European harmonization of MIC breakpoints for antimicrobial susceptibility testing of bacteria.
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Anti-Bacterial Agents↗
Biomedical subjects
Johan W Mouton
Publications and source records attributed to Johan W Mouton.
Evaluation of the post-antifungal effect (PAFE) of amphotericin B and nystatin against 30 zygomycetes using two different media.
The post-antifungal effect (PAFE) of amphotericin B and nystatin against 30 clinical zygomycetes was evaluated using two different media. PAFE is a suppression of fungal growth after limited drug exposure. The MICs of both drugs were determined using NCCLS M38-P guidelines. A spectrophotometric method was used to determine PAFE in vitro. Spores were exposed to amphotericin B and nystatin in RPMI-1640 or AM3 at concentrations of 4 x and 1 x MIC for 4 h for Absidia sp. and at 1 x and 0.5 x MIC for 1 h for the other strains. Drugs were eliminated by washing. Exposed and control spores were cultured in microtitre wells and incubated for 48 h. PAFE was calculated as T - C (Delta t) between the control and the exposure fungi. The first increase in optical density (OD0) was used to calculate PAFE and was considered significant when the value of the lower 95%CI of the exposed strain was greater than the upper 95%CI of the control. MIC ranges in RPMI-1640 were: 0.06-4 mg/L for amphotericin B and 0.5-8 mg/L for nystatin; MIC ranges in AM3 were: 0.06-2 mg/L for amphotericin B and 0.5-4 mg/L for nystatin. Killing was not observed at the concentration and exposure time used. In RPMI-1640, for amphotericin B the rank order for PAFE was Absidia corymbifera (5.6 h) > Rhizopus oryzae (5.2 h) > Mucor spp. (3.5 h) > Rhizopus microsporus (3 h), and for nystatin the rank order was Mucor spp. (5.8 h) > R. oryzae (3.3 h) > A. corymbifera (2.9 h) > R. microsporus (1.7 h). PAFE was not induced in Rhizomucor spp. PAFE was dependent on drug concentration.
Amphotericin B↗
In vitro susceptibilities of zygomycetes to conventional and new antifungals.
In vitro susceptibilities of 36 zygomycete isolates, belonging to six genera, to itraconazole, posaconazole, voriconazole, terbinafine, amphotericin B and 5-fluorocytosine were determined by using a broth microdilution adaptation of the National Committee for Clinical Laboratory Standards M-38P reference method. The influence of incubation time on MIC values, and the performance of a spectrophotometric method for MIC determination in comparison with the visual reference method, were also evaluated. Amphotericin B was active against most of the isolates. All the isolates were highly resistant to 5-fluorocytosine (MICs > 256 mg/L). Voriconazole was significantly less active than the other drugs with an overall MIC(90) (MIC at which 90% of the isolates were inhibited) of 32 mg/L. In contrast, posaconazole showed good activity (MIC(90) 1 mg/L). A wide range of MICs, from 0.03 to > or =32 mg/L, was obtained for itraconazole and terbinafine. Differences in susceptibility between and within genera were noted. Rhizopus spp. were significantly less susceptible to itraconazole, posaconazole, terbinafine and amphotericin B than Absidia spp., and less susceptible than Mucor spp. to amphotericin B. Terbinafine appeared to be more active against Rhizopus microsporus than against Rhizopus oryzae (geometric mean MIC of 0.15 and 64 mg/L, respectively). The activity of the drugs was dependent on the incubation period. A significant increase in MICs was noted between 24 and 48 h of incubation. On the other hand, the two methods used for MIC determination (visual and spectrophotometric readings) showed good agreement. These results suggest that the zygomycetes are a heterogeneous group for antifungal susceptibility. Some of the conventional and new antifungals are effective in vitro; their efficacies in vivo remain to be determined. The spectrophotometric method appears to be a valuable alternative to the visual method for MIC determination for zygomycetes.
Antifungal Agents↗
Thoughts on "Population pharmacokinetics and relationship between demographic and clinical variables and pharmacokinetics of gentamicin in neonates".
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Age Factors↗
In vitro drug interaction modeling of combinations of azoles with terbinafine against clinical Scedosporium prolificans isolates.
The in vitro interaction between terbinafine and the azoles voriconazole, miconazole, and itraconazole against five clinical Scedosporium prolificans isolates after 48 and 72 h of incubation was tested by a microdilution checkerboard (eight-by-twelve) technique. The antifungal effects of the drugs alone and in combination on the fungal biomass as well as on the metabolic activity of fungi were measured using a spectrophotometric method and two colorimetric methods, based on the lowest drug concentrations showed 75 and 50% growth inhibition (MIC-1 and MIC-2, respectively). The nature and the intensity of the interactions were assessed using a nonparametric approach (fractional inhibitory concentration [FIC] index model) and a fully parametric response surface approach (Greco model) of the Loewe additivity (LA) no-interaction theory as well as a nonparametric (Prichard model) and a semiparametric response surface approaches of the Bliss independence (BI) no-interaction theory. Statistically significant synergy was found between each of the three azoles and terbinafine in all cases, although with different intensities. A 27- to 64-fold and 16- to 90-fold reduction of the geometric mean of the azole and terbinafine MICs, respectively, was observed when they were combined, resulting in FIC indices of <1 to 0.02. Using the MIC-1 higher levels of synergy were obtained, which were more consistent between the two incubation periods than using the MIC-2. The strongest synergy among the azoles was found with miconazole using the BI-based models and with voriconazole using the LA-based models. The synergistic effects both on fungal growth and metabolic activity were more potent after 72 h of incubation. Fully parametric approaches in combination with the modified colorimetric method might prove useful for testing the in vitro interaction of antifungal drugs against filamentous fungi.
Antifungal Agents↗
Population pharmacokinetic analysis of nonlinear behavior of piperacillin during intermittent or continuous infusion in patients with cystic fibrosis.
The purpose of this study was to describe the nonlinear pharmacokinetics of piperacillin observed during intermittent infusion and continuous infusion by using a nonparametric population modeling approach. Data were 120 serum piperacillin concentration measurements from eight adult cystic fibrosis (CF) patients. Individual pharmacokinetic parameter estimates during intermittent infusion or continuous infusion were calculated by noncompartmental analysis and with a maximum iterative two-stage Bayesian estimator. To simultaneously describe concentration-time data during intermittent infusion and continuous infusion, nonlinear models were parameterized as two-compartment Michaelis-Menten models. Models were fit to the data with the nonparametric expectation maximization algorithm. The calculations were executed on a remote supercomputer. Nonlinear models were evaluated by log-likelihood estimates, residual plots, and R(2) values, and predictive performance was based on bias (mean weighted error [MWE]) and precision (mean weighted square error [MWSE]). A linear pharmacokinetic model could not describe combined intermittent infusion and continuous infusion data well. A good population model fit to the intermittent infusion and continuous infusion data was obtained with the constructed nonlinear models. Maximum a posteriori probability (MAP) Bayesian R(2) values for the nonlinear models were 0.96 to 0.97. Median parameter estimates for the best nonlinear model were as follows: K(m), 58 +/- 75 mg/liter (mean and standard deviation); V(max), 1,904 +/- 1,009 mg/h; volume of distribution of the central compartment, 14.1 +/- 3.0 liters; k(12), 0.63 +/- 0.41 h(-1); and k(21), 0.37 +/- 0.19 h(-1). The median bias (MWE) and precision (MWSE) values for MAP Bayesian estimation with the Michaelis-Menten model were 0.05 and 4.6 mg/liters, respectively. The developed nonlinear pharmacokinetic models can be used to optimize piperacillin therapy administered via continuous infusion in patients with CF and have distinct advantages over conventional linear models.
Adult↗
The epidemiology of vaginal colonisation with group B streptococci in a sexually transmitted disease clinic.
OBJECTIVE: To determine whether Group B streptococcus (GBS) infection is sexually transmitted and whether colonisation with GBS could be related to vaginal symptoms or signs. STUDY DESIGN: In 432 consecutive female patients visiting a Rotterdam STD clinic a structured sexual and gynaecological history was taken. An extensive search was done for sexually transmitted diseases, bacterial vaginosis and vaginal candidosis. A vaginal swab was taken for bacterial culture. A case-control study was performed on a subset of data. RESULTS: Twelve percent of patients were colonised with GBS. No significant correlation was found between sexual behaviour variables and GBS colonisation. Vaginal colonisation with GBS was not correlated with vaginal signs or symptoms. CONCLUSIONS: In our study, vaginal colonisation with GBS was not correlated with any of the epidemiological variables previously reported. Sexual contact does not seem to be the principal way of transmitting GBS. Our findings confirm the general opinion that vaginal colonisation with GBS usually does not cause any vaginal symptoms.
Adult↗
Why the AUC/MIC ratio should not be used to predict the effects of beta-lactams.
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Anti-Bacterial Agents↗
Breakpoints: current practice and future perspectives.
Much of the discussion over the past decades on the value and setting of breakpoints has been due to the fact that the breakpoint was used in two ways; as an indicator to predict the probability of clinical success and also to detect resistant (sub) populations. It is apparent that these two meanings have lead to a different approach to setting, interpretation and use of breakpoints based on clinical efficacy on the one hand and breakpoints based on detection of resistance on the other. Nevertheless, several of the current guidelines make no perceptible distinction between these two meanings. A case is therefore strongly made to recognize that there is a difference between clinical and microbiological breakpoints. The microbiological breakpoint may be used to detect organisms that do not belong to the natural bacterial population, but somehow have acquired resistance and might be useful in recognizing emergence of resistant subpopulations and may lead to subsequent measures to be taken. Alternatively, the clinical breakpoint is of principal value to the clinician in that it results in a classification of S (susceptible), I (intermediate susceptible) and R (resistant) and is used in clinical practice and correlate with a measure of clinical efficacy. Methods developed during the last few years to arrive at meaningful clinical breakpoints are discussed, such as CART analysis and Monte Carlo simulation. In discussing future developments, it is suggested that current reports containing S, I, and R be at least supplemented with the MICs measured and, using current techniques available such as Monte Carlo simulation, provide the probability of successful eradication of the micro-organism and successful treatment based on population pharmacokinetics and Minimal Inhibitory Concentration (MIC) distributions.
Anti-Infective Agents↗
Standardization of pharmacokinetic/pharmacodynamic (PK/PD) terminology for anti-infective drugs.
Over the last decades, the interest in the relationships between the pharmacokinetics (PK) and pharmacodynamics (PD) of antimicrobial agents has increased and, therefore, the use of PK/PD indices and expressions has spread widely. The appropriate definition and use of these parameters is a matter of controversy. This paper contains a proposal to use PK/PD expressions for antimicrobial agents and their units in a uniform manner.
Anti-Infective Agents↗
Extended-interval dosing of tobramycin in neonates: implications for therapeutic drug monitoring.
OBJECTIVE: Our objective was to individualize tobramycin dosing regimens in neonates of various gestational ages with use of early therapeutic drug monitoring. METHODS: This study was performed in neonatal patients with suspected septicemia in the first week of life. All patients received tobramycin, 4 mg/kg per dose, as a 30-minute intravenous infusion, with a gestational age-related initial interval of 48 hours (<32 weeks), 36 hours (32-36 weeks), and 24 hours (> or =37 weeks). The target serum peak and trough serum concentrations were 5 to 10 mg/L and 0.5 mg/L, respectively. Serum trough samples and 1- and 6-hour samples were taken after the first dose. Tobramycin concentrations were used to obtain gestational age-dependent population models with nonparametric expectation maximization software. To investigate the effect of timing of sampling in a second group of patients, serum trough samples and 3- and 8-hour samples were taken after the first dose of tobramycin was administered. Serum trough concentrations were predicted by use of linear pharmacokinetics in both groups and by use of the population models with bayesian feedback of 1 or 2 serum concentrations in the second group. These predicted concentrations were compared with actual serum trough concentrations. The predictive performance of the 1- to 6-hour and 3- to 8-hour models and the population models were compared with a gestational age-related model without therapeutic drug monitoring. RESULTS: A total of 247 patients were analyzed: 206 with 1- to 6-hour serum samples and 41 with 3- to 8-hour serum samples. Peak serum concentrations were above 5 mg/L in 90.8% of cases, and trough serum concentrations were above 1 mg/L in 25.5% of cases. The 3- to 8-hour linear model had a bias of -0.31 mg/L and a precision of 0.48 mg/L, and it performed significantly better than the 1- to 6-hour model. The best nonparametric expectation maximization model had a bias of -0.11 mg/L and a precision of 0.45 mg/L. None of the models yielded a significant improvement of predictive performance over the model without therapeutic drug monitoring. CONCLUSIONS: Routine early therapeutic drug monitoring does not improve the model-based prediction of initial tobramycin dosing intervals in neonates in the first week of life.
Anti-Bacterial Agents↗
In vitro susceptibilities of Zygomycota to polyenes.
The in vitro activity of polyenes was determined for 36 isolates of Zygomycota including Rhizopus spp. (15), Absidia corymbifera (10), Mucor spp. (6), Rhizomucor spp. (3), Cunninghamella bertholletiae (1) and Apophysomyces elegans (1). All isolates were tested with amphotericin B, heated amphotericin B and nystatin by a broth microdilution test. There were no significant differences between heated and unheated solutions of amphotericin B in terms of their antifungal activities. The MICs of amphotericin B for most of the strains were <2 mg/L. For all isolates, nystatin was significantly less active than amphotericin B (P < 0.001). The one C. bertholletiae and one A. elegans isolates were less susceptible to amphotericin B (MICs 2 mg/L) and were also less susceptible to nystatin.
Amphotericin B↗
In vitro activities of new and conventional antifungal agents against clinical Scedosporium isolates.
The susceptibilities of 13 clinical isolates of Scedosporium apiospermum and 55 clinical isolates of S. prolificans to new and conventional drugs belonging to three different classes of antifungal agents, the azoles (miconazole, itraconazole, voriconazole, UR-9825, posaconazole), the polyenes (amphotericin B, nystatin and liposomal nystatin), and allylamines (terbinafine), were studied by use of proposed standard M38-P of NCCLS. Low growth-inhibitory antifungal activities were found in vitro for most of the drugs tested against S. prolificans isolates, with the MICs at which 90% of isolates are inhibited (MIC(90)s) being >8 microg/ml; the MIC(90)s of voriconazole and UR-9825, however, were 4 microg/ml. S. apiospermum isolates were more susceptible in vitro, with the highest activity exhibited by voriconazole (MIC(90)s, 0.5 microg/ml), followed by miconazole (MIC(90)s, 1 microg/ml), UR-9825 and posaconazole (MIC(90)s, 2 microg/ml), and itraconazole (MIC(90)s, 4 microg/ml). The MICs of terbinafine, amphotericin B, and the two formulations of nystatin (for which no statistically significant differences in antifungal activities were found for the two species) for S. apiospermum isolates were high. Cross-resistance was observed among all the azoles except posaconazole and among all the polyenes except the lipid formulation. A distribution analysis was performed with the MICs of each drug and for each species. Bimodal and skewed MIC distributions were obtained, and cutoffs indicating the borders of different MIC subpopulations of the distributions were determined on the basis of the normal plot technique. These cutoffs were in many cases reproducible between 48 and 72 h.
Antifungal Agents↗
Effect of a single percutaneous abscess drainage puncture and imipenem therapy, alone or in combination, in treatment of mixed-infection abscesses in mice.
The importance of supplementary imipenem therapy after a single percutaneous abscess drainage puncture was studied in a mouse model of established mixed-infection abscesses. Animals were treated for 3 days with daily dosing regimens of 384 to 1,536 mg/kg of body weight that took into account the short half-life of this antibiotic in mice. Imipenem therapy in conjunction with abscess drainage was significantly better than drainage alone in reducing the Escherichia coli and Bacteroides fragilis counts in the mixed infections. Furthermore, the killing of B. fragilis by the combination of imipenem therapy and abscess drainage was significantly better than that by imipenem treatment alone. The maximum reductions in E. coli and B. fragilis counts were 1.1 and 2.2 log(10) CFU/abscess, respectively. In contrast, the in vitro activity of imipenem was significantly better (maximum reduction, > or =6.2 log(10) CFU/ml) against mixed cultures of the same strains even when bacterial numbers similar to those found in the abscesses were used. Comparable in vivo activity was achieved only when treatment was started 30 min before inoculation (reduction for both strains, > or =6.1 log(10) CFU/abscess), but this killing was significantly diminished if the start of treatment was delayed until > or =12 h after inoculation. Imipenem concentrations in abscess tissue reached levels above the MIC for E. coli for >60% of the dosing interval. Possible reasons for the reduced activity of imipenem in vivo are discussed, and we conclude that standard susceptibility tests overestimate the efficacy of this antibiotic against the organisms present in these abscesses.
Abscess↗
Efficacy of antifungal therapy in a nonneutropenic murine model of zygomycosis.
Three isolates of zygomycetes belonging to three different genera (Rhizopus microsporus, Absidia corymbifera, and Apophysomyces elegans) were used to produce a disseminated infection in nonimmunocompromised mice. The therapeutic efficacy of amphotericin B, given intraperitoneally at doses ranging from 0.5 to 4.5 mg/kg of body weight/day, oral itraconazole at 100 mg/kg/day, and oral terbinafine at 150 mg/kg/day was evaluated in this model. The markers of antifungal efficacy were the median survival time, the mortality rate, and the percentage of infected organs. Organ culture was performed along with microscopic direct examinations of tissues to assess the presence of an active infection. An acute and lethal infection was obtained in untreated mice challenged with each of the three strains. The data obtained for direct examinations and qualitative cultures indicate that, due to the nonseptate nature of the hyphae, each technique gives different information and should be used together with the others. Against all three strains, amphotericin B yielded a 90 to 100% survival rate. Itraconazole was inactive against R. microsporus but significantly reduced mortality in mice infected with A. corymbifera or A. elegans. Terbinafine had no beneficial effects against R. microsporus and A. corymbifera despite documented absorption of the drug. Overall, only limited correlations were observed between MICs determined in vitro and in vivo efficacy of the drugs. The efficacy of itraconazole in these models of zygomycosis suggests that this drug, as well as the new azole compounds presently under development, warrants close evaluation.
Absidia↗
Method for measuring postantifungal effect in Aspergillus species.
An in vitro method for determination of postantifungal effect (PAFE) in molds was developed by using three isolates each of Aspergillus fumigatus, A. flavus, A. terreus, A. nidulans, and A. ustus. MICs of amphotericin B and itraconazole were determined by using National Committee for Clinical Laboratory Standards guidelines (M38-P). The inoculum was prepared in RPMI 1640 broth buffered with MOPS (morpholinepropanesulfonic acid) at pH 7.0, and conidia were exposed to amphotericin B and itraconazole at concentrations of 4, 1, and 0.25 times the MIC, each for 4, 2, and 1 h at 37 degrees C. The same procedure was followed for controls with drug-free medium. Following exposure, the conidia were washed three times in saline and the numbers of CFU per milliliter were determined. Exposed and control conidia were then inoculated into microtitration plates and incubated at 37 degrees C for 48 h in a spectrophotometer reader. The optical density (OD) was measured automatically at 10-min intervals, resulting in growth curves. PAFE was quantified by comparing three arbitrary points in the control growth curve, the first increase of OD and the points when 20 and 50% of the maximal growth were reached, with the growth curve of drug-exposed conidia. Amphotericin B induced PAFE in A. fumigatus at four times the MIC after 2 and 4 h of exposure ranging from 1.83 to 6.00 h and 9.33 to 10.80 h, respectively. Significantly shorter PAFEs or lack of PAFE was observed for A. terreus, A. ustus, and A. nidulans. Itraconazole did not induce measurable PAFE in the Aspergillus isolates at any concentration or exposure time tested. Further studies are warranted to investigate the implications of PAFE in relation to clinical efficacy and dosing frequency.
Amphotericin B↗
In vitro activities of pentamidine, pyrimethamine, trimethoprim, and sulfonamides against Aspergillus species.
The susceptibilities of 70 strains of Aspergillus species were tested against seven different sulfa drugs and pentamidine by a microdilution method with RPMI 1640 and yeast nitrogen base media. Sulfamethoxazole, sulfadiazine, and pentamidine were active in vitro. The MICs obtained with RPMI 1640 were significantly higher than those with yeast nitrogen base. More studies are needed to further elucidate the action of these drugs.
Anti-Infective Agents↗
Ciprofloxacin in polyethylene glycol-coated liposomes: efficacy in rat models of acute or chronic Pseudomonas aeruginosa infection.
In a previous study in experimental Klebsiella pneumoniae pneumonia, the therapeutic potential of ciprofloxacin was significantly improved by encapsulation in polyethylene glycol-coated ("pegylated") long-circulating (STEALTH) liposomes. Pegylated liposomal ciprofloxacin in high doses was nontoxic and resulted in relatively high and sustained ciprofloxacin concentrations in blood and tissues, and hence an increase in the area under the plasma concentration-time curve (AUC). These data correspond to data from animal and clinical studies showing that for fluoroquinolones the AUC/MIC ratio is associated with favorable outcome in serious infections. Clinical failures and the development of resistance are observed for marginally susceptible organisms like Pseudomonas aeruginosa and for which sufficient AUC/MIC ratios cannot be achieved. In the present study the therapeutic efficacy of pegylated liposomal ciprofloxacin was investigated in two rat models of Pseudomonas aeruginosa pneumonia. In the acute model pneumonia developed progressively, resulting in a rapid onset of septicemia and a high mortality rate. Ciprofloxacin twice daily for 7 days was not effective at doses at or below the maximum tolerated dose (MTD). However, pegylated liposomal ciprofloxacin either at high dosage or given at low dosage in combination with free ciprofloxacin on the first day of treatment was fully effective (100% survival). Obviously, prolonged concentrations of ciprofloxacin in blood prevented death of the animals due to early-stage septicemia in this acute infection. However, bacterial eradication from the left lung was not effected. In the chronic model, pneumonia was characterized by bacterial persistence in the lung without bacteremia, and no signs of morbidity or mortality were observed. Ciprofloxacin administered for 7 days at the MTD twice daily resulted in killing of more than 99% of bacteria in the lung; this result can also be achieved with pegylated liposomal ciprofloxacin given once daily. Complete bacterial eradication is never observed.
Acute Disease↗