Prospective Observational Study of Serum Ceftazidime Concentrations in Hemodialysis Patients at the University Hospital of Charleroi, Belgium

Background

In case of severe infections, the first 24h of treatment are critical to limit the severity and the mortality (1). Thus, the antibiotic treatment must be initiated as soon as possible, be efficacious against the causative organism, and reach concentrations in the infected tissues larger than the minimal inhibitory concentration (MIC). In case of sepsis, pharmacokinetic parameters are modified (e.g., increase of the volume of distribution [Vd]), increase [initially] and decrease [later] of the renal clearance), which impacts on the actual concentration and activity of the antibiotic. For most antibiotics, the adaptation of the dosages is performed in a very crude fashion in case of renal failure (5). A first study has demonstrated that the antibiotic doses prescribed in case of sepsis were, in most of the cases, insufficient to obtain a concentration of 4 times or even 1 time the MIC of the causative organism during the desired fractions of the time between two successive administration (70% for ceftazidime) (6). A second study has shown that the doses of antibiotic prescribed in case of sepsis and of renal failure requiring extracorporeal hemofiltration are insufficient (7). Both studies showed also that there is a large interpatient variability in the antibiotic serum concentrations. An additional factor, rarely taken into account, is that only the free fraction of the antibiotic is active (8). Yet, the free fraction is rarely measured.

The use of ceftazidime in first intention probabilistic antibiotherapy in patients undergoing chronic hemodialysis is supported by its broad spectrum of activity against the most frequently observed organisms in this patient population, including Pseudomonas aeruginosa. The low incidence of adverse effects reported for this antibiotic makes it a better choice than ciprofloxacin. Moreover, its rather simple and controllable mode of administration (one intravenous dose administered at the end of the dialysis period) guarantees a better compliance compared to a daily oral antibiotherapy. Ceftazidime shows a low protein binding, and its activity is therefore not expected to be grossly affected in patients compared to what can be measured in vitro in reference media (9). However, mots reported data on ceftazidime protein binding have been obtained on healthy volunteers and the extent of binding of beta-lactams to serum proteins may considerably vary according to the type of subjects (10).

Presently, the recommendations for the dosages of ceftazidime in patients undergoing chronic hemodialysis are based on rather old pharmacokinetic studies assuming a plasma half-life of ceftazidime reduced to 3.3 h during hemodialysis vs. 33.6 h in anuric patients and recommending to administer half of the total daily dose at the end of the hemodialysis (11). But these recommendations do not take into account the progresses made since then in hemodialysis techniques. The international recommendations and those of the US Food and Drug Administration (FDA) recommend to administer 1 g of ceftazidime after each hemodialysis session (12). Different dialysis parameters modulating the level of removal of ceftazidime in modern dialyzers have been studied (13). This showed that the ceftazidime clearance increases with the rate of dialysis fluid flow, the ultrafiltration volume, and the urea clearance. There is a positive correlation between the increase in blood flow and the ceftazidime clearance that, however, is observed only in patients for whom an AN69 membrane was used (14). Another study has examined the impact of the use of membranes with high permeability on the pharmacodynamics of ceftazidime using mathematical modeling. This study led to a recommendation that ceftazidime should be administered at a daily dose of 1 g to obtain a serum trough concentration higher than the MIC of the causative (or suspected) organism during at least 70% of the dosing interval. A dose of 2 g of ceftazidime after each dialysis session was effective for isolates for which the MIC of ceftazidime was not superior to 16 mg/L (14). This study, however, is based on data collected in 1983 and included only 6 patients. Thus, there has been no in vivo study looking as to whether a dose of 1 or 2 g of ceftazidime administered after each dialysis session is sufficient when using contemporary dialysis equipment. Moreover, no measure of the free fraction has been made.

Objectives