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Pharmacokinetics and pharmacodynamics of linezolid in obese patients with cellulitis.

AbstractBACKGROUND:
Linezolid is an oxazolidinone antimicrobial with excellent oral bioavailability and tissue penetration and is active against multidrug-resistant skin/soft tissue pathogens.
OBJECTIVE:
To study the pharmacokinetics and antibacterial activity of linezolid against selective skin/soft tissue pathogens in obese patients.
METHODS:
We obtained multiple serum samples from 7 obese patients (>50% over their calculated ideal body weight) receiving oral linezolid 600 mg every 12 hours for treatment of cellulitis. Following a minimum of 3 doses, serum concentrations of linezolid were measured in each subject prior to (trough) and 1 and 6 hours after a dose. These samples were then tested against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) (linezolid minimum inhibitory concentrations [MICs] 1.0, 2.0, 4.0 microg/mL) and one strain each of vancomycin-resistant Enterococcus faecium (VRE) (MIC 2.0 microg/mL), Bacteroides fragilis (MIC 2.0 microg/mL), and Peptostreptococcus magnus (MIC 1.0 microg/mL). Serum inhibitory titers (SITs) and bactericidal titers (SBTs) were measured at each time point, and the median activity for these 7 patients was calculated.
RESULTS:
Mean linezolid serum concentrations were 4.2, 12.3, and 7.2 microg/mL at these respective time points. Median SITs for 12 hours (100% of the dosing interval) were observed against each organism with the exception of the least susceptible strain of MRSA (MIC 4.0 microg/mL); serum inhibitory activity was observed only at the one-hour time point against this isolate. Furthermore, prolonged (> or =6 h) median SBTs were observed against one isolate of MRSA (MIC 1.0 microg/mL) as well as the strain of VRE and P. magnus.
CONCLUSIONS:
Serum concentrations of oral linezolid in this patient population were diminished compared with those of healthy volunteers, but still provided prolonged serum inhibitory activity against common pathogens associated with skin/soft tissue infections. One treatment concern would be an obese patient receiving oral linezolid who was infected with a less susceptible (MIC > or =4.0 microg/mL) strain of S. aureus. Bactericidal activity was also observed against selective pathogens.
AuthorsGary E Stein, Sharon L Schooley, Charles A Peloquin, Vivek Kak, Daniel H Havlichek, Diane M Citron, Kerin L Tyrrell, Ellie J C Goldstein
JournalThe Annals of pharmacotherapy (Ann Pharmacother) Vol. 39 Issue 3 Pg. 427-32 (Mar 2005) ISSN: 1060-0280 [Print] United States
PMID15701775 (Publication Type: Clinical Trial, Journal Article, Research Support, Non-U.S. Gov't)
Chemical References
  • Acetamides
  • Anti-Bacterial Agents
  • Oxazolidinones
  • Linezolid
Topics
  • Acetamides (pharmacokinetics, pharmacology)
  • Adult
  • Aged
  • Aged, 80 and over
  • Anti-Bacterial Agents (pharmacokinetics, pharmacology)
  • Area Under Curve
  • Cellulitis (complications, drug therapy, microbiology)
  • Drug Resistance, Multiple, Bacterial
  • Female
  • Half-Life
  • Humans
  • Linezolid
  • Male
  • Microbial Sensitivity Tests
  • Middle Aged
  • Obesity (complications)
  • Oxazolidinones (pharmacokinetics, pharmacology)
  • Serum Bactericidal Test
  • Skin Diseases, Bacterial (complications, drug therapy, microbiology)
  • Soft Tissue Infections (complications, drug therapy, microbiology)

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