Optimal adaptive control of pharmacodynamic effects with aminoglycoside antibiotics: a required approach for the future

Development of a Semimechanistic Model to Describe the Pharmacokinetics of Gentamicin in Patients Receiving Hemodialysis

The aim of this study was to ascertain the most suitable dosing schedule for gentamicin in patients receiving hemodialysis. We developed a model to describe the concentration-time course of gentamicin in patients receiving hemodialysis. Using the model, an optimal dosing schedule was evaluated. Various dosing regimens were compared in their ability to achieve maximum concentration (C(max), > or = 8 mg/L) and area under the concentration time-curve (AUC > or = 70 mg x h/L and < or = 120 mg x h/L per 24 hours). The model was evaluated by comparing model predictions against real data collected retrospectively. Simulations from the model confirmed the benefits of predialysis dosing. The mean optimal dose was 230 mg administered immediately before dialysis. The model was found to have good predictive performance when simulated data were compared to data observed in real patients. In summary, a model was developed that describes gentamicin pharmacokinetics in patients receiving hemodialysis. Predialysis dosing provided a superior pharmacokinetic profile than did postdialysis dosing.

Pharmacokinetic and pharmacodynamic parameters of antimicrobials: potential for providing dosing regimens that are less vulnerable to resistance

Whereas infections caused by multidrug-resistant micro-organisms are increasing worldwide, there are few new molecules, especially ones that are active against Gram-negative strains. There are extensive data showing that the administration of antimicrobials according to pharmacokinetic/pharmacodynamic parameters improves the possibility of a positive clinical outcome, particularly in severely ill patients. Evidence is growing that when pharmacokinetic/pharmacodynamic parameters are used to target not only clinical cure but also eradication, the spread of resistance will also be contained. The present paper summarizes the most relevant papers published in this field and provides some suggestions for dosing regimens that can be adopted in the clinical setting to limit the spread of resistance.

Population pharmacokinetics and pharmacodynamics of cefpirome in critically ill patients against Gram-negative bacteria

OBJECTIVES

To develop a population pharmacokinetics model for cefpirome in ICU patients, to assess pharmacokinetic-pharmacodynamic profiles vs. MIC distribution of likely ICU pathogens, and to assess their expected cumulative fraction of response (CFR).

DESIGN AND SETTING

Prospective observational study in a multidisciplinary ICU.

MEASUREMENTS AND RESULTS

Twelve patients received 2g cefpirome intravenously over 12h. Thirteen blood samples were taken on two occasions. Demographic and creatinine clearance data were collected. Based on the final covariate model obtained using NONMEM, Monte Carlo simulations were undertaken to simulate free-drug concentrations for two administration methods: intermittent bolus administration (IBA) and continuous infusion (CI) with a loading dose of 0.5 g. Concentration-time profiles were evaluated by the probability of achieving free-drug concentrations above the MIC for more than 65% of dosing interval. Using MIC distributions from the EUCAST programme the CFR for each method was evaluated. A three-compartment model with zero-order input best described the concentration-time data. The CFR for Escherichia coli and Klebsiella spp. was greater than 97% in all IBA and CI doses but for Pseudomonas aeruginosa, and Acinetobacter spp. achieved target concentrations of 56% and 46%, respectively. High-dose CI cefpirome (6g/day) for P. aeruginosa and Acinetobacter spp. was required to achieve CFR of 89%.

CONCLUSION

Measured creatinine clearance appears to be a good marker of cefpirome clearance and potentially could be used to individualise cefpirome therapy. When given as IBA or CI for E. coli and Klebsiella spp., cefpirome should be successful. Cefpirome fails to achieve the bactericidal target even when administered at high-doses such as 6g/day for P. aeruginosa and Acinetobacter spp. Prospective clinical studies are needed to conclusively validate these findings.

Comparison of faecal and optimal growth conditions on in vitro pharmacodynamic activity of marbofloxacin against Escherichia coli

The objective of the study was to compare the in vitro activity of marbofloxacin against Escherichia coli (E. coli) strains with differing marbofloxacin susceptibility levels under optimal growth conditions and under condition mimicking faecal environment in time-kill kinetic studies. Under optimal growth conditions, marbofloxacin exerted a bactericidal concentration-dependent activity against all E. coli strains with bactericidal concentrations equal to 1 or 4 times MIC. Under faecal growth conditions, marbofloxacin maintained a bactericidal concentration-dependent activity but a 4- to 16-fold increase in bactericidal concentration was required to produce a similar magnitude of effect at 8 h. The bactericidal activity decreased between 8 and 24 h and allowed a residual bacterial population to subsist with a significant regrowth for some of them. Under no-growth conditions, marbofloxacin produced a very low decrease of non-dividing bacteria during a short time. No concentration produced a reduction > or = 3log10 in viable count excepted for two susceptible strains at concentration > or = 64 x MIC after 4 h exposure. The pharmacodynamic parameters from time-kill kinetic studies provide a useful means of studying antimicrobial activity. The importance of using different growth conditions is indicated by the difference in the killing of E. coli in the absence of active dividing cells and in the presence of autoclaved faecal content, both of which have a detrimental effect on the activity of marbofloxacin.

Antibiotic therapy for severe bacterial infections: correlation between the inhibitory quotient and outcome

In severe bacterial infections, treatment failure can occur even when the infecting organism has displayed in vitro susceptibility to the antibiotics used. Several pharmacokinetic-pharmacodynamic parameters show better correlation with therapeutic outcome than susceptibility results. This study was devised to assess the relation between the inhibitory quotient (IQ), i.e., the ratio of achievable antibiotic concentration at the infection site to the minimum inhibitory concentration for the infecting organism, and both clinical and bacteriological outcomes in 290 severe bacterial infections. Multivariate analysis showed that the IQ was a strong predictor of therapeutic outcome ( P< 0.001-0.002): values <4 predicted failure, and those >or=6 cure. This simple parameter could be routinely used to guide effective antibiotic therapy.

Sequential antimicrobial therapy: pharmacokinetic and pharmacodynamic considerations in sequential therapy

The pharmacodynamic factors important in sequential therapy are largely unknown. This is because most pharmacodynamic investigations concentrate on how bacterial populations respond to first antimicrobial exposures. However, it is likely that for B lactams T>MIC and for quinolones the antimicrobial AUC/MIC ratio will be important. Factors which reduce antimicrobial absorption will impact on these parameters and require further study.