Sensitivity testing of enterococci to ciprofloxacin

Penetration of meropenem and cefepim into pancreatic tissue during the course of experimental acute pancreatitis

INTRODUCTION

Recent data from experimental and clinical studies suggest that the antibiotics showing good penetration into the pancreas may reduce mortality by preventing pancreatic infection, which is the most important prognostic factor in acute pancreatitis.

AIM

To determine and compare pancreatic tissue concentrations of meropenem and cefepime at different stages of acute necrotizing pancreatitis in an animal model that has been shown to closely mimic severe human pancreatitis.

METHODOLOGY

Acute necrotizing pancreatitis was induced in rats by a standardized intraductal infusion of glycodeoxycholic acid and intravenous cerulein. Six hours (n = 30) and 48 hours (n = 30) after induction of pancreatitis, the rats were randomized to receive an intravenous 20 mg/kg injection of either meropenem or cefepime. Blood and the head of the pancreas were collected for determining antibiotic concentrations by high-performance liquid chromatography.

RESULTS

Meropenem concentrations in the pancreas at 6 hours of acute pancreatitis increased significantly and decreased at 48 hours of the disease, but were still higher than that in controls. Concentrations of cefepime in necrotic pancreatic tissue were significantly low either during the initial or later phase, but lower in latter, in which the necrosis was more evident. Tissue/serum concentration ratios of meropenem were significantly higher than those of cefepime. However, tissue concentrations of both antibiotics are much higher than the minimum inhibitory concentration values for the common microorganisms involved in pancreatic infections.

CONCLUSION

Although both antibiotics penetrate into the necrotic tissue in sufficient therapeutic concentrations, penetration of meropenem is much better than cefepime. However, good tissue penetration may not solely indicate efficacy of that antibiotic. Therefore, further experimental and clinical studies are needed to determine the therapeutic and prognostic efficacy of these agents.

Determination of meropenem in plasma by high-performance liquid chromatography and a microbiological method

A rapid and selective high-performance liquid chromatographic (HPLC) method for the quantitative determination of meropenem in plasma is described. The drug was separated from plasma after plasma protein precipitation with 15% of trichloroacetic acid. The mobile phase consisted of acetonitrile-water-glacial acetic acid (21.2, 78 and 0.8% v/v, respectively) delivered at a flow rate of 1.2 ml/min. Meropenem was quantified using ultraviolet detection at 296 nm. Meropenem and the internal standard (pheniramine) were well separated from plasma components. The drug could be assayed by the HPLC method in the presence of its analogue, imipenem. The detection limit in plasma was 25 ng/ml of meropenem. The results were compared with those of agar for a microbiological diffusion method using Escherichia coli ATCC 25922 as the test organism. The sensitivity of the microbiological assay was less than 5 ng/ml, but this decreased at higher concentrations. Both methods were applied to the determination of the drug in aqueous solutions and in plasma.

Qualitative analysis of potential metabolites and degradation products of a new antiinfective drug in rat urine, using HPLC with radiochemical detection and HPLC-mass spectrometry

High-performance liquid chromatography (HPLC) was used in combination with radioactivity detection and mass spectrometry (MS) to elucidate the metabolic fate of GV104326, a novel tricyclic beta-lactam antibacterial agent. Metabolic profiles were obtained by analysis of rat urine samples collected after intravenous administration of the 14C-labelled drug at the dose of 50 mg kg-1 (12.95 MBq kg-1). Methods for solid-phase extraction from urine samples and for reversed-phase chromatographic separation of drug related material were developed. HPLC-MS was used to confirm that the parent compound corresponded to the principal peak in the chromatograms, and two minor peaks were identified as potential metabolites of GV104326. They were shown to be an open beta-lactam ring derivative (GV173923) and a dimeric compound (GV196359).

Automated assay for GV104326, a novel tribactam antibiotic, in human plasma by high-performance liquid chromatography and solid-phase extraction

A highly automated, rapid, robust and specific plasma assay for GV104326, a novel tribactam antibiotic, has been developed to monitor human volunteer trials. The method involves automated solid-phase extraction with a strong anion-exchange phase and HPLC on a reversed-phase column with ultraviolet detection. The calibration range for the assay is 0.05-2 micrograms/ml. The assay is linear over this range and is specific with respect to endogenous interference and likely metabolites of GV104326. Both intra- and inter-assay variability were < 8% and intra- and inter-day bias < 10%.

Susceptibility of urinary pathogens in a Dublin teaching hospital

The range and resistance patterns of organisms causing urinary tract infections (UTI) vary with time and place. A prospective study of midstream urine (MSU) specimens, received over a 3 month period, was therefore undertaken. The antibiotic sensitivities of 528 isolates from 196 domiciliary and 332 hospitalised patients with significant bacteriuria (> 10(5) organisms/ml) were determined using the modified Stokes method. Escherichia coli accounted for 79% of domiciliary isolates and 57% in hospitalised patients. Gram positive organisms causing UTI have become increasingly common and were isolated from 8% and 15% of domiciliary and hospitalised patients respectively. Resistance levels for co-amoxiclav (Augmentin) were low (7% domiciliary, 14% hospitalised). However 46 Gram negative isolates (10%) had intermediate sensitivities to co-amoxiclav on disc testing. Breakpoint testing showed 89% of these to be sensitive at the urinary breakpoint but only 52% were sensitive at the systemic breakpoint. Forty nine percent of E. coli from hospital specimens were resistant to pipercillin, due to TEM-1 beta lactamase production. A 6% resistance level to ciprofloxacin in domiciliary E. coli is considerably higher than previous reports and gives cause for concern. Gentamicin resistance was found in 4% of Gram negative hospital isolates, a finding of some significance in the empiric treatment of septicaemia of urinary tract origin.

The fluoroquinolones exert a reduced rate of kill against Enterococcus faecalis

The bactericidal activities of ciprofloxacin, ofloxacin and DR-3355 have been investigated against Enterococcus faecalis, Staphylococcus aureus and Staphylococcus epidermidis over 24 h. The three fluoroquinolones were found to be rapidly bactericidal against the staphylococci, killing over 99% of the bacteria during the first 3 h of exposure with a further reduction in viability of approximately one logarithm occurring over the next 21 h. In contrast, the fluoroquinolones displayed a much slower rate of kill against E. faecalis, as little or no bactericidal activity was detected over the first 3 h for both E. faecalis ATCC19433 and a clinical isolate. At 6 h all three of the drugs were bactericidal against the enterococci although the amount of kill was not as great as against the staphylococci. However, at 24 h the amount of kill obtained with all three drugs was similar to that obtained for staphylococci exposed to these drugs. Ciprofloxacin, ofloxacin and DR-3355 were not active against E. faecalis ATCC19433 in phosphate buffered saline and therefore require cell division for their bactericidal activity against this species.

Susceptibility of bacterial isolates from AIDS patients to six fluoroquinolones

The susceptibilities to ciprofloxacin, DR-3355 (S-(-)-ofloxacin), enoxacin, lomefloxacin, ofloxacin and PD127,391 of 69 significant bacterial isolates from HIV-positive patients at the City Hospital, Edinburgh have been determined. With the exception of the enterococci, most of the strains tested (including staphylococci, Escherichia coli and Pseudomonas aeruginosa) were susceptible to the fluoroquinolones. Ciprofloxacin was the most active of the clinically available drugs followed by ofloxacin, lomefloxacin and enoxacin. PD127,391 and DR-3355, the new fluoroquinolones tested, were at least as active as ciprofloxacin. Hence bacterial infections in AIDS patients should respond to fluoroquinolone therapy.