John S. Esterly

Impact of Carbapenem Resistance and Receipt of Active Antimicrobial Therapy on Clinical Outcomes of Acinetobacter baumannii Bloodstream Infections

ABSTRACT Nosocomial Acinetobacter baumannii bloodstream infections occur with significant prevalence and mortality. The relationship between carbapenem resistance in A. baumannii and patient outcomes remains unclear. A retrospective cohort study was conducted on patients with A. baumannii bacteremia. Outcomes, controlling for confounders, were compared for carbapenem-nonresistant A. baumannii (CNRAB) and carbapenem-resistant A. baumannii (CRAB). The primary outcome studied was all-cause hospital mortality, and the secondary endpoints evaluated were time to mortality, time to negative cultures, and length of stay postinfection for survivors. A total of 79 patients, 37 infected with CRAB and 42 with CNRAB, were studied. Hospital mortality was greater in the CRAB group as determined based on bivariate analysis (P < 0.01); however, this effect was nullified when controlling for relevant confounders with logistic regression and a Cox proportional-hazards model (P = 0.71 and 0.75, respectively). Values for time to mortality and time to negative cultures did not differ between the groups. The median number of days of stay postinfection for survivors was greater for the CRAB group than the CNRAB group (14 versus 6.5; P < 0.01). Patients who received active antimicrobial therapy were less likely to die (93.5% versus 74.2%; P = 0.02), regardless of carbapenem susceptibility classifications, and this result was robust in the multivariate model (P = 0.02). Trends existed for improved outcomes in patients receiving an active beta-lactam, and patients fared worse if they had received a polymyxin as an active agent. Patients with CRAB bloodstream infections were more chronically ill and had more comorbidities. Inactive therapy was more important than carbapenem susceptibility with respect to outcomes, was a strong predictor of death, and is potentially modifiable.

Drug-Induced QT-Interval Prolongation: Considerations for Clinicians

Drug‐induced proarrhythmia is a frequently encountered clinical problem and a leading cause for withdrawal or relabeling of prescription drugs. Suppression of the rapid component of the delayed rectifier potassium current, IKr, represents the principal pharmacodynamic mechanism leading to heterogeneous prolongation of the ventricular action potential and prolongation of the QT interval clinically. However, the risk of proarrhythmia by QT‐interval‐prolonging drugs is variable and critically dependent on several factors leading to multiple reductions in the cardiac repolarization reserve. As antiarrhythmic drugs that prolong the QT interval are usually aggressively managed with continuous electrocardiogram monitoring and screening for drug interactions when administered to patients who have a high risk of sudden cardiac death, their risk of mortality is not increased. However, noncardiovascular QT‐interval‐prolonging drugs, which often produce less QT‐interval prolongation compared with antiarrhythmic drugs, are found to be associated with increased rates of death in patients who have a markedly lower de novo risk of sudden cardiac death. Thus, it is important for clinicians, particularly pharmacists, to be cognizant of the levels of risk associated with varying degrees of QT‐interval prolongation caused by drugs so that they can develop strategies to either prevent or reduce the risk of proarrhythmias.

The Impact of Anti-infective Drug Shortages on Hospitals in the United States: Trends and Causes

Anti-infective shortages pose significant logistical and clinical challenges to hospitals and may be considered a public health emergency. Anti-infectives often represent irreplaceable life-saving treatments. Furthermore, few new agents are available to treat increasingly prevalent multidrug-resistant pathogens. Frequent anti-infective shortages have substantially altered patient care and may lead to inferior patient outcomes. Because many of the shortages stem from problems with manufacturing and distribution, federal legislation has been introduced but not yet enacted to provide oversight for the adequate supply of critical medications. At the local level, hospitals should develop strategies to anticipate the impact and extent of shortages, to identify therapeutic alternatives, and to mitigate potential adverse outcomes. Here we describe the scope of recent anti-infective shortages in the United States and explore the reasons for inadequate drug supply.

Prospective approach to managing antimicrobial drug shortages.

Antimicrobial drug shortages continue to increase, with few new therapeutic options available. Nationally, proposals have been offered to alleviate drug shortages; however, these recommendations are unlikely to effect change in the near future. Thus, antimicrobial stewardship leaders in acute care hospitals must develop a prospective management strategy to lessen the impact of these shortages on patient care. Herein, we describe several resources available to aid professionals in antimicrobial stewardship and healthcare epidemiology to manage drug shortages. An effective approach should include prospectively tracking shortages and maximizing inventory by appropriately managing usage. Several tenets should underpin this management. Alternative agents should be rationally chosen before the inventory of the primary agent has reached zero, ethical considerations should be taken into account, and timely notification and communication with key stakeholders should occur throughout the prescribing and dispensing process.

Evaluation of a Potential Clinical Interaction between Ceftriaxone and Calcium

ABSTRACT In April 2009, the FDA retracted a warning asserting that ceftriaxone and intravenous calcium products should not be coadministered to any patient to prevent precipitation events leading to end-organ damage. Following that announcement, we sought to evaluate if the retraction was justified. A search of the FDA Adverse Event Reporting System was conducted to identify any ceftriaxone-calcium interactions that resulted in serious adverse drug events. Ceftazidime-calcium was used as a comparator agent. One hundred four events with ceftriaxone-calcium and 99 events with ceftazidime-calcium were identified. Adverse drug events were recorded according to the listed description of drug involvement (primary or secondary suspect) and were interpreted as probable, possible, unlikely, or unrelated. For ceftriaxone-calcium-related adverse events, 7.7% and 20.2% of the events were classified as probable and possible for embolism, respectively. Ceftazidime-calcium resulted in fewer probable embolic events (4%) but more possible embolic events (30.3%). Among cases that considered ceftriaxone or ceftazidime and calcium as the primary or secondary drug, one case was classified as a probable embolic event. That patient received ceftriaxone-calcium and died, although an attribution of causality was not possible. Our analysis suggests a lack of support for the occurrence of ceftriaxone-calcium precipitation events in adults. The results of the current analysis reinforce the revised FDA recommendations suggesting that patients >28 days old may receive ceftriaxone and calcium sequentially and provide a transparent and reproducible methodology for such evaluations.

Evaluation of hepatotoxicity with off-label oral-treatment doses of voriconazole for invasive fungal infections

ABSTRACT The approved treatment dose of intravenous voriconazole is a weight-based dose of 4 mg/kg of body weight twice daily; the approved oral dosing is fixed at 200 mg twice daily. In our institution, patients frequently receive oral high-dose voriconazole at 4 mg/kg twice daily. It is unknown if higher doses are associated with increased hepatotoxicity. A retrospective cohort study of patients treated with oral voriconazole for presumed invasive fungal infection for ≥7 days was completed. Patients receiving a fixed dose (i.e., labeled dose) were frequency matched and compared to those receiving a weight-based dose (i.e., high dose). The primary endpoint of hepatotoxicity was evaluated by using NCI Common Terminology Criteria (CTC) and components of liver enzymes measuring >3× the upper limit of normal (ULN) and >5× baseline measurements. Secondary endpoints included an incidence of other adverse drug events. Twenty-five labeled-dose and 84 high-dose voriconazole patients were studied. Liver enzyme abnormalities were similar between groups, with the exception of labeled-dose patients experiencing more alkaline phosphatase (ALP) CTC >2× the baseline (P = 0.02) and ALP levels >3× the ULN (P = 0.02). Treatment with high dose was associated with the discontinuation of voriconazole for practitioner attribution of adverse drug events (P = 0.03), although reasons varied and no commonality of biomarker abnormality was identified. Multivariate analysis revealed that the duration of therapy and higher mg/kg total daily doses as interval variables were predictive of some hepatotoxicity outcomes. No difference existed in liver abnormalities for high-dose voriconazole; however, higher mg/kg doses and a longer duration of therapy may be associated with hepatotoxicity.

Genetic Mechanisms of Antimicrobial Resistance of Acinetobacter baumannii

OBJECTIVE: To summarize published data identifying known genetic mechanisms of antibiotic resistance in Acinetobacter baumannii and the correlating phenotypic expression of antibiotic resistance. DATA SOURCES: MEDLINE databases (1966-July 15, 2010) were searched to identify original reports of genetic mechanisms of antibiotic resistance in A. baumannii. DATA SYNTHESIS: Numerous genetic mechanisms of resistance to multiple classes of antibiotics are known to exist in A. baumannii, a gram-negative bacterium increasingly implicated in nosocomial infections. Mechanisms may be constitutive or acquired via plasmids, integrons, and transposons. Methods of resistance include enzymatic modification of antibiotic molecules, modification of antibiotic target sites, expression of efflux pumps, and downregulation of cell membrane porin channel expression. Resistance to β-lactams appears to be primarily caused by β-lactamase production, including extended spectrum β-lactamases (blaTEM, blaSHV, blaCTX-M. blaKPC), metallo-β-lactamases (blaIMP, blaVIM, blaSIM), and most commonly, oxacillinases (blaOXA). Antibiotic target site alterations confer resistance to fluoroquinolones (gyrA, parC) and aminoglycosides (arm, rmt), and to a much lesser extent, β-lactams. Efflux pumps (tet, ade, abe) contribute to resistance against β-lactams, tetracyclines, fluoroquinolones, and aminoglycosides. Finally, porin channel deletion (carO, oprD) appears to contribute to β-lactam resistance and may contribute to rarely seen polymyxin resistance. Of note, efflux pumps and porin deletions as solitary mechanisms may not render clinical resistance to A. baumannii. CONCLUSIONS: A. baumannii possesses copious genetic resistance mechanisms. Knowledge of local genotypes and expressed phenotypes for A. baumannii may aid clinicians more than phenotypic susceptibilities reported in large epidemiologic studies.

Predictability of Doripenem Susceptibility in Acinetobacter baumannii Isolates Based on Other Carbapenem Susceptibilities and blaOXA Gene Status

Study Objective. To better define the utility of surrogate markers for doripenem susceptibility relative to gold standard microbiology tests.

Tree-Based Models for Predicting Mortality in Gram-Negative Bacteremia: Avoid Putting the CART before the Horse.

ABSTRACT Increasingly, infectious disease studies employ tree-based approaches, e.g., classification and regression tree modeling, to identify clinical thresholds. We present tree-based-model-derived thresholds along with their measures of uncertainty. We explored individual and pooled clinical cohorts of bacteremic patients to identify modified acute physiology and chronic health evaluation (II) (m-APACHE-II) score mortality thresholds using a tree-based approach. Predictive performance measures for each candidate threshold were calculated. Candidate thresholds were examined according to binary logistic regression probabilities of the primary outcome, correct classification predictive matrices, and receiver operating characteristic curves. Three individual cohorts comprising a total of 235 patients were studied. Within the pooled cohort, the mean (± standard deviation) m-APACHE-II score was 13.6 ± 5.3, with an in-hospital mortality of 16.6%. The probability of death was greater at higher m-APACHE II scores in only one of three cohorts (odds ratio for cohort 1 [OR1] = 1.15, 95% confidence interval [CI] = 0.99 to 1.34; OR2 = 1.04, 95% CI = 0.94 to 1.16; OR3 = 1.18, 95% CI = 1.02 to 1.38) and was greater at higher scores within the pooled cohort (OR4 = 1.11, 95% CI = 1.04 to 1.19). In contrast, tree-based models overcame power constraints and identified m-APACHE-II thresholds for mortality in two of three cohorts (P = 0.02, 0.1, and 0.008) and the pooled cohort (P = 0.001). Predictive performance at each threshold was highly variable among cohorts. The selection of any one predictive threshold value resulted in fixed sensitivity and specificity. Tree-based models increased power and identified threshold values from continuous predictor variables; however, sample size and data distributions influenced the identified thresholds. The provision of predictive matrices or graphical displays of predicted probabilities within infectious disease studies can improve the interpretation of tree-based model-derived thresholds.

An analysis of the accuracy of physician-entered indications on computerized antimicrobial orders.

Affiliations: 1. Auckland District Health Board, Auckland, New Zealand; 2. Institute of Environmental Science and Research, Upper Hutt, New Zealand; 3. University of Otago, Wellington, New Zealand. Address correspondence to Dr. Deborah Anne Williamson, MD, Department of Clinical Microbiology, Auckland District Health Board, Park Road, Grafton, Auckland, New Zealand (dwilliamson@adhb.govt.nz). Infect Control Hosp Epidemiol 2012;33(10):1064-1066