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

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.

Simultaneous determination of amoxicillin and ranitidine in rat plasma by high-performance liquid chromatography

A high-performance liquid chromatography method using ultraviolet detection at 230 nm for the simultaneous determination of amoxicillin and ranitidine in rat plasma has been validated. Plasma samples after pretreatment with acetonitrile to effect deproteinization were dried under N2 and reconstituted with water. The standard calibration curves for amoxicillin and ranitidine were linear (r2=0.9999) over the concentration range of 0.2-20 microg ml-1 and 0.03-6 microg ml-1 in rat plasma, respectively. The intra- and inter-day assay variability range for amoxicillin was 2.4-8.5% and 3.2-11.7%, and for ranitidine was 1.7-9.0% and 4.5-10.1%, respectively. This method has been successfully applied to a pharmacokinetic study after oral coadministration of amoxicillin and ranitidine to rats.

A liquid chromatographic method for simultaneous determination of amoxicillin sodium and sulbactam sodium in a combination formulation

An isocratic liquid chromatographic method with UV detection at 210nm is described for simultaneous determination of amoxicillin sodium and sulbactam sodium in a new combination formulation. Chromatographic separation of the two drugs was achieved on a Hypersil C(18) column using a mobile phase consisting of a binary mixture of methanol and 0.01mol/l sodium acetate (5:95, v/v). The commonly used paired-ion aqueous mobile phase for the determination of penicillins was avoided in this study. The developed LC method offers symmetric peak shape, good resolution and reasonable retention time for both drugs. Linearity, accuracy and precision were found to be acceptable over the concentration ranges of 155.3-1553.0microg/ml for amoxicillin sodium and 45.0-450.0microg/ml for sulbactam sodium. The proposed LC method can be used for the quality control of formulated products containing these two drugs.

Comparative study of the micellar enhanced spectrophotometric determination of beta-lactamic antibiotics by batch and flow injection analysis using a multisimplex design

A study has been made on the spectrophotometric determination of the beta-lactamic antibiotics, amoxicillin and ampicillin, in micellar media using Cu ions as catalyst. Batch and flow injection approaches were compared. Multisimplex design was used to determine the optimal values of the flow injection analysis (FIA) system. Chemical (buffer, pH and Cu(II) concentrations) and physical (flow rate, temperature and reaction coil length) variables were considered. The analytical performance characteristics were as follows: the detection limits for batch and flow-through systems were 2.5 x 10(-7) and 2 x 10(-6) M, respectively, and a relative standard deviation less than 1% was found for both methods. The proposed FIA methodology was satisfactorily applied to the determination of the antibiotics in pharmaceutical formulations.

Measurement of amoxicillin in plasma and gastric samples using high-performance liquid chromatography with fluorimetric detection

A rapid, selective and sensitive HPLC assay has been developed for the routine analysis of amoxicillin in rat plasma, gastric juice aspirate and gastric tissue which is applicable to low concentrations of amoxicillin (<1 microg mL(-1)) or small sample volumes. Amoxicillin was converted, via an internal rearrangement, to form a fluorescent product which was subsequently recovered using liquid-liquid extraction. A Kromasil ODS 3 microm (150 x 3.2 mm I.D.) column was maintained at 40 degrees C and used with a mobile phase consisting of methanol-water (55:45, v/v). Fluorimetric detection was at an lambda(ex) of 365 nm and an lambda(em) of 445 nm. The limits of quantitation for amoxicillin were 0.1 microg mL(-1) for gastric juice aspirate (500 microL), 0.5 microg mL(-1) for plasma (50 microL) and 0.075 microg g(-1) for gastric tissue (250 mg). The method was linear up to at least 15 microg mL(-1) in gastric juice aspirate, up to 200 microg mL(-1) in plasma and up to 100 microg g(-1) in gastric tissue, with inter- and intra-day RSDs being less than 19%. The assay has been applied to the measurement of amoxicillin in rat plasma, gastric juice aspirate and gastric tissue for pharmacokinetic studies in individual rats.

Microdialysis studies of the middle ear distribution kinetics of amoxicillin in the awake chinchilla

This work was performed to develop an experimental animal model for the study of antibiotic drug distribution into middle ear fluid (MEF) and to evaluate its relevance and significance to the clinical treatment of otitis media (OM). Chinchillas were assigned to normal or infected ear groups after Eustachian tube obstruction (ETO) or direct trans-bullar inoculation with type 3 Streptococcus pneumoniae. Following survival surgery to implant microdialysis (MD) probes in the jugular vein and middle ear (ME), amoxicillin was given intravenously (iv) as a bolus or infusion. Drug concentrations in blood and MEF were continuously monitored by microdialysis. The measured concentrations were corrected for probe recovery by simultaneous retrodialysis. Multiple MEF and blood sampling was also performed to validate the animal model and MD sampling technique. Bacterial infection was successfully induced 3-7 days after the inoculation, whereas the control group gave negative bacterial culture results. The beta-lactam antibiotic, amoxicillin, exhibited an elimination half-life of 0.33+/-0.23 h (n = 9) in chinchilla blood, 1.46+/-0.50 h (n = 5) and 1.75+/-0.84 h (n = 4) in MEF of normal and infected ears (p = 0.6), respectively. MEF-to-blood amoxicillin concentration ratios at steady state following iv infusion were 0.26+/-0.06 (n = 5) and 0.28+/-0.11 (n = 4) for normal and infected ears (p = 0.7), respectively. MD allows continuous monitoring of drug concentration-time profiles in blood and MEF in an awake chinchilla model. The concentrations measured by MD were validated by direct sampling. The ratio of the area under the curve (AUC) of drug concentration in MEF versus time to that in blood after iv bolus doses was less than unity, as was the steady-state concentration ratio following constant-rate iv infusion, suggesting an active transport mechanism was involved in the efflux of amoxicillin from the ME of chinchilla. The results of studies involving infected ears were not significantly different from those in normal ears in terms of amoxicillin distribution across the ME mucosal membrane after systemic administration.

Amoxicillin middle ear fluid penetration and pharmacokinetics in children with acute otitis media

BACKGROUND

Acute otitis media (AOM) is a common childhood infectious disease. The efficacy of antibiotic dosing regimens is usually assessed by antibiotic plasma pharmacokinetics or middle ear fluid (MEF) concentration at one or two time points. Viral coinfection in AOM reduced antibacterial efficacy of antibiotics.

OBJECTIVE

To determine amoxicillin MEF penetration and pharmacokinetics in bacterial and combined bacterial and viral AOM.

METHODS

Thirty-four children with AOM were enrolled, and MEF was collected by tympanocentesis for bacterial culture and viral studies. Nasal wash and venous blood were also obtained for viral culture and serologic studies, respectively. Subjects were treated with amoxicillin 40 mg/kg/day orally, divided in equal doses every 8 h. During the second visit (48 to 72 h later) the subjects, with the regular morning amoxicillin dose withheld, were given an oral amoxicillin dose of 25 mg/kg. Thereafter two blood samples and one MEF sample by tympanocentesis were collected from each child at selected times between 0.5 and 4.0 h after dosing for bacterial and viral studies and amoxicillin concentration determination by high performance liquid chromatography.

RESULTS

Eleven (37%) children had only bacterial infection, 6 (20%) had viral infection only, 6 (20%) had both bacterial and viral infections and in 7 (23%) neither bacterial nor viral pathogens were recovered. MEF bacterial culture was positive in 23 of 40 ears (57.5%) before treatment with amoxicillin (40 mg/kg/day) and was still positive in 4 of 38 ears (10.5%) after 2 to 3 days of treatment. Amoxicillin plasma concentration reached its peak at 1.0 to 1.5 h after a 25-mg/kg oral dose. The estimated MEF concentration peak occurred 3.0 h after the dose with MEF concentrations ranging from undetectable to 20.6 microg/ml and a mean of approximately 9.5 microg/ml. Geometric mean amoxicillin concentrations were lowest in virus-infected children (2.7 microg/ml), nearly the same in culture-negative samples from children without viral infection (2.9 microg/ml), higher in children with combined bacterial and viral infection (4.1 microg/ml) and highest in children with bacterial-only infection (5.7 microg/ml).

CONCLUSIONS

MEF amoxicillin penetration tended to be lower in children with viral infection. The current amoxicillin dosing recommendation of 40 mg/kg/day in three divided dose is inadequate to effectively eradicate resistant Streptococcus pneumoniae, particularly during viral coinfection. A dosing regimen of 75 to 90 mg/kg/day is recommended for AOM.