Continuous infusion tobramycin combined with carbenicillin for infections in cancer patients

Continuous infusion of beta-lactams

PURPOSE OF REVIEW

Continuous infusion of beta-lactam antibiotics is becoming increasingly popular. The background and current clinical evidence are discussed. Tools to apply continuous infusion are analyzed.

RECENT FINDINGS

One randomized controlled trial in an ICU setting and two nonrandomized controlled trials have shown continuous infusion to be more beneficial than intermittent infusion. One randomized controlled trial in chronic obstructive pulmonary disorder patients, however, showed no difference between the two treatments. The stability of most beta-lactams for use during continuous infusion has been documented.

SUMMARY

Killing of bacteria by beta-lactam antibiotics is maximal at around four times the minimum inhibitory concentration in vitro. To ensure an optimal effect when treating severe infections, free unbound concentrations at or above four times the minimum inhibitory concentration should be maintained. Although continuous infusion has been demonstrated to be superior in animal studies, randomized clinical trials have failed to confirm this in humans, primarily because of suboptimal design. A better designed randomized clinical trial, set up as a pilot study, recently demonstrated a favorable outcome with continuous infusion. A major issue during continuous infusion is the stability of the antibiotic, which may limit its application. The calculation of the infusion rate necessary to obtain the desired free drug concentration is relatively straightforward.

Continuous versus intermittent intravenous administration of antibacterials with time-dependent action: a systematic review of pharmacokinetic and pharmacodynamic parameters

We performed a systematic review of randomised clinical trials to evaluate the comparative pharmacokinetic and pharmacodynamic properties of the continuous versus intermittent mode of intravenous administration of various antibacterials. Data were identified from PubMed (January 1950 to January 2005), Current Contents, the Cochrane central register of controlled trials, and references from relevant articles and reviews. Seventeen randomised clinical trials comparing continuous with intermittent intravenous administration of the same antibacterial regimen and examining the pharmacokinetic and pharmacodynamic properties were included in this systematic review. We reviewed data regarding the clinical setting, number of participants, antibacterial agents and dosages used, as well as maximum serum concentration (Cmax), trough serum concentration (Cmin), steady-state or plateau serum concentration (Css), area under the concentration-time curve (AUC), time above the minimum inhibitory concentration (MIC) [T>MIC], AUC: MIC, elimination rate constant, elimination half-life, volume of distribution and systematic clearance. The mean Cmax of the intermittently administered antibacterials was higher compared with Css achieved by the continuous infusion of the same antibacterial in all eligible studies (Cmax was on average 5.5 times higher than Css, range 1.9-11.2). Css was on average 5.8 times higher than the Cmin of the intermittently administered antibacterials (range 1.2-15.6). In three of six studies the length of time that the drug concentration was above the MIC of the responsible pathogens was longer in patients receiving the antibacterials continuously. In conclusion, the reviewed data suggest that the continuous intravenous infusion of antibacterials with time-dependent bacterial killing seems to be superior than the intermittent intravenous administration, from a pharmacodynamic point of view, at least when treating bacteria with high MIC values for the studied antibacterials.

Continuous versus intermittent intravenous administration of antibiotics: a meta-analysis of randomised controlled trials

Intermittent intravenous administration of antibiotics is the first-line approach in the management of severe infections worldwide. However, the potential benefits of alternate modes of administration of antibiotics, including continuous intravenous infusion, deserve further evaluation. We did a meta-analysis of randomised controlled trials comparing continuous intravenous infusion with intermittent intravenous administration of the same antibiotic regimen. Nine randomised controlled trials studying beta-lactams, aminoglycosides, and vancomycin were included. Clinical failure was lower, although without statistical significance, in patients receiving continuous infusion of antibiotics (pooled OR 0.73, 95% CI 0.53-1.01); the difference was statistically significant in a subset of randomised controlled trials that used the same total daily antibiotic dose for both intervention arms (0.70, 0.50-0.98, fixed and random effects models). Regarding mortality and nephrotoxicity, no differences were found (mortality 0.89, 0.48-1.64; nephrotoxicity 0.91, 0.56-1.47). In conclusion, the data suggest that the administration of the same total antibiotic dose by continuous intravenous infusion may be more efficient, with regard to clinical effectiveness, compared with the intermittent mode. In an era of gradually increasing resistance among most pathogens, the potential advantages of continuous intravenous administration of antibiotics on several clinical outcomes should be further investigated.

Clinical importance of polymicrobial bacteremia

Ninety-one episodes of polymicrobial bacteremia and fungemia were compared with 407 unimicrobial episodes to assess differences in the microbiological, epidemiological, and clinical features of the two syndromes. Enterobacteriaceae, nongroup A streptococci, anaerobic bacteria, and pseudomonads were disproportionately common in polymicrobial bacteremia. Polymicrobial episodes were significantly more likely to be hospital-acquired, to emanate from bowel or multiple foci, and to occur in patients with nonhematologic malignancies or multiple underlying diseases. Deaths directly related to sepsis were twofold higher in polymicrobial versus unimicrobial bacteremia. Factors associated with increased mortality in polymicrobial sepsis included age greater than 40 yr; absent or diminished febrile response to sepsis; absolute granulocytopenia; inadequate antimicrobial therapy for all microorganisms isolated; and a primary focus of infection in the bowel, the respiratory tract, an abscess, or an occult site. The occurrence and type of polymicrobial bacteremia can suggest a source of sepsis as well as additional diagnostic and therapeutic maneuvers.

Clinical importance of "breakthrough" bacteremia

Fifty-one episodes of bacteremia and a single episode of fungemia occurred during treatment with seemingly adequate doses of appropriate antibiotics. Clinical findings in these "breakthrough" bacteremias and fungemia were compared with those in 448 non-breakthrough episodes. Breakthrough was more likely to be caused by facultative or aerobic gram-negative rods (e.g., Enterobacteriaceae and Pseudomonas species) than by anaerobes. Of the underlying conditions examined, immunosuppressive doses of glucocorticosteroids, diabetes mellitus, and moderate renal failure were significantly more frequent in patients with breakthrough. A significant association was also observed between an intra-abdominal primary focus of infection (abscesses, biliary tract or bowel infections) and the occurrence of breakthrough. Mortality in breakthrough bacteremia was 61 percent compared with 40 percent in non-breakthrough episodes. The phenomenon of breakthrough bacteremia shows the potential limitations of antibiotic therapy alone.

Gentamicin and tobramycin dosing guidelines: an evaluation

The provision of pharmacokinetic dosing services has become a cornerstone of clinical pharmacy practice in many institutions. As these services expand, more pharmacists will become involved, and the need for a structured, uniform approach to the provision of these services may be necessary. Therefore, this article discusses specific approaches (i.e., guidelines) to the most common clinical conditions that the pharmacist may encounter. The goal is to promote consistent interpretation and application of clinical and kinetic data by the members of our aminoglycoside dosing service. The guidelines provide a structured yet adaptive approach to the clinical use of gentamicin and tobramycin. The major areas of controversy that were encountered in developing these guidelines are discussed, and the guidelines are presented. These guidelines currently are used to standardize our pharmacokinetic dosing service and as a tool for educating new pharmacists to their role and responsibilities as members of the pharmacokinetic consultation team. Additionally, these guidelines are being used as criteria for the assessment of quality assurance in the area of clinical pharmacokinetics.

Reappraisal of guidelines for pharmacokinetic monitoring of aminoglycosides

The rationale for pharmacokinetic monitoring of aminoglycosides is critically reviewed. Retrospective studies suggest that for optimal antibacterial effect, peak serum gentamicin concentrations should exceed 5 micrograms/ml, despite the fact that these concentrations are indirect measures of the concentration of drug at the site of infection. When quantitative results of antimicrobial susceptibility are known (e.g. MIC or MBC), limited data suggest that for most infections, the peak serum aminoglycoside concentration should exceed the minimum inhibitory concentration by four-fold. However, the optimal duration for which the serum concentration should exceed the MIC or MBC during each dosing interval and the detrimental effect of prolonged subinhibitory drug concentrations have not been evaluated. Furthermore, the immunological competence of the host and the pathogenicity of the infecting organism are important factors in achieving antibacterial response. Using serum creatinine as an indirect and relatively late indicator of nephrotoxicity, nadir gentamicin concentrations greater than 2 micrograms/ml may predispose patients to develop nephrotoxicity. In addition, recent information indicates that patients who accumulate excessive amounts of aminoglycosides in their tissues may be at higher risk for developing nephrotoxicity; these patients may be identified based on the extent of accumulation in their nadir concentrations with continuous dosing. The aminoglycosides diffuse into the inner ear fluids slowly and diffuse out with a half-life of decline in inner ear fluid concentrations slower than that in serum. High transient peak serum concentrations probably do not contribute significantly to the risk of ototoxicity. However, there is evidence from early clinical trials, studies using continuous infusions of aminoglycosides, and animal studies indicating that elevated nadir serum concentrations relate to the development of ototoxicity. There is considerable interpatient variability in the peak serum concentration, even when identical dosages based on body weight or surface area are administered. Similarly, the half-life for decline in serum concentrations is highly variable from patient to patient, even in patients with stable normal renal function. Absorption after intramuscular administration is reliable in most patients, although critically ill patients may experience erratic absorption. The distribution of aminoglycosides is altered in obese patients because of differences in extracellular fluid content between fat and other tissues.(ABSTRACT TRUNCATED AT 400 WORDS)