Tigecycline for treating bloodstream infections: a critical analysis of the available evidence

Dose optimisation based on pharmacokinetic/pharmacodynamic target of tigecycline

Tigecycline, a new first-in-class glycylcycline antibiotic, has shown promising efficacy against a broad range of micro-organisms. It is widely prescribed for various infections, with most prescriptions being considered for off-label use. However, only a few years after its approval by the US Food and Drug Administration (FDA), tigecycline is suspected of increasing all-cause mortality. Some clinicians have suggested such unfavourable outcomes correlate with inadequate drug exposure at the infection site. The pharmacokinetic/pharmacodynamic (PK/PD) profile of a drug plays an important role in predicting its antibiotic effect, which for tigecycline is determined as the ratio of area under the concentration-time curve (AUC) to minimum inhibitory concentration (MIC). In this study, PK/PD targets based on infection sites, bacterial isolates and patient populations are discussed. Generally, a higher dosage of tigecycline for the treatment of serious infections has been recommended in previous reports. However, the latest finding of tigecycline's atypical protein binding property requires consideration when recommending further use. In addition, combination therapy with other antibiotics provides another option by potentially lowering the MICs of multidrug-resistant bacteria.

The clinical impact of multidrug-resistant gram-negative bacilli in the management of septic shock

Multi-antibiotic drug-resistant (MDR) gram-negative bacilli are becoming a major threat to the standard care of septic patients. Empiric antimicrobial drug regimens to cover likely bacterial pathogens have to be altered in keeping with the spread of MDR pathogens in the health care setting and in the community. Reliable antibiotics for broad spectrum coverage for sepsis such as extended spectrum β-lactam antibiotics, carbapenems, and fluoroquinolones can no longer be counted upon to provide activity against a range of common, virulent pathogens that cause sepsis. In some regions of Asia, South America, and Eastern Europe in particular, MDR pathogens have become a major concern, necessitating the use of potentially toxic and costly antibiotic combinations as initial antibiotic therapy for septic shock. In this brief review, we will focus on the emergence of MDR gram-negative pathogens, resistance mechanisms, and suggest some management and prevention strategies against MDR pathogens.

[Tigecycline for treatment of severe infections in intensive care: a drug use evaluation]

OBJECTIVES

To report our experience of tigecycline use in a medical and surgical intensive care unit. To describe its prescription, microbiology findings, tolerance and efficacy.

STUDY DESIGN

Prospective, observational, single center study.

PATIENTS AND METHODS

All consecutive patients treated with tigecycline were included. Demography, indication of treatment, bacteriology before, during and in the month after treatment and ICU mortality were collected. The main endpoints were clinical and microbiological efficacy and tolerance.

RESULTS

Twenty-four patients were included. In half of the cases, tigecycline was prescribed in monotherapy for a complicated intra-abdominal infection. Overall tolerance of tigecycline was good. Clinical and microbiological cure was obtained in six cases, not obtained in nine, indeterminate in six cases and not evaluable in the three cases of prophylaxis. During the treatment, four bacteria commonly sensitives were shown to be resistant to tigecycline.

CONCLUSION

Our pilot study on 24 patients suggests that tigecycline is well tolerated in critically ill patients. Clinical cure in severe infections was compromised in nine patients essentially because of resistant pathogens suggesting its prescription on antibiogram. However, the impact of association or the increasing doses in severe critically ill patients should be evaluated.

ramR mutations in clinical isolates of Klebsiella pneumoniae with reduced susceptibility to tigecycline

Five Klebsiella pneumoniae isolates with reduced susceptibility to tigecycline (MIC, 2 microg/ml) were analyzed. A gene homologous to ramR of Salmonella enterica was identified in Klebsiella pneumoniae. Sequencing of ramR in the nonsusceptible Klebsiella strains revealed deletions, insertions, and point mutations. Transformation of mutants with wild-type ramR genes, but not with mutant ramR genes, restored susceptibility to tigecycline and repressed overexpression of ramA and acrB. Thus, this study reveals a molecular mechanism for tigecycline resistance in Klebsiella pneumoniae.

Gram-negative bloodstream infections

Gram-negative bloodstream infection (BSI) is both dangerous and challenging. The incidence of Gram-negative BSI rises with age in both men and women, but there are still some gender differences in terms of aetiology and acquisition. Clinical elements such as organ dysfunction are helpful in determining prognosis. During the last few years we have observed dramatic increases in resistance among Gram-negative organisms, including those causing bloodstream infections. Gram-negative pathogens producing extended-spectrum beta-lactamases are now common, and are associated with high rates of inadequate empirical treatment and mortality. In addition, carbapenem resistance is increasing, leaving clinicians with limited therapeutic options. Better knowledge of local epidemiology can help to optimize therapies. The use of cefepime has been questioned based on a recent meta-analysis showing increased mortality in patients treated with the drug. However, an analysis performed by the US Food and Drug Administration has not confirmed these results. Unfortunately, antimicrobial development has not kept pace with resistance, particularly for Gram-negative pathogens. We need therefore to better utilize current antibiotics and undertake rigorous infection control measures to prevent these life-threatening infections.