Influence of human ascitic fluid on the in vitro antibacterial activity of moxifloxacin.

We investigated the in vitro influence of HAF on the antibacterial activity of moxifloxacin against Escherichia coli ATCC 10798, Escherichia coli K-12, Proteus rettgeri (Sanelli), Staphylococcus aureus ATCC 25923, Staphylococcus aureus NCTC 1808 and Staphylococcus epidermidis ATCC 12228. Human ascitic fluid was obtained from 6 cirrhotic patients by paracentesis. The interaction effect was evaluated by the checkerboard technique. Our results indicate the ability of human ascitic fluid to reduce minimum inhibitory concentrations of moxifloxacin against Gram-negative bacteria, but not against Gram-positives.

Cefazolin concentrations in serum during cardiopulmonary bypass surgery.

The objective of the study was to investigate possible changes in cefazolin serum levels induced by cardiopulmonary bypass (CPB). Six cardiac male patients who underwent cardiac surgery requiring CPB took part in the study. Cefazolin 2 g was intravenously infused over 60 min before anesthesia and blood samples were taken at appropriate times after drug administration (0, 0.25, 0.5, 1, 4, 6, 8 h), 2 min before and 5 min after the beginning and 2 min before and 5 min after the end of CPB. Drug serum concentrations were determined by means of a microbiological method. Five minutes after the start of CPB, cefazolin serum levels decreased on average by 46.6% and remained steadily low until 5 min after the end of CPB. Then, they rose on average by 37.3% at 4 h and then declined slowly until the last sampling at 8 h. Cefazolin serum concentrations were low during CPB but remained in a potentially effective range for antimicrobial prophylaxis for this surgery.

Effects of daily oral administration of rifaximin and neomycin on faecal aerobic flora in rats.

The aim of this study was to compare the influence of rifaximin and neomycin on faecal flora in rats. The study was performed on 18 Wistar rats (three groups of six male animals). Group 1 received rifaximin (50 mg kg(-1)/day), group 2, neomycin (50 mg kg(-1)/day) and group 3 was used as control. Drugs were administered orally, once daily for 3 days. Faecal specimens, collected from each rat on day 3, were cultured for the quantitative and qualitative determination of aerobic microorganisms. Rifaximin treatment produced a marked reduction in the number of total aerobic bacteria and Salmonellae; neomycin caused reduction in Salmonellae, but did not cause statistically significant changes in total aerobic bacterial count. The binding of neomycin with faeces could explain this limited activity, which does not correlate with the in vitro susceptibility of the organism affected. These results confirm that rifaximin is suitable for topical treatment to reduce selected bacterial load in the gut intestines.

In vitro activity of fosfomycin in combination with various antistaphylococcal substances.

Using the chequerboard technique we studied the in vitro activity of the broad spectrum antibiotic fosfomycin in combination with vancomycin, rifampicin, linezolid, quinupristin/ dalfopristin, cefazolin, meropenem and moxifloxacin against two Staphylococcus epidermidis strains (ATCC 12228, DSM 3269) and five Staphylococcus aureus isolates (ATCC 29213, DSM 683, DSM 46320, GISA 323/93, MRSA 3558/00). The phenomena of 'trailing' and 'skipped wells' did not present a problem. Synergy was the most common effect of all drugs tested in combination with fosfomycin; only combination with vancomycin showed antagonism for two of seven isolates. Using a killing-curve technique fosfomycin showed cidal activity, where increasing the drug concentration above the MIC did not enhance killing velocity. Inhibitory concentrations of vancomycin plus fosfomycin against DSM 46320 caused effects identical to those observed with vancomycin alone. The combination of fosfomycin plus linezolid exerted the bacteriostatic effect found with linezolid alone. Fosfomycin plus quinupristin/dalfopristin exhibited the bactericidal effect found with fosfomycin alone (in contrast to the rapidly bactericidal effect of quinupristin/dalfopristin). Electron microscopy showed that fosfomycin given in combination with linezolid, quinupristin/dalfopristin or moxifloxacin (substances that do not cause morphological alterations when given alone) resulted in 'cauliflower-shaped' distortion as caused by fosfomycin alone. Our in vitro data indicate considerable potential for fosfomycin used in combination with other antistaphylococcal antimicrobials, especially linezolid or quinupristin/dalfopristin.

Fleroxacin uptake in ischaemic limb tissue.

Antibiotic application to patients with ischaemia of lower limbs may be indicated to avoid or treat infection of soft tissues. Fleroxacin, a fluoroquinolone, active against various Gram-negative and Gram-positive organisms may be used for this purpose. We evaluated the diffusion of fleroxacin into bone, subcutaneous fat, muscle and tendon tissues of lower limb tissue after a 400 mg i.v. dose. Concentrations in ischaemic tissues were similar to those found in non-ischaemic sites. Since the maximum antibiotic levels found were lower than the MICs of various pathogens relevant for infection, we suggest to increase the dose used for this peri-operative prophylaxis to 800 mg.

Antibacterial activity of gentamicin and ciprofloxacin against Gram-negative bacteria: interactions with pig and calf sera.

The antibacterial activity of pig and calf serum and its ability to interact with gentamicin and ciprofloxacin were studied in vitro using Escherichia coli K-12, Proteus rettgeri (Sanelli) and Klebsiella pneumoniae ATCC 10031. The antimicrobial activity of the above drugs, alone or in combination with serum, was investigated by the checkerboard method and expressed as the minimal inhibitory concentration (microg ml-1). Pig serum (25%) with gentamicin had a synergistic antibacterial effect against Escherichia coli K-12 and pig serum (25%) with ciprofloxacin against Proteus rettgeri (Sanelli) and Klebsiella pneumoniae ATCC 10031. Calf serum (25%) had a synergistic effect with gentamicin against Proteus rettgeri (Sanelli) and calf serum (25%) plus ciprofloxacin against Klebsiella pneumoniae ATCC 10031. The effects of these drugs may be enhanced by pig and calf sera.

Effects of cardio-pulmonary bypass on vancomycin plasma concentration decay.

The objective of the study was to investigate possible changes in vancomycin serum levels induced by cardio-pulmonary bypass (CPB). Ten cardiac patients (seven males, three females, aged between 56 and 81), who underwent cardiac surgery requiring CPB, took part in the study. Vancomycin (15 mg kg-1) was intravenously infused over 60 min before anaesthesia and blood samples were taken at appropriate times after drug administration (0, 0.5, 1, 6, 8 h), after starting CPB (0, 5, 30 and 60 min) and after aortic unclamping (0, 5, 30, 60, 120 min). Drug serum concentrations were determined by means of a fluorescence polarization immunoassay. The area under the concentration-time curve (AUC) measured during CPB were compared with the AUC extrapolated in the same interval by fitting a two-compartment pharmacokinetic model to drug concentrations obtained before and after CPB. Five minutes after starting CPB vancomycin serum levels decreased, on average, by 40.9% and remained steadily lower than the expected values over the next 60 min. In the same interval, the measured AUC was 31.7% lower than the expected AUC. In no instance did serum levels fall below the MIC for most common pathogens (1-2 mg l-1). At aortic unclamping serum levels slightly rebounded but tended to remain lower than the expected concentrations over the next 120 min. In conclusion, during CPB vancomycin serum levels invariably decreased but, at the dose employed (15 mg kg-1), remained in a potentially effective range for antimicrobial prophylaxis.

Antibacterial activity of peritoneal exudate in patients treated with 2 g cefotiam for surgical anti-microbial prophylaxis.

The objective of this study was to investigate the presence of antibacterial activity in peritoneal exudate (PE) of patients treated with cefotiam (CFT). CFT (2 g) was administered as a 'single-shot' antimicrobial prophylaxis to 6 patients at the beginning of colorectal resection. Samples of PE were collected from each patient on days 1, 2 and 3 after surgery. CFT was detectable in the samples of day 1 for 5 of the 6 patients. The influence of PE on antibacterial activity of the antimicrobial drug was evaluated carrying out the MICs of CFT against Escherichia coli K-12, E. coli (ATCC 10798), Klebsiella pneumoniae (ATCC 1003), Proteus rettgeri (Sanelli) and Staphylococcus aureus (ATCC 29213) with and without the addition of PE. The presence of PE enhanced the antimicrobial activity of CFT against gram-negative strains, but not against S. aureus (ATCC 29213). These results suggest the presence of substances in PE that possess endogenous antibacterial activity. Thus, antimicrobial activity in PE cannot be predicted by evaluating pathogen sensitivity in vitro only.

Antibacterial activity of human pleural fluid: alone and in combination with antibiotics.

This study investigated the antibacterial activity of human pleural fluid (HPF) and its interaction with gentamicin (GM), meropenem (MRPM), ciprofloxacin (CPFX) and clarithromycin (CLTM) against Escherichia coli K-12, Proteus rettgeri (Sanelli) and Staphylococcus aureus. Minimal inhibitory concentrations or volumes, expressed as MIC or volume percentage (MIV, V/V%), were measured using a micro-dilution technique in microtiter plates. The antimicrobial activity of HPF combinations with antimicrobial drugs was evaluated by the chequerboard method calculating the fractional inhibitory concentration index (FIC) values. HPF MIVs (%) were: 37.54; 19.85; 1.74 for E. coli, P. rettgeri and S. aureus, respectively. FIC values indicated a synergistic effect with GM, MRPM and CPFX against E. coli and P. rettgeri and an additive effect for the combination HPF plus CLTM or indifference with HPF plus GM and CPFX against S. aureus. The presence of antibodies, complement factors, lysozyme, alpha-defensins and enzymes could explain the antimicrobial activity of HPF and its synergistic effect with certain antibiotics.

Teicoplanin concentrations in serum, pericardium, pericardial fluid and thoracic wall fat in patients undergoing cardio-pulmonary bypass surgery.

The concentrations of teicoplanin in serum, pericardium, pericardial fluid and thoracic wall fat were measured in patients undergoing cardio-pulmonary bypass (CPB) after the administration of a single i.v. 12 mg/kg dose. Five minutes after the start of CPB, teicoplanin serum concentrations decreased by, on average, 35% (95% confidence interval (CI): 28-42%) and remained significantly lower than the expected values over the subsequent 60 min period. After aortic unclamping drug concentrations rebounded but remained significantly lower than the expected values in the next 60 min. Immediately before CPB, penetration of teicoplanin in pericardium and thoracic wall fat was 0.44 (95% CI: 0.23-0.65) and 0.05 (95% CI: 0.03-0.7), respectively, and increased at the end of CPB to 0.90 (95% CI: 0.55-1.25) and 0.17 (95% CI: 0.05-0.29), respectively. MICs for most staphylococcal strains were attained during CPB procedure in pericardium but not in thoracic wall fat. However, since staphylococcal infections involve the interstitial space it is likely that penetration into fat cells is not important for antimicrobial prophylaxis. In this respect, it is worth noting that drug concentration in pericardial fluid, which should reflect the interstitial concentration, was higher than the MIC for most staphylococcal strains. Although no infective complications were observed in our limited series of patients, larger clinical trials are needed to assess whether the dose regimen employed is effective in preventing post-CPB surgery infections.

The in vitro synergistic inhibitory effect of human amniotic fluid and gentamicin on growth of Escherichia coli.

The activity of serum and its synergistic effect with many antibiotics against bacteria are well known. Few reports are available on similar phenomena produced by human amniotic fluid (HAF). Thus we investigated the antibacterial activity of HAF and the presence of a synergistic effect with gentamicin (GM) against Escherichia coli strains. Antimicrobial activity was evaluated as a delay of the growth curve, using a turbidimetric method. E. coli ATCC 10798 and E. coli SC 12155 were employed as test micro-organisms in nutrient broth, and GM was used at a subinhibitory concentration. HAF exerted antibacterial activity and, cooperating with GM at subinhibitory concentration, enhanced its antibiotic activity against E. coli. The presence of Schlievert's glycoprotein in HAF could explain these results.

Effects of cardiopulmonary bypass on teicoplanin serum disposition.

The time course of teicoplanin (T) serum concentrations was determined in 6 patients who had undergone cardiopulmonary bypass (CPB). The drug was given i.v. (12 mg/kg) 85-140 min before starting CPB. Serum concentrations of T were measured with an automated fluorescence polarization immunoassay, at appropriate times before, during and after CPB (total sampling interval: 12 h). Five min after initiating CPB, T serum concentrations decreased, on average, by 29% and remained less than the expected values (values extrapolated from the decay curve, measured excluding the CPB period) over the subsequent 60 min. When CPB was discontinued, the T serum concentrations rebounded to the expected values within 5 min. The mean area under the curve (AUC) during CPB was significantly lower than the mean extrapolated AUC. It was concluded that CPB reversibly reduced T serum concentrations, probably due to drug redistribution. Nevertheless, T serum levels were always above the mean inhibitory concentration (MIC) of the most common pathogenic organisms associated with CPB surgery infections.

Collagen shields delivery of netilmicin: a study of ocular pharmacokinetics.

Collagen shields have been used as therapeutic contact lenses to promote corneal epithelial healing and to deliver hydrosoluble drugs. In albino rabbits, we studied the ocular pharmacokinetics of netilmicin, an aminoglycoside antibiotic, released by a 24-hour collagen shield immersed for 10 min in commercially available eye solution of netilmicin, at the standard concentration of 3 mg/ml. The animals were sacrificed after 0.5, 1, 6 and 18 h. The antibiotic concentrations were measured by the microbiological method. The drug levels remained above the MIC for the usual pathogens for 18 h in the cornea and for 6 h in the aqueous humor. In the iris and ciliary body the peak concentration was reached 1 h after shield application, netilmicin concentration decreased thereafter rapidly. The lens and the vitreous did not appear to be permeated by the drug. In the conjunctiva, drug concentrations were low, showing a negligible lateral diffusion of netilmicin released by shields. In conclusion, our findings show, that if the collagen shields are used as delivery systems, a very concentrated drug solution is not required to obtain high and persistent levels of netilmicin in cornea.

Study on the bactericidal activity and synergistic effect of neutropenic rat serum with gentamicin.

It is well known that normal rat serum (NRS) shows an antibacterial activity because of the presence of endogenous substances that are able to express a defence against pathogenic microorganisms. Moreover, in former studies, we observed that NRS presents a synergistic activity with some antibiotics (thus able to lower minimum inhibitory concentration values). The aim of this research was to study the antibacterial activity and synergistic effect of neutropenic rat sera (NPRS) with gentamicin. The animals were made neutropenic by the i.p. injection of cyclophosphamide (100 mg/kg on day 0 and 75 mg on day 4). At all tested concentrations (from 0.25% to 5%) NPRS showed lower antibacterial activity than NRS with differences which were always statistically significant. The synergistic activity of NPRS with gentamicin was still present and quite similar to that of NRS, in spite of many altered blood parameters showing evident immunodepression. Some possible interpretations of these results are discussed.

Penetration of carumonam into the pleural fluid: comparison of intravenous bolus and constant infusion in rats with experimentally induced pleurisy.

The penetration of carumonam into the pleural exudate of rats was compared after intravenous administration of 30 mg kg(-1) of the drug as a bolus dose or by continuous infusion over 60 min. Both methods of administration ensured a good penetration of carumonam in pleural exudate, as measured by the areas under the concentration-time curves (AUC). The mean values of the ratio of AUC in exudate to AUC in serum (1.07 +/- 0.11 and 0.96 +/- 0.13 for bolus injection and continuous infusion, respectively) were not significantly different. Administration as a bolus dose resulted in significantly higher peak concentrations in pleural exudate as well as in shorter peak times, whereas continuous infusion produced carumonam levels above the MIC for consistently longer times. The pharmacokinetic parameters obtained by analysis of serum carumonam concentrations proved to be independent of the mode of administration. The foregoing results suggest that carumonam may constitute an effective therapeutic alternative to existing antibiotics for the treatment of pleurisy caused by susceptible organisms. No clear superiority of either method of administration could be established on the basis of pharmacokinetic data.

Comparison of the antibacterial activity and synergistic activity towards antibiotics of different mammalian sera.

The antibacterial activity against Escherichia coli ATCC 10798 and Staphylococcus aureus Mag 90 of normal sera from nine species of mammals was investigated by Avantage (Abbott). Human and rat sera showed the highest antibacterial activity against E. coli ATCC 10798, while all investigated sera did not exhibit, till the maximum concentration tested (20%), spontaneous antibacterial activity against S. aureus Mag 90. Heat inactivated sera (56 degrees C for 30 min) of all investigated species lost their antibacterial activity, but maintained their synergistic effect with sub-MICs of some antibacterial drugs, principally against E. coli ATCC 10798.

Possible influence of assay methods in studies of the pharmacokinetics of antibiotics.

In the present research, levels of gentamicin (GM) in serum and carrageenan pleural exudate from the rat have been compared, using three evaluation methods: microbiological assay (MA), enzyme-immunoassay (EMIT) and fluorescence-immunoassay (TDX). In a first study, the evaluations carried out by MA and EMIT have furnished comparable data in serum, while statistically significant differences were verified at all times in pleural exudate. On the contrary, in a second study, while the evaluations carried out by MA and EMIT, at all times and in both biological fluids, have produced similar data, the evaluation carried out by TDX consistently supplied higher results, with statistically significant differences at some times (5 min and 60 min for serum, 30 min and 60 min for exudate). Some possible interpretations of these results are discussed.

Oral disposition kinetics of ofloxacin in patients with compensated liver cirrhosis.

The disposition kinetics of ofloxacin, a quinolone antibacterial agent excreted essentially unmodified by the kidney, was studied after single oral administration in 8 patients with compensated liver cirrhosis and in 8 control subjects. Mean elimination half-life and apparent volume of distribution were significantly increased in the cirrhotic group (7.6 vs. 4.9 h and 1.6 vs. 1.2 liters kg-1, respectively). A reduction in the renal clearance of ofloxacin was also observed in the cirrhotic patients, in spite of an apparently normal renal function. These observations indicate that also the pharmacokinetics of unmetabolized drugs may be altered in compensated liver cirrhosis. The serum concentration-time profiles of nearly all subjects exhibited a secondary peak 4-6 h after dosing. This double-peak behavior was interpreted as either enterohepatic circulation or biphasic gastric emptying of ofloxacin.

Influence of the mode of intravenous administration on the penetration of ceftazidime into tissues and pleural exudate of rats.

The influence of the mode of intravenous (i.v.) administration (bolus injection or continuous infusion) on the tissue penetration of ceftazidime was studied in the rat. The antibiotic concentration was monitored in serum, pleural exudate, vitreous humor, kidney, liver, lung, testicles and epididymal fat tissue. Administration as a bolus resulted in a significantly higher AUC in pleural exudate and in higher peak levels in serum, liver and lung than continuous infusion, which produced a higher peak concentration in kidney than a bolus. No differences in AUC and peak concentrations between the two methods of administration were observed in the other tissues or fluids. With either method of administration the highest antibiotic accumulation was observed in kidney.