Use of antibacterial agents in renal failure

Pharmacokinetic issues for antibiotics in the critically ill patient

OBJECTIVE

To discuss the altered pharmacokinetic properties of selected antibiotics in critically ill patients and to develop basic dose adjustment principles for this patient population.

DATA SOURCES

PubMed, EMBASE, and the Cochrane-Controlled Trial Register.

STUDY SELECTION

Relevant papers that reported pharmacokinetics of selected antibiotic classes in critically ill patients and antibiotic pharmacodynamic properties were reviewed. Antibiotics and/or antibiotic classes reviewed included aminoglycosides, beta-lactams (including carbapenems), glycopeptides, fluoroquinolones, tigecycline, linezolid, lincosamides, and colistin.

DATA SYNTHESIS

Antibiotics can be broadly categorized according to their solubility characteristics which can, in turn, help describe possible altered pharmacokinetics that can be caused by the pathophysiological changes common to critical illness. Hydrophilic antibiotics (e.g., aminoglycosides, beta-lactams, glycopeptides, and colistin) are mostly affected with the pathphysiological changes observed in critically ill patients with increased volumes of distribution and altered drug clearance (related to changes in creatinine clearance). Lipophilic antibiotics (e.g., fluoroquinolones, macrolides, tigecycline, and lincosamides) have lesser volume of distribution alterations, but may develop altered drug clearances. Using antibiotic pharmacodynamic bacterial kill characteristics, altered dosing regimens can be devised that also account for such pharmacokinetic changes.

CONCLUSIONS

Knowledge of antibiotic pharmacodynamic properties and the potential altered antibiotic pharmacokinetics in critically ill patients can allow the intensivist to develop individualized dosing regimens. Specifically, for renally cleared drugs, measured creatinine clearance can be used to drive many dose adjustments. Maximizing clinical outcomes and minimizing antibiotic resistance using individualized doses may be best achieved with therapeutic drug monitoring.

Vascular and cardiac infections in end-stage renal disease

Patients with end-stage renal disease (ESRD) receiving hemodialysis (HD) are vulnerable to intravascular and endocardial infections. These include vascular access infections, vascular stent infections, and bacterial endocarditis. Staphylococcus aureus is the most commonly encountered microorganism in these conditions. Prolonged intravenous antibiotic therapy is often indicated in these infections. Surgical removal of the infected vascular access or stent may be required. Infective endocarditis occurs less frequently in renal transplant recipients than in patients on HD. Although bacterial endocarditis may occur, fungal endocarditis with organisms such as Aspergillus and Candida species occurs with disproportionately high frequency among renal transplant recipients because of immunosuppression. Prolonged intravenous antibiotic or antifungal therapy is indicated, and valve replacement is often necessary.

Optimizing antimicrobial dosing in the critically ill patient

"We know everything about antibiotics except how much to give," Maxwell Finland once stated. Finally, with the proliferation of pharmacodynamics as a science, we are addressing the question of how much to give. We have moved from an era of more or less arbitrary antimicrobial dosage selection toward one characterized by evidence-based optimal dosing strategies. Optimizing antimicrobial therapy in critically ill patients is more than just the selection of a suitable dose for a particular patient. Optimizing therapy also involves the selection of an appropriate single or combination antibiotic regimen that is active against the suspected or documented pathogens at the site(s) of infection. The regimen should offer the fewest potential adverse events, and the duration of therapy should be the shortest possible so as not to encourage resistance. Dosing of the chosen regimen should reflect variables that are often ignored, such as the patient's weight and age. The new continuous renal replacement therapies are commonly used in the critical care unit and must be considered. Finally, the cost of the regimen should be considered, but not only the cost to purchase the chosen antimicrobial agent but the cost to administer it (, the cost of minibags or syringes, intravenous tubing, saline flushes [all multiplied by the number of times per day the drug is given]), and, most importantly, if the patient fails to respond to therapy, the cost necessary to re-treat the patient to bring about a cure. In this review, we discuss some of the principles required to optimize antimicrobial dosing and recently obtained data regarding its application to the critically ill patient.