Choosing between the new cephalosporin antibiotics: a pharmacodynamic approach

Cefazolin bolus and continuous administration for elective cardiac surgery: improved pharmacokinetic and pharmacodynamic parameters

OBJECTIVE

Cefazolin (1-2 g bolus at induction possibly repeated after cardiopulmonary bypass) remains the standard for antibiotic prophylaxis in cardiac surgery. Data indicate, however, that it is underdosed with this dosing schedule. A prospective, randomized study comparing intermittent versus loading dose plus continuous infusion for the same total dose of cefazolin was performed to assess which modality is pharmacokinetically and pharmacodynamically advantageous.

METHODS

Patients received 2 g cefazolin as a starting dose and then were divided into an intermittent group (receiving another 1 g at 3, 9, and 15 hours after the first dose) and a continuous group (continuous infusion started after the first dose, providing 1 g every 6 hours for 18 hours). Cefazolin levels were measured in blood and atria.

RESULTS

Mean total and calculated free trough concentrations in blood varied greatly among patients in the intermittent group and were lower than those in the continuous group (P < .05 at 15, 18 and 24 hours). For 9 of 10 (90%) patients in the continuous infusion group, the targeted pharmacokinetic and pharmacodynamic goal (time above minimal inhibitory concentration >90%) was achieved, whereas the goal was met for only 3 of 10 (30%) in the intermittent group (P < .05). The mean atrial tissue concentration was also higher with continuous infusion (P < .05).

CONCLUSIONS

Administration of cefazolin as bolus plus continuous infusion has pharmacokinetic and pharmacodynamic advantages relative to intermittent administration. It provides more stable serum levels, lower interpatient variability, and higher myocardial tissue penetration.

Continuous infusion of ceftazidime in the empiric treatment of febrile neutropenic children with cancer

PURPOSE

Infection remains one of the most important complications in cancer therapy. The choice of antibiotics and the method of administration can affect results. Beta-lactam antibiotics can be administered by several short injections per day or by continuous infusion. The latter modality may provide superior pharmacokinetics.

PATIENTS AND METHODS

The authors studied the pharmacokinetics of ceftazidime in children treated for malignancy and in febrile aplasia after chemotherapy. They received a continuous infusion of ceftazidime (200 mg/kg/day) after a loading dose (65 mg/kg/day) administered with amikacin (25 mg/kg/day) and vancomycin (50 mg/kg/day). RESULTS Twenty-three pharmacokinetic studies were performed. Mean ceftazidime serum levels were 31.1 +/- 11.9, 31.2 +/- 10, 32.4 +/- 11.6, 33 +/- 11.6, and 30.4 +/- 12.1 mg/L at 25, 27, 30, 36, and 43 hours, respectively. Treatment was tolerated well. There were no toxic or infectious deaths.

CONCLUSIONS

Ceftazidime's time-dependent pharmacokinetics shows the advantage of continuous infusion. This study confirmed the feasibility and safety of this administration schedule in the empiric treatment of febrile neutropenic children with cancer.

Continuous infusion versus intermittent administration of cefepime in patients with Gram-negative bacilli bacteraemia

The objective of this study was to compare the pharmacokinetics of cefepime administered by continuous infusion and intermittent injection regimens. A prospective, randomized, cross-over study of ten patients with Gram-negative bacilli bacteraemia was conducted. All patients were randomized to receive cefepime either as a 4-g continuous infusion over 24 h for 48 h or a 2-g bolus administered intermittently intravenously every 12 h for 48 h. After 48 h the patients received the alternative dose regimen. Cefepime pharmacokinetic studies were carried out during hours 36-48 after the start of both regimens. All of the pathogens isolated from the blood in 7 patients had a minimum inhibitory concentration (MIC) < 1 microg mL(-1). In both regimens, the serum cefepime concentrations at all time points were higher than the MIC for the pathogens isolated from this study. For the continuous infusion arm, the highest steady-state concentration was 49.80+/-18.40 microg mL(-1) and the lowest steady-state concentration was 41.42+/-16.48 microg mL(-1). The steady-state concentrations were greater than 4 times the MIC of 8 microg mL(-1). For the intermittent injection regimen, the mean trough concentration was 4.74+/-3.99 microg mL(-1). The mean serum cefepime concentration was above 8 microg mL(-1) for 81.66% of the dosing interval. Therefore, we conclude that either continuous infusion or intermittent injection can be used as an effective mode of cefepime administration to achieve bactericidal activity.

Penetration of cefuroxime into chronically inflamed sinus mucosa

OBJECTIVES

Despite its seeming relevance, limited information exists about antibiotic sinus tissue penetration and how it is affected by inflammation. Thus the reason for the present investigation.

STUDY DESIGN

A randomized, open, multiple-dose, pharmacological study, employing cefuroxime axetil, an approved oral antimicrobial for the treatment of acute bacterial rhinosinusitis, was developed.

METHODS

Twenty subjects, selected for surgery because of chronic rhinosinusitis, were randomly allocated to receive either a short (3-8 d) or a long (9-14 d) preoperative treatment regime with 500 mg cefuroxime axetil BID, the last dosage being taken 3 to 4 hours before surgery. At the operation, tissue samples were collected at specific sinonasal sites for both pharmacological determination of antibiotic levels and histopathological assessment of the degree of inflammation. The blood levels of the drug were simultaneously assayed.

RESULTS

Cefuroxime kinetic behavior on chronically inflamed mucosa was shown to be, for the most part, dependent on the blood levels, regardless of the inflammatory state. Distribution was even throughout the different sinus cavities, and the tissue levels were still, 3 to 4 hours after dosing, above the reported minimum inhibitory concentration (MIC) values for some of the most prevalent sinus pathogens. The extended treatment course did not seem to add any extra histopathological or pharmacological benefit.

CONCLUSIONS

Cefuroxime penetrates adequately and uniformly into chronically inflamed sinus mucosa, apparently unaffected by the degree of inflammation, in a way not dissimilar to its pharmacokinetic behavior in the normal state. Persistent MIC levels for common pathogens still warrant antimicrobial efficacy for a significant period of time after dosing.

Antibiotic use in the critical care unit

The antimicrobial management of patients in the critical care unit is complex. Not only must the clinician be familiar with a number of clinical, microbiological, pharmacological, and epidemiological observations but also fundamental pharmacodynamic concepts. It is an understanding of these concepts that forms the basis for the design of dosing strategies that maximize clinical efficacy and minimize toxicity. Antimicrobial selection is further complicated by the plethora of new antimicrobial agents available with varying clinical utility. Nowhere is this more evident than in the quinolone class of antibiotics. To aid the clinician in differentiating between quinolones it now seems reasonable to create a classification system akin to the generation grouping applied to the cephalosporins. Our classification is based upon the pharmacodynamic principles discussed within this article.

Pharmacokinetics in vivo and pharmacodynamics ex vivo/in vitro of meropenem and cefpirome in the Yucatan micropig model: continuous infusion versus intermittent injection

OBJECTIVE: To investigate the pharmacodynamic disposition of two recently developed beta-lactam antibiotics, meropenem and cefpirome, in the Yucatan micropig model, and to compare the bactericidal activity of these drugs against bacteria in this in vitro/ex vivo micropig model after administration by both intermittent injection and continuous infusion. METHODS: Cefpirome (1 g) was given to the micropig over a 12-h period by direct intravenous injection and 6-h continuous infusion (500 mg). Meropenem (250 mg) was administered either by 30-min intravenous and 8-h continuous infusion. The two drugs were assayed by HPLC. The pharmacodynamics of these drugs were evaluated by means of (1) serum killing curve against Klebsiella pneumoniae producing extended-spectrum beta-lactamase, stably derepressed Enterobacter cloacae and methicillin-susceptible penicillinase-producing Staphylococcus aureus, and (2) calculations of index of surviving bacteria (ISB). RESULTS: The bactericidal activity of meropenem against K. pneumoniae and E. cloacae in this in vitro/ex vivo model was excellent, with a 4 log decrease at peak concentrations. Meropenem produced a mixed concentration- and time-dependent, killing effect against E. cloacae and K. pneumoniae. The ISB value ranged from 25% to 30% for E. cloacae. With concentrations above MIC for S. aureus (1 mg/L), cefpirome has a time-dependent bactericidal activity, as shown by the ISB ranging from 20% to 80% after 4 h and between 20% and 40% after an 8-h drug exposure. For both antibiotics, the higher concentrations obtained just after intermittent injection had a rapid and strong killing effect against the strains tested, but the trough levels had no bactericidal activity. The continuous infusions produce consistent concentrations of antibiotic that can be maintained above the MIC, and the bactericidal activity of which ranges from 2 to 4 log10 decrease of inoculum. CONCLUSIONS: In the present study the micropig has been shown to be an adequate model for the pharmacodynamic investigation of cefpirome and meropenem. In general, continuous infusion appears to optimize the pharmacodynamic profile of the two tested beta-lactam antibiotics. However, against Gram-negative bacilli, the administration of a loading dose prior to continuous infusion of beta-lactams would eliminate the only potential pharmacokinetic disadvantage of continuous infusion and ensure the rapid onset of antimicrobial activity.

Serum bactericidal activity of ceftazidime: continuous infusion versus intermittent injections

Since beta-lactam antibiotics have concentration-independent killing, bacterial eradication is a function of the time the serum drug concentration remains above the drug's MIC (T > MIC). We compared the serum bactericidal titers (SBTs) of ceftazidime given by continuous infusion (CI) or by intermittent bolus dosing (BD) against two clinical isolates each of Pseudomonas aeruginosa and Escherichia coli to determine if CI would allow lower daily dosing while still providing equal bactericidal activity compared with BD. This was an open-labeled, randomized, steady-state, four-way crossover study with 12 healthy volunteers. The ceftazidime regimens were 1 g every 8 h (q8h) BD, 1 g q12h BD, 3 g over 24 h CI, and 2 g over 24 h CI. The areas under the bactericidal curves were calculated by the trapezoidal rule using the reciprocal of the SBT. For all organisms the areas under the bactericidal curves for intermittent versus the CI regimens were the same for equal doses (P > 0.05). For both strains of E. coli all four regimens provided SBTs of > or = 1:2 over the dosing interval and 100% T > MIC. The 1-g q8h BD and q12h BD regimens provided T > MIC of 82 and 52%, respectively, for both P. aeruginosa isolates (MICs, 4 micrograms/ml). In comparison, the 2- and 3-g CI regimens always maintained SBTs of > or = 1:2 and T > MIC over the 24-h period as serum drug concentrations were 12.8 +/- 3.0 and 18.2 +/- 4.5 micrograms/ml, respectively. CI optimizes the pharmacodynamic and pharmacoeconomic profile of ceftazidime by providing adequate antibacterial activity over the 24-h dosing period with a reduction in the total daily dose of the antimicrobial agent.

Antibiotic kinetics and dynamics for the clinician

In recent decades considerable data have been acquired concerning the complex interactions of the organism-antimicrobial-host triad. Using the current understanding of drug disposition in the body, pharmacokinetics, and in vitro microbiologic activity, optimal dosing strategies can be derived to maximize clinical efficacy and minimize potential toxicities. This article discusses pharmacokinetics, pharmadynamics, and the application of this principle in clinical practice.