Pharmacokinetics and Pharmacodynamics of Linezolid in Obese Patients with Cellulitis

Staphylococcus epidermidis is cleared from biomaterial implants but persists in peri-implant tissue in mice despite rifampicin/vancomycin treatment

Infections associated with implanted biomedical devices (BAI) are predominantly caused by Staphylococcus epidermidis. We previously observed in murine experimental BAI that S. epidermidis persists in peri-implant tissue rather than on the implanted biomaterial itself (Boelens et al., J Infect Dis 2000;181:1337-1349; Broekhuizen et al., Infect Immun 2007;75:1129-1136). To investigate the efficacy of rifampicin/vancomycin to clear S. epidermidis from implants and peri-implant tissues, mice with two implants were challenged with 10(7) cfu S. epidermidis per implant and received daily injections of rifampicin (25 mg/kg) and vancomycin (50 mg/kg). On the day of termination, implants and peri-implant tissue were collected and processed for culture and histology. After 1 and 8 days, implants of control mice were culture positive in 14/18 and 5/16 cases, respectively, and tissue biopsies were all culture positive. In the antibiotic-treated mice, bacteria were recovered from only 1/18 and 1/16 implants after 1 and 8 days, respectively, whereas the tissues were culture positive in 14/18 and 7/16 biopsies, respectively. In microscopy, bacteria were seen in the tissue at a distance of several cell layers from the tissue-implant interface, colocalized with host cells. Thus, although a regimen of rifampicin/vancomycin sterilized the implants, S. epidermidis persisted in peri-implant tissue, which might be an as yet unrecognized reservoir in the pathogenesis of BAI.

Antimicrobial dosing considerations in obese adult patients

As obesity continues to increase in prevalence throughout the world, it becomes important to explore the effects that obesity has on antimicrobial disposition. Physiologic changes in obesity can alter both the volume of distribution and clearance of many commonly used antimicrobials. These changes often present challenges such as estimation of creatinine clearance to predict drug clearance. Although these physiologic changes are increasingly being characterized, few studies assessing alterations in tissue drug distribution and the effects of obesity on antimicrobial pharmacokinetics have been published. The available data are most plentiful for antibiotics that historically have included clinical therapeutic drug monitoring. These data suggest that dosing of vancomycin and aminoglycosides be based on total body weight and adjusted body weight, respectively. Obese patients may require larger doses of beta-lactams to achieve similar concentrations as those of patients who are not obese. Fluoroquinolone pharmacokinetics are variably altered by obesity, which prevents a uniform approach. Data on the pharmacokinetics of drugs that have activity against gram-positive organisms-quinupristin-dalfopristin, linezolid, and daptomycin-reveal that they are altered in the presence of obesity, but more data are needed to solidify dosing recommendations. Limited data are available on nonantibacterials. An understanding of the physiologic changes in obesity and the available literature on specific antibiotics is valuable in providing a framework for rational selection of dosages in this increasingly common population of obese patients.

Pharmacokinetic and Pharmacodynamic Aspects of Antibiotic Use in High-Risk Populations

The study of pharmacokinetics includes the absorption, distribution, metabolism, and elimination of drugs. The pharmacologic effect that a medication has on the body is known as pharmacodynamics. With antimicrobials, pharmacokinetic and pharmacodynamic parameters become especially important because of the association between host drug concentrations, microorganism eradication, and resistance. This article focuses on the pharmacokinetic changes that can occur with antimicrobials when they are used in patients at high risk of infections and how they influence pharmacodynamic effects. The populations described here include patients with obesity and diabetes mellitus, renal or hepatic failure, chronic lung disease, severe burns, and long-term prosthetic devices and the elderly.

Obesity in critical care

PURPOSE OF REVIEW

To review literature germane to the care of critically ill obese patients with emphasis upon the pathophysiology of obesity and its impact on clinical management.

RECENT FINDINGS

Obesity continues to be a health epidemic of the industrialized world, and is associated with substantial morbidity and mortality. Chronic obesity results in derangements in cardiovascular, respiratory and metabolic function. Drug administration may be effected depending on the lipophilicity of the molecule administered. The ability to gain vascular access is often impaired because of large body habitus and should be aided with ultrasound guidance. The fidelity of blood pressure monitoring can also be adversely affected, necessitating the use of direct intraarterial monitoring.

SUMMARY

Obesity has pathophysiologic effects upon all major organ systems. A thorough knowledge of these effects and specific intensive care unit-related issues are necessary for clinicians to anticipate common complications and provide timely and effective treatment for the obese intensive care unit patient.

Obesity and infection

Obesity increases morbidity and mortality through its multiple effects on nearly every human system. However, the various aspects of the association between obesity and infection have not been reviewed. Thus, we reviewed the relevant literature focusing on clinical aspects of this association. Obesity has a clear but not yet precisely defined effect on the immune response through a variety of immune mediators, which leads to susceptibility to infections. Data on the incidence and outcome of specific infections, especially community-acquired infections, in obese people are so far limited. The available data suggest that obese people are more likely than people of normal weight to develop infections of various types including postoperative infections and other nosocomial infections, as well to develop serious complications of common infections. Large prospective studies are required to further define the burden of infectious morbidity and mortality conferred by obesity.

Critical care of the bariatric patient

OBJECTIVE

To synthesize the current literature on care of obese, critically ill, and bariatric surgical patients.

DATA SOURCE

A MEDLINE/PubMed search from 1966 to August 2005 was conducted using the search terms obesity, bariatric surgery, and critical illness, and a search of the Cochrane Library was also conducted.

DATA EXTRACTION AND SYNTHESIS

An increase in both the prevalence of obesity and the number of bariatric procedures performed has resulted in an increased number of obese and, specifically, bariatric surgical patients who require intensive care unit care. Obesity is a chronic inflammatory state with resultant effects on immune, metabolic, respiratory, cardiovascular, gastrointestinal, hematologic, and renal function. Principles of care of the critically ill obese patient are reviewed and then applied to critically ill bariatric surgical patients. Pharmacotherapy, vascular access, and the presentation and management of both pressure-induced rhabdomyolysis and anastomotic failure after bariatric surgery are also reviewed.

CONCLUSIONS

Obesity causes a range of pathologic effects on all major organ systems. Knowledge of these effects and issues specific to the intensive care unit care of bariatric patients can help to predict and manage complications in this population.

Update on linezolid: the first oxazolidinone antibiotic

Linezolid is the first of an entirely new class of antibiotics, the oxazolidinones, in decades. It has a spectrum of activity against virtually all important Gram-positive pathogens. The unique mechanism of action of linezolid makes cross-resistance with other antimicrobial agents unlikely. Linezolid has both intravenous and oral formulations and the latter is 100% bioavailable. Since its first approval and marketing in March 2000 in the US, linezolid has gained approval for use in many other countries for the treatment of community-acquired and nosocomial pneumonia, complicated and uncomplicated skin and soft-tissue infections, and infections caused by methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci, including cases with concurrent bacteraemia. Several earlier comprehensive reviews summarised the chemistry, mechanism of action, pharmacokinetics, clinical efficacy and safety profile of linezolid. The present review provides an update on the latest data regarding the antimicrobial activity of linezolid versus other commonly used agents, the clinical and health-economic outcomes of linezolid versus vancomycin and teicoplanin, and safety issues.