography

Chromatographic analysis of penicillins in pharmaceutical formulations and biological fluids

Natural penicillin (benzylpenicillin) is the oldest antibiotic observed by Alexander Fleming in 1928. To broaden its spectrum of activity, natural penicillin was modified, giving rise to a group of antibiotics under the name 'penicillins'. Although an increasing number of bacteria appear to be resistant to them, penicillins are used to treat a variety of bacterial infections including Gram-positive, Gram-negative aerobic and anaerobic bacteria. Consequently, they are widely used in human and veterinary medicine to prevent and treat diseases. This review covers the analytical methodologies, mainly chromatographic, employed to the penicillins determination in pharmaceutical formulations, biological fluids and in production-scale fermentations reported in the literature. Results of published assays are comparatively presented focusing on sample preparation regarding isolation and purification, chromatographic conditions and method validation. Information on chemical structure, spectrum of activity and action mechanism of common penicillins has also been given.

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.

Application of a semipermeable surface column for the determination of amoxicillin in human blood serum

A high-performance liquid chromatography column-switching system for the automated determination of amoxicillin in human serum was developed as a more efficient alternative for the already existing systems with off-line sample pretreatment. The column-switching system consists of a semipermeable surface (SPS) column and an analytical reversed-phase (RP) C18 column. After centrifuging, pure serum samples were injected into the column-switching system. Clean-up, with regard to removal of proteins, was performed on the SPS column. The fraction containing amoxicillin was concentrated on the analytical RP-C18 column. Finally, chromatography and detection were performed with the RP-C18 column using UV detection at 234 nm. The total analysis time was 15 min. The method has proven to be reliable and to be more time- and resource-efficient compared to previously used methods with off-line sample clean-up. It is now used in bioavailability studies for the development of new amoxicillin formulations.

High-performance liquid chromatographic analysis of amoxicillin in human and chinchilla plasma, middle ear fluid and whole blood

We extended the application of a sensitive high-performance liquid chromatography assay of amoxicillin developed in this laboratory for human plasma and middle ear fluid (MEF) to other sample matrices including chinchilla plasma or MEF and human and chinchilla whole blood with minor modification and validated the limit of quantitation at 0.25 microg/ml with a 50-microl sample size for human and chinchilla plasmas or MEFs. Amoxicillin and cefadroxil, the internal standard, were extracted from 50 microl of the samples with Bond Elut C18 cartridges. The extract was analyzed on a Keystone MOS Hypersil-1 (C8) column with UV detection at 210 nm. The mobile phase was 6% acetonitrile in 5 mM phosphate buffer, pH 6.5 and 5 mM tetrabutylammonium. The within-day coefficients of variation were 2.7-9.9 (n=4) and 1.7-7.2% (n=3) for chinchilla plasma and MEF samples, respectively; 2.8-8.1% (n=3) and 2.9-4.7% (n=3) for human and chinchilla whole blood, respectively. An alternative mobile phase composition for chinchilla plasma and MEF samples reduced the analysis time significantly.

Sensitive assay for measuring amoxicillin in human plasma and middle ear fluid using solid-phase extraction and reversed-phase high-performance liquid chromatography

We developed a sensitive assay to measure amoxicillin in human plasma and middle ear fluid (MEF) using solid-phase extraction and reversed-phase HPLC. Amoxicillin and cefadroxil, the internal standard, were extracted from 50-200 microliters of sample with Bond Elut C18 cartridges. The extract was analyzed on a 15 cm x 2 mm, 5 micron Keystone MOS Hypersil-1 (C8) column with UV detection at 210 nm. The mobile phase was 6% acetonitrile in 5 mM phosphate buffer (pH = 6.5) and 5 mM tetrabutylammonium. The average absolute recovery of amoxicillin and cefadroxil were 91.2 +/- 16.6% and 91.0 +/- 6.8%, respectively. The limit of quantitation was 0.125 microgram/ml with 200 microliters sample size. The linear range was from 0.125 to 35.0 micrograms/ml with correlation coefficients greater than 0.999. These analytic conditions produced a highly sensitive amoxicillin assay in human body fluids without derivatization.

Determination of amoxicillin in human plasma by high-performance liquid chromatography and solid phase extraction

A high-performance liquid chromatographic method using solid phase extraction has been developed for the determination of amoxicillin in human plasma. After concentration of amoxicillin on a C8 cartridge, the cartridge was eluted on-line to a reversed-phase column packed with 5 microns Chromspher C18. The mobile phase was methanol-0.08 M phosphate buffer (pH 7.6) (20:80), which contained 0.01 M tetrabutylammonium dihydrogenphosphate. The column effluent was monitored by UV spectrophotometry at 234 nm. The method has proved to be reliable and is used in bioavailability studies for the development of new amoxicillin formulations.

Use of hydroxypropyl methylcellulose acetate succinate in an enteric polymer matrix to design controlled-release tablets of amoxicillin trihydrate

A controlled-release table of amoxicillin trihydrate was developed by use of a matrix formulation based on the enteric polymer hydroxypropyl methylcellulose acetate succinate (HPMCAS). Sustained drug release was shown by in vitro dissolution testing; the polymer could suppress drug release in the presence of gastric pH but could enhance drug release in the presence of small intestinal pH, compared with compacts of pure drug. Grinding or physical mixing of the drug with the polymer, an alteration in normal compaction pressure, or a substitution of other enteric polymers did not markedly affect drug release from compacts. Physicochemical testing of samples confirmed that the method of mixing did not alter powder morphology. An ethanolic granulation procedure was used in the production of final tablets (21 x 10 mm) containing amoxicillin (750 mg), HPMCAS, anhydrous directly compressible lactose, and lubricants. These large tablets showed a promising sustained-release effect in vitro when a variable-pH-shift dissolution procedure was used. However, single-dose studies with a panel of fasting subjects showed that the tablets had a relative bioavailability of only 64.4%. Other pharmacokinetic parameters confirmed a lack of therapeutic advantage of these tablets over an equivalent dose of conventional capsules.

Simple analysis of amoxycillin in plasma by high performance liquid chromatography with internal standardization and ultraviolet detection

A simple high performance liquid chromatographic method with ultraviolet detection at 229 nm is described for quantitation of amoxycillin in plasma. After deproteination of plasma samples with perchloric acid and adjustment of the pH to 4.9, the supernatant was injected onto a reversed phase C18 column, using acetonitrile:phosphate buffer (0.01 M, pH 7.4) (1:25 v/v) as the mobile phase. Amoxycillin and the internal standard, cefadroxil, were eluted at 23 min and 12 min, respectively, without interference from endogenous substances. Processed samples were stable for at least 24 h at room temperature which permitted automated batch processing overnight. Calibration plots of the amoxycillin to cefadroxil peak-height ratio vs. amoxycillin concentration were linear (P < 0.0001; r > or = 0.995) from 0.25 mg/L to at least 16.0 mg/L. Between-day and within-day imprecision (CV) ranged between 3.7% and 17.7%. Absolute recovery for amoxycillin and cefadroxil exceeded 82%. The application was demonstrated by the analysis of amoxycillin in human plasma after a single oral dose of amoxycillin (250 mg) suspension.

Liquid chromatographic determination of amoxicillin concentrations in bovine plasma by using a tandem solid-phase extraction method

We report a means of determining amoxicillin in bovine plasma by liquid chromatography with UV detection at 235 nm. Purification and concentration of extracts were accomplished by a tandem solid-phase extraction procedure with two reversed-phase columns. Separation of amoxicillin from interferences was improved by the incorporation of a crown ether in the solvent systems used both for the solid-phase extraction and the final high-pressure liquid chromatography. Cefadroxil was added as an internal standard. The average recovery of amoxicillin from plasma (n = 23) was 78.2 +/- 3.0%, and the within-run and between-run coefficients of variation ranged from 1.8 to 7.0%. The detection limit was estimated at 0.1 microgram/ml. This method was used to determine amoxicillin in bovine plasma after intramuscular administration of the drug.

Liquid chromatographic determination of amoxycillin and clavulanic acid in pharmaceutical preparations

A liquid chromatographic method for the simultaneous determination of amoxycillin and potassium clavulanate in tablet and suspension preparations is presented. The method specifies reversed phase column and a buffered mobile phase (CH3OH + KH2PO4-buffer pH 6 + H2O, 15:1:84) isocratically at a rate of 1.0 ml min-1, with detection at 235 nm. The suitability of the chromatographic system developed is tested using replicate injections of the sample and standard preparations. The observed relative standard deviations (RSDs) were within 2%. Recovery experiments conducted utilizing the proposed method gives results of 101.5% +/- 1.72 (n = 6) and 101.22% +/- 1.93 (n = 6) for amoxycillin in tablets and powder for oral administration, respectively. Similarly, recovery experiments for clavulanic acid gave results of 100.33 +/- 1.90 (n = 6) and 99.61 +/- 1.32 (n = 6) in the tablets and suspension powder, respectively. Comparison of the proposed method with the USP method proved it to be satisfactory. The statistical F- and t-tests observed, indicated that there were no significant differences between the two methods regarding precision and accuracy.

Liquid chromatographic determination of amoxicillin and its metabolites in human urine by postcolumn degradation with sodium hypochlorite

A high-performance liquid chromatographic method has been developed for the determination of amoxicillin and its metabolites [(5R,6R)-amoxicilloic acid, the (5S,6R) epimer, and the (2R)-piperazine-2',5'-dione] in human urine. They were separated from the background components of urine on a reversed-phase C18 column using sodium heptylsulphonate as an ion-pairing agent and methanol as an organic mobile phase modifier. The eluent was led to the postcolumn degradation with 1.5 M sodium hydroxide plus 0.02% sodium hypochlorite solution at ambient temperature. The degradation product(s) of each compound was detected at 270 nm. The proposed method permits detection of I, II, III, and IV down to 1 microgram/ml in neat urine samples. At a concentration of 5 micrograms/ml of each compound, within- and between-run precisions (relative standard deviation) were 1.12-5.79 and 0.80-2.70%, respectively. The urinary levels of I and its metabolites were determined by the proposed method after administration of I to humans.