Pharmacodynamics of vancomycin and other antimicrobials in patients with Staphylococcus aureus lower respiratory tract infections

Vancomycin in vitro bactericidal activity and its relationship to efficacy in clearance of methicillin-resistant Staphylococcus aureus bacteremia

We examined the relationship between the time to clearance of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia while patients were receiving vancomycin therapy and the in vitro bactericidal activity of vancomycin. Vancomycin killing assays were performed with 34 MRSA bloodstream isolates (17 accessory gene regulator group II [agr-II] and 17 non-agr-II isolates) from 34 different patients with MRSA bacteremia for whom clinical and microbiological outcomes data were available. Vancomycin doses were prospectively adjusted to achieve peak plasma concentrations of 28 to 32 mug/ml and trough concentrations of 8 to 12 microg/ml. Bactericidal assays were performed over 24 h with approximately 10(7) to 10(8) CFU/ml in broth containing 16 microg/ml vancomycin. The median time to clearance of bacteremia was 6.5 days for patients with MRSA isolates demonstrating > or =2.5 reductions in log(10) CFU/ml at 24 h and >10.5 days for patients with MRSA isolates demonstrating <2.5 log(10) CFU/ml by 24 h (P = 0.025). The median time to clearance was significantly longer with MRSA isolates with vancomycin MICs of 2.0 microg/ml compared to that with MRSA isolates with MICs of < or =1.0 microg/ml (P = 0.019). The bacteremia caused by MRSA isolates with absent or severely reduced delta-hemolysin expression was of a longer duration of bacteremia (10 days and 6.5 days, respectively; P = 0.27) and had a decreased probability of eradication (44% and 78%, respectively; P = 0.086). We conclude that strain-specific microbiological features of MRSA, such as increased vancomycin MICs and decreased killing by vancomycin, appear to be predictive of prolonged MRSA bacteremia while patients are receiving vancomycin therapy. Prolonged bacteremia and decreased delta-hemolysin expression may also be related. Evaluation of these properties may be useful in the consideration of antimicrobial therapies that can be used as alternatives to vancomycin for the treatment of MRSA bacteremia.

Emerging Options for Treatment of Invasive, Multidrug-ResistantStaphylococcus aureusInfections

Limited established treatment options exist for the treatment of serious, invasive infections caused by multidrug-resistant Staphylococcus aureus, most notably nosocomially acquired methicillin-resistant S. aureus (MRSA). Although vancomycin represents the gold standard for therapy of such invasive infections, reports of increasing in vitro resistance to vancomycin, combined with reports of clinical failures (with this and other antistaphylococcal agents), underscore the need for alternative therapies. Older agents with favorable in vitro activity available in both oral and intravenous dose forms include trimethoprim-sulfamethoxazole and clindamycin. Limited clinical data exist to support their routine use as initial therapy in the treatment of invasive disease. However, these and other options (e.g., tetracyclines) are being reexplored in the setting of increasing concern over MRSA acquired in the community setting. Newer treatment options for MRSA include linezolid, quinupristin-dalfopristin, daptomycin, and tigecycline. With the exception of linezolid, these newer agents require intravenous administration. Combination therapy may be considered in select invasive diseases refractory to standard monotherapies. These diseases include infections such as endocarditis, meningitis, and prosthetic device infections. Additional alternatives to vancomycin are under clinical investigation. Those in later stages of development include oritavancin, dalbavancin, telavancin, and ceftobiprole.

Pharmacokinetic/pharmacodynamic analysis of vancomycin in ICU patients

AIMS

To identify the variables affecting vancomycin pharmacokinetics in medical ICU patients and to evaluate the potential efficacy of dosage schedules by PK/PD analysis.

DESIGN

A retrospective pharmacokinetic analysis of serum levels obtained in routine vancomycin monitoring was performed.

SETTING

A 12-bed general ICU of a university teaching hospital.

PATIENTS

Forty-six vancomycin-treated ICU patients fitting the following criteria: over 18 years old; more than three concentration data per patient; absence of renal replacement support, cardiac surgery and neoplastic disorders.

INTERVENTIONS

Clinical information was collected from the patients' medical records. Details of vancomycin therapy, dosage and blood sampling times were obtained from pharmacokinetic reports. Population analysis were made by the standard two-stage approach.

MEASUREMENTS AND MAIN RESULTS

Vancomycin clearance and distribution volume were estimated individually assuming a one-compartment pharmacokinetic model. PK/PD analysis was performed by Monte Carlo simulation. In the ICU patients, higher Vd (nearly twice the quoted value of 0.72 l/kg) and different vancomycin clearance-creatinine clearance relationship were found. Renal function, the APACHE score, age and serum albumin accounted for more than 65% of drug clearance variability. Vancomycin standard dosages led to a 33% risk of not achieving the recommended AUC(24h)/MIC breakpoint for Staphylococcus aureus.

CONCLUSIONS

The population kinetics and PK/PD analyses based on Monte Carlo simulation procedures offer an excellent tool for selecting the therapeutic option with the highest probability of clinical success in ICU patients.

Predictors of mortality for methicillin-resistant Staphylococcus aureus health-care-associated pneumonia: specific evaluation of vancomycin pharmacokinetic indices

OBJECTIVE

The goal of this investigation was to determine whether vancomycin pharmacokinetic indexes (eg, serum trough concentrations or area under the concentration curve [AUC] values) were associated with mortality for patients with health-care-associated pneumonia (HCAP) attributed to methicillin-resistant Staphylococcus aureus (MRSA).

DESIGN

A retrospective, single-center, observational cohort study.

SETTING

Barnes-Jewish Hospital, a 1,200-bed urban teaching facility.

PATIENTS

Adult patients requiring hospitalization who were identified as having HCAP attributed to MRSA by BAL semi-quantitative cultures.

INTERVENTIONS

Retrospective data collection from automated hospital, microbiology, and pharmacy databases.

MEASUREMENTS AND MAIN RESULTS

One hundred two patients with MRSA HCAP were identified over a 6.5-year period. Thirty-two patients (31.4%) died during their hospitalization. The mean (+/- SD) vancomycin trough concentrations (13.6 +/- 5.9 vs 13.9 +/- 6.7 microg/mL, respectively; p = 0.866) and AUC values (351 +/- 143 vs 354 +/- 109 microg/h/mL, respectively; p = 0.941) did not differ between survivors and nonsurvivors. The stratification of the vancomycin trough concentrations and AUC values yielded no relationship with hospital mortality.

CONCLUSIONS

We found no evidence that greater vancomycin trough concentrations or AUC values correlated with hospital outcome. Based on these results, aggressive dosing strategies for vancomycin (eg, trough concentrations of > 15 microg/mL) may not offer any advantage over traditional dose targets (range, 5 to 15 microg/mL).

Hospital-acquired pneumonia in the 21st century: a review of existing treatment options and their impact on patient care

Hospital-acquired pneumonia is a common nosocomial infection, with significant morbidity and mortality, and represents a major therapeutic challenge to clinicians. The therapeutic approach must be patient-oriented and institution-specific. The specific risk factors of each patient, such as previous antibiotic exposure, underlying diseases, length of hospital stay and the local patterns of antimicrobial resistance, should guide physicians in their decision of the initial optimal empirical therapy. Delays in the initiation or inappropriate/inadequate initial therapy are related to increased mortality and worse outcomes. In responding patients, as soon as culture data are available, efforts should be made to change the initial broad spectrum antibiotic regimen to a more targeted one (de-escalation). The optimal duration of treatment is a matter of debate, but courses longer than 1 week are rarely justified.

Optimizing antibiotic treatment for ventilator-associated pneumonia

Ventilator-associated pneumonia (VAP) is the most common infectious complication in patients receiving mechanical ventilation and accounts for exorbitant use of resources in the intensive care unit. Antimicrobial management of VAP incorporates an initial broad-spectrum, empiric regimen to ensure appropriate coverage with deescalation of therapy after 48-72 hours based on culture results and sensitivities. When VAP clinically responds to treatment, antimicrobials should be discontinued after 7-8 days to reduce overall antibiotic consumption and the selection pressure on flora observed in the intensive care unit and thus minimize the development and spread of antimicrobial resistance.

The role of vancomycin in the treatment paradigm

Vancomycin was introduced in the United States in 1956 as a possible treatment for infections due to penicillin-resistant Staphylococcus aureus, but it was not used widely because of toxicity and the nearly simultaneous development of semisynthetic antibiotics and cephalosporins. Thus, its main indication was the treatment of serious gram-positive infections in penicillin-allergic patients. For susceptible strains of S. aureus, vancomycin was more rapidly bactericidal than penicillin, nafcillin, or cefazolin, and, in a rabbit model of S. aureus endocarditis, sterilization of vegetations was more rapid with vancomycin. In clinical practice, however, nafcillin remained the treatment of choice for staphylococcal bacteremia, largely because it had failure rates of only 4%. With the appearance of methicillin-resistant S. aureus and coagulase-negative staphylococci, vancomycin became the drug of choice for these infections. Recently, the efficacy of vancomycin has been questioned because of vancomycin's increasing minimum inhibitory concentrations among staphylococci, poor tissue penetration, and apparently slower bacterial killing than previously was recognized.

The pharmacokinetic and pharmacodynamic properties of vancomycin

Vancomycin is one of only a few antibiotics available to treat patients infected with methicillin-resistant Staphylococcus aureus and methicillin-resistant, coagulase-negative Staphylococcus species. Therefore, understanding the clinical implications of the pharmacokinetic and pharmacodynamic properties of vancomycin is a necessity for clinicians. Vancomycin is a concentration-independent antibiotic (also referred to as a "time-dependent" antibiotic), and there are factors that affect its clinical activity, including variable tissue distribution, inoculum size, and emerging resistance. This article reviews the pharmacokinetic and pharmacodynamic data related to vancomycin and discusses such clinical issues as toxicities and serum concentration monitoring.

Potential Impact of Vancomycin Pulmonary Distribution on Treatment Outcomes in Patients with Methicillin-ResistantStaphylococcus aureusPneumonia

Vancomycin as the drug of choice for treatment of methicillin-resistant Staphylococcus aureus (MRSA) pneumonia has been called into question on the basis of therapeutic failures. In patients with MRSA pneumonia, treatment failures are probably due to the complex interplay of variables affecting the host-antimicrobial-pathogen interrelationship. However, it has been suggested that decreased penetration of vancomycin into the lungs may contribute. This review explores physiochemical and physiologic variables that affect pulmonary penetration and describes methods used in quantifying pulmonary vancomycin concentrations. Most important, findings are evaluated in the clinical context of the chemotherapeutic options available for treatment of MRSA pneumonia. The possibility of increased serum vancomycin concentrations as a method to optimize current treatment outcomes is also explored.

Evaluation of Clinical Efficacy of Maeda’s Nomogram for Vancomycin Dosage Adjustment in Adult Japanese MRSA Pneumonia Patients

The clinical efficacy of Maeda's nomogram for vancomycin dosage adjustment was evaluated by comparison with a standard dosage regimen (package insert information: vancomycin dose reduced in elderly patients and patients with renal dysfunction, with Moellering's nomogram used for renal-dysfunction patients) in adult Japanese MRSA pneumonia patients. Using Maeda's nomogram, the vancomycin dose is fixed at 1,000 mg while the dosing interval is varied in accordance with individual creatinine clearance. Using a standard dosage regimen, 5 patients out of 27 (18.5%) achieved target plasma levels of vancomycin (25-40 microg/mL for peak and 5-15 microg/mL for trough) within 2-6 days. Using Maeda's nomogram, 38 patients out of 53 (71.7%) achieved target levels in that time. A higher clinical response (complete resolution of all signs and symptoms of MRSA infection) to vancomycin therapy was also obtained with Maeda's nomogram when evaluated approximately 2-weeks after discontinuation of vancomycin therapy (43.4% versus 18.5% for the standard regimen). In conclusion, the Maeda's nomogram regimen with a 1,000 mg vancomycin dose was shown to achieve target plasma levels of vancomycin at a higher rate and provide higher clinical efficacy in vancomycin therapy of MRSA pneumonia patients, as compared with the currently available standard dosage regimen.