Determination of Penicillinase-Resistant Penicillins In Serum Using High-Pressure Liquid Chromatography

Daily serum piperacillin monitoring is advisable in critically ill patients

The aim of the present study was to evaluate the benefit of monitoring serum piperacillin concentrations in critically ill patients. This was an 11-month, prospective, observational study in a 30-bed Intensive Care Unit in a teaching hospital, involving 24 critically ill patients with evidence of bacterial sepsis. All patients received a 66 mg/kg intravenous bolus of piperacillin in combination with tazobactam (ratio 1:0.125) followed by continuous infusion of 200mg/kg/24h. The dosage was adjusted when the serum piperacillin concentration either fell below 4x the drug's minimum inhibitory concentration (MIC) for the causative agent or exceeded the toxic threshold of 150 mg/L. With the initial regimen, serum piperacillin concentrations were within the therapeutic target range in only 50.0% of patients (n=12). This proportion increased to 75.0% (18 patients) (P=0.006) following dosage adjustment. For patients with low initial serum piperacillin concentrations (n=8), the percentage of time during which the concentration remained above 4x MIC (%T>4x MIC) was 7.1+/-5.9% before dosage adjustment and 27.3+/-8.6% afterwards. In conclusion, in critically ill patients, monitoring and adjustment of serum piperacillin levels is required to prevent overdosing and might also help to correct underdosing, an important cause of antibiotic therapy failure.

Pharmacokinetics of an ampicillin–sulbactam combination after intravenous and intramuscular administration to neonatal calves

The pharmacokinetics of a 2:1 ampicillin-sulbactam combination after intravenous (i.v.) and intramuscular (i.m.) injection at a single dose rate of 20 mg/kg bodyweight (13.33 mg/kg of sodium ampicillin and 6.67 mg/kg of sodium sulbactam) were studied in 10-day-old neonatal calves (n = 10). The plasma concentration-time data of both antibiotics were best fitted to an open two-compartment model after i.v. administration. After i.m. administration, an open two-compartment model demonstrated first order absorption. The apparent volumes of distribution of ampicillin and sulbactam, calculated by the area method, were 0.20+/-0.01 and 0.18+/-0.01 L/kg, respectively, and the total body clearances were 0.51+/-0.03 and 0.21+/-0.01 L/kg h. The elimination half-lives of ampicillin after i.v. and i.m. administration were 0.99+/-0.03 and 1.01+/-0.02 h, respectively, whereas for sulbactam the half-lives were 2.24+/-0.02 and 3.44+/-0.94 h. The bioavailability after i.m. injection was high and similar for both drugs (70.31+/-0.2% for ampicillin and 68.62+/-4.44% for sulbactam). The mean peak plasma concentrations of ampicillin and sulbactam were reached at similar times (0.47+/-0.02 and 0.72+/-0.01 h, respectively) and peak concentrations were also similar but not proportional to the dose administered (17.88+/-0.91 mg/L of ampicillin and 12.92+/-0.79 mg/L of sulbactam). Both drugs had similar pharmacokinetic behaviour after i.m. administration. Since the plasma concentrations of sulbactam were consistently higher during the elimination phase of their disposition, consideration could be given to formulating the ampicillin-sulbactam combination in a ratio higher than 2:1.

Pharmacokinetics of a combination preparation of ampicillin and sulbactam in turkeys

OBJECTIVE

To investigate the disposition kinetics of ampicillin and sulbactam after IV and IM administration of an ampicillin-sulbactam (2:1) preparation and determine the bioavailability of the combined preparation after IM administration in turkeys.

ANIMALS

10 healthy large white turkeys.

PROCEDURE

In a crossover study, turkeys were administered the combined preparation IV (20 mg/kg) and IM (30 mg/kg). Blood samples were collected before and at intervals after drug administrations. Plasma ampicillin and sulbactam concentrations were measured by use of high-performance liquid chromatography; plasma concentration-time curves were analyzed via compartmental pharmacokinetics and noncompartmental methods.

RESULTS

The drugs were distributed according to an open 2-compartment model after IV administration and a 1-compartment model (first-order absorption) after IM administration. For ampicillin and sulbactam, the apparent volumes of distribution were 0.75+/-0.11 L/kg and 0.74+/-0.10 L/kg, respectively, and the total body clearances were 0.67+/-0.07 L x kg(-1) x h(-1) and 0.56+/-0.06 L x kg(-1) x h(-), respectively. The elimination half-lives of ampicillin after IV and IM administration were 0.78+/-0.12 hours and 0.89+/-0.17 hours, respectively, whereas the corresponding half-lives of sulbactam were 0.91+/-0.12 hours and 0.99+/-0.16 hours, respectively. Bioavailability after IM injection was 58.87+/-765% for ampicillin and 53.75+/-5.35% for sulbactam.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that a regimen of loading and maintenance doses of 300 mg of the ampicillin-sulbactam (2:1) combination/kg every 8 hours could be clinically useful in turkeys. This dosage regimen maintained plasma concentrations of ampicillin > 0.45 microg/mL in turkeys.

Simultaneous determination of ticarcillin and clavulanate in rabbit serum and tissue cage fluid by liquid chromatography

A gradient elution HPLC method with a wavelength switch technique was developed to simultaneously analyze the beta-lactam ticarcillin and the beta-lactamase inhibitor clavulanate in rabbit serum and tissue cage fluid (TCF). A C18 reversed-phase column with a programmable UV detector changing the wavelength from 218 to 254 nm at 9 min was used for chromatographic separation. The mobile phase consisted of acetonitrile, phosphate buffer and tetrabutylammonium hydrogen sulfate by following a gradient elution program at a flow-rate of 1 ml/min. Sample processing was carried out with liquid-liquid extraction. Good linearity, recoveries, precision and accuracy were obtained. The ranges of the standard curves were 1-100 microg/ml for ticarcillin, and 0.2-20 microg/ml for clavulanate. This assay has been successfully applied to analyze ticarcillin and clavulanate in rabbit serum and tissue cage fluid samples from a pharmacokinetic study.

Pharmacokinetics of an ampicillin/sulbactam (2:1) combination in rabbits

The pharmacokinetics of a 2:1 ampicillin-sulbactam combination in six rabbits, after intravenous and intramuscular injection at a single dosage of 20 mg/kg bodyweight (13.33 mg/kg of sodium ampicillin and 6.67 mg/kg of sodium sulbactam) were investigated by using a high performance liquid chromatographic method for determining plasma concentrations. The plasma concentration-time curves were analysed by compartmental pharmacokinetic and noncompartmental methods. The disposition curves for both drugs were best described by an open two-compartment model after intravenous administration and a one-compartment model with first order absorption after intramuscular administration. The apparent volumes of distribution calculated by the area method for ampicillin and sulbactam were 0.62 +/- 0.09 and 0.45 +/- 0.05 L/kg, respectively, and the total body clearances were 0.65 +/- 0.04 and 0.42 +/- 0.05 L/kg h, respectively. The elimination half-lives of ampicillin after intravenous and intramuscular administration were 0.64 +/- 0.11 and 0.63 +/- 0.16 h, respectively, whereas for sulbactam the half-lives were 0.74 +/- 0.12 and 0.77 +/- 0.17 h, respectively. The bioavailability after intramuscular injection was high and similar in both drugs (73.34 +/- 10.08% for ampicillin and 83.20 +/- 7.41% for sulbactam). The mean peak plasma concentrations of ampicillin and sulbactam were reached at similar times (0.20 +/- 0.09 and 0.34 +/- 0.15 h, respectively) and peak concentrations were also similar but nonproportional to the dose of both products administered (13.07 +/- 3.64 mg/L of ampicillin and 8.42 +/- 1.74 mg/L of sulbactam). Both drugs had similar pharmacokinetic behaviour after intramuscular administration in rabbits.

Some pharmacokinetic parameters of ampicillin/sulbactam combination after intravenous and intramuscular administration to goats

Some pharmacokinetic parameters of an ampicillin/sulbactam (2:1) combination were studied in six goats, after intravenous and intramuscular injection at a single dosage of 20 mg/kg bodyweight (13.33 mg/kg of sodium ampicillin and 6.67 mg/kg of sodium sulbactam). The drugs were distributed according to an open two-compartment model. The apparent volumes of distribution calculated by the area method of ampicillin and sulbactam were 0.34 +/- 0.04 l/kg and 0.45 +/- 0.15 l/kg, respectively, and the total body clearances were 0.72 +/- 0.11 and 0.38 +/- 0.07 l/kg.h. The half-lives of ampicillin after intravenous and intramuscular administration were 0.32 +/- 0.04 h and 0.71 +/- 0.14 h, respectively. For sulbactam the half-lives were 0.79 +/- 0.18 h and 1.13 +/- 0.21 h after administration by the same routes. The bioavailability after intramuscular injection was high and similar for both drugs (98.29% for ampicillin and 101.84% for sulbactam). The mean peak plasma levels of ampicillin (0.43 +/- 0.27 h) and sulbactam (0.34 +/- 0.14 h) were reached at a similar time, and peak concentrations were also similar and non-proportional to the dose of the products administered (11.02 +/- 3.11 mg/l of ampicillin and 9.5 +/- 0.98 mg/l of sulbactam).

High-performance liquid chromatographic assay for meropenem in serum

High-performance liquid chromatographic procedures have been developed for the measurement of meropenem in serum. The separation was performed on an Ultrasphere XL-ODS analytical column (75 x 4.6 min I.D.). The mobile phase consisted of 10.53 mmol/l ammonium acetate-acetonitrile (95:5, v/v) (pH 4). The UV detection was at 298 nm. The quantitation limit both in serum and water was 0.25 micrograms/ml. The method was validated in serum and aqueous solution over the concentration range 0.25-50 micrograms/ml. The extraction recovery from serum spiked with meropenem was 99.7 +/- 3.4%. The intra- and inter-assay coefficients of variation were below 6%. Stored at -80 degrees C for three months at various concentrations in serum and in aqueous solution, meropenem did not reveal any appreciable degradation. After 24 h, it was also stable at 4 degrees C in serum, aqueous solution and supernatant of extraction but not at room temperature. The stability of the drug was also confirmed in serum after repeated freezing-thawing cycles at -80 degrees C on four consecutive days.

Single-dose pharmacokinetics of ampicillin/sulbactam (2:1) combination after intravenous administration to sheep and goats

The pharmacokinetic behaviour of a combination of ampicillin and sulbactam (2:1) in six sheep and six goats after single intravenous doses of 20 mg kg body weight-1 (13.33 mg kg-1 of ampicillin and 6.67 mg kg-1 of sulbactam) was investigated by using a high-performance liquid chromatographic method for determining plasma concentrations. The objective was to determine whether there are differences between sheep and goats in the disposition kinetics of ampicillin and sulbactam. The plasma concentration-time curves were analysed by compartmental pharmacokinetic and non-compartmental methods. The disposition curves for both drugs were best described by a biexponential equation (two-compartment open model) in both sheep and goats. The mean (SD) elimination half-lives of ampicillin were 0.32 (0.05) h in sheep and 0.32 (0.04) h in goats, and the half-lives of sulbactam were 0.74 (0.10) h and 0.79 (0.18) h in sheep and goats, respectively. The apparent volumes of distribution of ampicillin and sulbactam were similar in the two species. Mean (SD) body clearances of ampicillin were 0.69 (0.07) litre h-1 kg-1 in sheep and 0.72 (0.11) litre h-1 kg-1 in goats, and the body clearances of sulbactam were 0.38 (0.03) and 0.38 (0.07) litre h-1 kg-1 in sheep and goats, respectively. There were no significant differences between any of the pharmacokinetic parameters of ampicillin and sulbactam in the sheep and goats.

Isolation of a Staphylococcus aureus beta-lactamase-dicloxacillin complex and kinetic studies on the reactivation of the enzyme

Exposure of the beta-lactamase from Staphylococcus aureus to the slowly reacting substrates cloxacillin or dicloxacillin results in time-dependent inactivation of the enzyme. Methods for the rapid separation of a beta-lactamase-dicloxacillin complex from excess inhibitor, using centrifuged columns of Sephadex G-25 or DEAE-Sephadex G-25, are described. The enzyme-dicloxacillin complex releases active enzyme, with specific activity identical to that of untreated enzyme, after storage at pH 7.5 at 15 degrees C. Full reactivation was accompanied by the release of 0.8 eq of hydrolyzed dicloxacillin. The complex is stable for up to 40 h when stored at pH 3 at 4 degrees C. The reactivation process, which occurs with first-order kinetics at 15 degrees C and pH values between 4 and 8, displays a pH dependence with apparent pKa's of 4.6 and 8.5, and a limiting value of the reactivation rate constant of 0.022 min-1. Deviation from first-order kinetics at pH 9 is consistent with a competing irreversible inactivation of the enzyme at that pH. This behavior differs substantially from that of the similarly inactivated beta-lactamase I from Bacillus cereus, whose rate of reactivation is independent of pH, but which undergoes irreversible denaturation at acidic pH [A. L. Fink, K. M. Behner, and A. K. Tan (1987) Biochemistry 26, 4248-4258]. Addition of hydroxylamine to the S. aureus beta-lactamase-dicloxacillin, complex stimulates the rate of reactivation by a maximum of 35%. This effect is hyperbolically dependent on the concentration of hydroxylamine with half-maximal stimulation at 2.8 mM. The Km for ampicillin hydrolysis catalyzed by the partially reactivated enzyme is identical to that measured for catalysis by the untreated enzyme. We discuss our observations in relation to models for the transient inhibition process.

Determination of the monocyclic beta-lactam antibiotic carumonam in plasma and urine by ion-pair and ion-suppression reversed-phase high-performance liquid chromatography

A sensitive and selective high-performance liquid chromatography method has been developed for the determination of the new monocyclic beta-lactam antibiotic carumonam in plasma and urine. The method for plasma involves protein precipitation with acetonitrile and removal of lipids with dichloromethane; urine is diluted with buffer. Separation and quantification are achieved using a mobile phase based on either ion-suppression or ion-pair chromatography on a reversed-phase column with UV detection. The limit of determination is 0.5 micrograms/ml plasma, using a 0.5-ml specimen, and 25 micrograms/ml urine, using a 50-microliter specimen. The inter-assay reproducibility is generally better than 4% when an internal standard is used. Since beta-lactam antibiotics may degrade on storage, close attention must be paid to the stability of these drugs in biological fluids; novel measures to prevent degradation on storage are described. The assay has been successfully applied to the analysis of several thousand samples from pharmacokinetic studies, including a study involving patients with impaired renal function.

Determination of antibiotics and antimicrobial agents in human serum by direct injection onto silica liquid chromatographic columns

Antibiotics and antimicrobial agents are therapeutically monitored by the direct injection of untreated human serum onto silica columns. This simple approach does not lead to rapid column deterioration since the eluents utilized are almost totally aqueous and, consequently, prevent precipitation of the serum protein on the column. Column capacity of the drugs studied varies due to the mutual interaction of the eluent ionic buffer and organic modifiers. The influence of the number of serum injections on column-back pressure, column capacity and quantitative analyses is discussed.

Cefotaxime metabolism by hemolyzed blood: quantitation and inhibition of the deacetylation reaction

The metabolism of cefotaxime (CTX) by hemolyzed blood at different concentrations, time intervals, and temperatures was studied. Cefotaxime and desacetylcefotaxime (DES) levels were quantitated by reverse phase high pressure liquid chromatography. When CTX was added to tubes with 10% hemolysis, CTX/DES levels (micrograms per milliliter) were 123/134, 161/114, and 202/60 at 37 degrees C, room temperature, and 4 degrees C, respectively, after a 1 hr incubation. No reduction in CTX was observed in control experiments (10% blood, no hemolysis) at these temperatures after 1 hr; 200 +/- 23 micrograms/ml CTX; 5 +/- 2 micrograms/ml DES. The disappearance half-life of CTX in 10% hemolyzed blood at 37 degrees C was 45.7 min and at room temperature 84.3 min (p less than 0.001). The addition of the enzyme inhibitors ethylenediaminetetraacetic acid and p-hydroxymercuibenzoate reduced the metabolism of CTX in the presence of 10% hemolysis after 1 hr at 37 degrees C from 41% to 19% with ethylenediaminetetraacetic acid (0.45 mM) and to 0% with p-hydroxymercuibenzoate (10 mM). Our results suggest that for accurate determinations of CTX serum levels, which often have some degree of hemolysis, such specimens should be collected in tubes with ethylenediaminetetraacetic acid or p-hydroxymercuibenzoate and transported at 4 degrees C.

Antibiotic monitoring in body fluids

Analytical procedures recently described for the quantitative determination of antibiotics in body fluids are reviewed. High-performance liquid chromatography (HPLC) and immunoassays appear as an alternative to current microbiological assays. HPLC has been applied to most antibiotics in clinical use and a major part of the review deals with this technique. Attention is given to sample pretreatment, characteristics of chromatography and detection, and limit of sensitivity. Non-isotopic immunoassays have been essentially applied to aminoglycosides and vancomycin and are also reviewed. Advantages and drawbacks of HPLC and immunoassays are presented.

High-performance liquid chromatographic analysis of cefotetan epimers in human plasma and urine

Cefotetan, a new broad-spectrum 7 alpha-methoxycephalosporin antibiotic, was assayed in plasma and urine by means of reversed-phase high-performance liquid chromatography. Commercially available cefotetan exists in two epimeric forms. The procedure described allows the separation and quantitation of both epimers. For the first time a different pharmacokinetic behaviour (t1/2 = 3 h versus 4 h) for each epimer after intravenous injection to healthy volunteers is demonstrated. It is assumed that one epimer is bound to a greater extent to serum proteins and is therefore responsible for the differences observed. As both epimers exhibit similar antibacterial activity, it seems doubtful whether these differences would have clinical significance. Iothalamic acid was determined simultaneously as a marker of kidney function.

Maternal and fetal pharmacokinetics of moxalactam given intrapartum

Two grams of moxalactam was given intravenously to 28 women at high risk for infection following cesarean delivery. After a mean time of 48 minutes from infusion, maternal sera, cord sera, and uterine tissue obtained at delivery had concentrations of moxalactam of 62 micrograms/ml, 22.2 micrograms/ml, and 9.6 micrograms/gm, respectively. The maternal serum half-time was calculated to b e 2.1 hours. R and S epimeric distribution was determined in these sera and tissues, and the mean R/S ratios were 0.95, 0.93, and 1.22 for the three groups, respectively. The significance of these observations is discussed. A new method in which a high-pressure liquid chromatographic assay is used is described, and results are compared to those obtained with the microbiological assay. The high-pressure liquid chromatographic method was found to be quick, accurate, an reproducible.