Comparative assay of amoxicillin by high-performance liquid chromatography and microbiological methods for pharmacokinetic studies in calves

A physiological model to evaluate drug kinetics in patients with hemorrhagic shock followed by fluid resuscitation. Application to amoxicillin-clavulanate

PURPOSE

To build a physiologically based pharmacokinetic model describing drug kinetics in interstitial fluid in case of hemorrhagic shock, and to propose a simple method to determine the subset of influential parameters that may be estimated with the data at hand.

METHODS

The model, which accounts for alterations of regional blood flows and body water distribution, was fitted to amoxicillin and clavulanate kinetic data, assessed in 12 trauma patients with hemorrhagic shock by comparison with 12 healthy volunteers. The predictions were the free concentrations of amoxicillin and clavulanate in 14 organs.

RESULTS

In all tissues of trauma patients, the rate of distribution was lower, but the steady-state level was higher than those in healthy participants. Blood volume was reduced by 25% and blood flow in organs other than lung, brain, and heart were reduced by 18%. Compared with healthy subjects, the time that free amoxicillin concentration remained above 8 mg/L in the interstitial fluid of trauma patients was higher in blood and muscles, and lower in the tendon compartment.

CONCLUSIONS

The results and predictions were consistent with the knowledge in this field. The model may be useful to optimize clinical trial designs and drug dosing regimens.

Rapid determination of amoxicillin in premixes by HPLC

A rapid analytical procedure for routine identification and quantification of amoxicillin in premixes by high performance liquid chromatography was developed and tested. The ground premix samples were extracted for 10 min using 100ml extraction mixture water-methanol (800:200, v/v). The extract was analyzed by reversed-phase on Agilent Zorbax SB-C18 column (4.6 mm x 150 mm, i.d., 5 microm particle size) with water-methanol-phosphoric acid-triethylamine (842:150:4:4) containing 10 mM hexane-1-sulfonic acid sodium salt (pH 3.5) as mobile phase. UV detection was carried out at 230 nm. The method was validated for specificity, linearity, solution stability, accuracy, precision, limit of detection, and limit of determination. The detector response for amoxicillin was linear over the selected concentration range from 2.0 to 40.0 mg ml(-1) with a correlation coefficient 0.9999. The mean accuracy was 100.1% with a standard deviation of 0.6%. The limit of detection and the limit of determination are 0.1 and 0.3 mg ml(-1), respectively, which corresponds to 10 and 30 mg kg(-1), respectively, in real premix sample. The sample and standard solutions were stable for 4 h. The method is selective and can be used in routine analysis.

Co-amoxiclav pharmacokinetics during posttraumatic hemorrhagic shock

OBJECTIVE

To determine the effects of severe trauma with hemorrhagic shock on amoxicillin and clavulanate concentrations in plasma and their pharmacokinetics.

DESIGN

A prospective, open, descriptive study.

SETTING

A 12-bed, adult surgical intensive care unit in a university-affiliated hospital in France.

SUBJECTS

Subjects were 12 patients (10 men, 2 women) with severe trauma: median (range) Injury Severity Score, 38 (17-48); Acute Physiology and Chronic Health Evaluation II, 16 (7-38); Simplified Acute Physiology Score II, 41 (23-77). Also enrolled were 12 healthy volunteers who were matched on age (+/-5 yrs), gender, and body-surface area (+/-20 cm2). All the trauma patients suffered hemorrhagic shock defined as the association of at least one episode of systolic blood pressure <90 mm Hg and an intravascular volume expansion >2000 mL between trauma and surgery.

INTERVENTION

Prophylactic perioperative administration of 2 g of amoxicillin and 0.2 g of clavulanate in combination during the first 12 hrs posttrauma in patients, and at the start of the pharmacokinetic study in volunteers.

MEASUREMENTS AND MAIN RESULTS

Serial plasma samples (n = 13) were obtained after the first antibiotic administration to measure antibiotic levels by using high-performance liquid chromatography assays. Compared with volunteers, trauma patients had higher plasma amoxicillin and clavulanate concentrations, attributed to a reduction of the volume of distribution (p =.001 and p =.06, respectively) and, to a lesser extent, of the total body clearance (p =.09 and p =.20, respectively). Consequently, amoxicillin and clavulanate elimination half-lives were similar for the two groups of subjects. The interindividual variabilities for all the amoxicillin pharmacokinetic parameters were higher in patients.

CONCLUSIONS

In trauma patients with hemorrhagic shock requiring surgery, the administration of 2 g of amoxicillin and 0.2 g of clavulanate seems adequate, according to the antibiotic concentrations observed in plasma for both drugs. However, further studies exploring antibiotic concentrations in tissues are warranted.

Determination of amoxicillin in human serum and plasma by high-performance liquid chromatography and on-line postcolumn derivatisation

A high selective, sensitive and fast HPLC method developed for the determination in human serum and plasma. After protein precipitation with perchloric acid, an aliquot of the supernatant was neutralized by mixing it with sodium acetate solution and injected into a C18 HPLC column. Detection was done by a fluorescence detector after on-line postcolumn derivatisation with fluorescamine. The practical limit of quantification was 0.1 microgram/ml using 0.3 ml of plasma. Linearity was given in the tested range of 0.1 to 15 micrograms/ml plasma. Inter-day precision (relative standard deviation) over 7 days for 0.42 micrograms/ml was +/- 7.27%; for 4.54 micrograms/ml, +/- 5.24% and for 13.18 micrograms/ml, +/- 5.25%. Stability over 50 days in serum and plasma occurs at -70 degrees C but not at -20 degrees C (-25 to -35% reduction). This method was used for thousands of human serum and plasma samples.

Automated column liquid chromatographic determination of amoxicillin and cefadroxil in bovine serum and muscle tissue using on-line dialysis for sample preparation

A fully automated method is described for the determination of amoxicillin and cefadroxil in bovine serum and muscle tissue. The method is based on the on-line combination of dialysis and solid-phase extraction for sample preparation, and column liquid chromatography with ultraviolet detection. In order to enhance the UV detectability of the analytes, post-column addition of 0.1 M sodium hydroxide is performed. The method shows good linearity and repeatability for both analytes in serum as well as in muscle tissue; the limits of detection in these samples are 0.05 microgram/ml and 0.2 microgram/g, respectively. The method has a sample throughput of 30 samples per 24 h.