title: Once-daily gentamicin administration for community-associated methicillin resistant Staphylococcus aureus in an in vitro pharmacodynamic model: preliminary reports for the advantages for optimizing pharmacodynamic index.
abstract: OBJECTIVE
  Community-associated methicillin resistant Staphylococcus aureus (CAMRSA) infections are increasing. Although gentamicin (GEN) is usually susceptible against CA-MRSA, GEN is rarely considered for treatment as monotherapy. We employed an in vitro pharmacodynamic model (IVPDM) to compare efficacies of GEN against CA-MRSA with two dosing regimens [thrice-daily (TD), once-daily (OD)].
  
  
  METHODS
  Using two strains of CA-MRSA, we adopted IVPDM comprised of two-compartments with a surface-to-volume ratio of 5.34 cm(-1). GEN regimens were simulated with human pharmacokinetic data of TD and OD. Experiments were performed over 48 hours in triplicate for each strain and dosing regimen.
  
  
  RESULTS
  MICs of GEN for YSSA1 and YSSA15 were 1 and 2 mg/L, respectively. In OD, indices of peak/MIC were > 8.6 at least, in contrast to < 6.4 in TD. A > or = 3-log(10) reduction in CFU/mL was demonstrated prior to 4 hours in TD and OD, and continued until 8 hours for both strains. However, reductions in the colony counts at 24 and 48 hours were significantly larger for OD compared to TD in both strains (p < 0.001). During TD, resistance developed in YSSA1 and small colony variants (SCVs) were documented in YSSA15. No resistance or SCVs were observed during OD in both strains.
  
  
  CONCLUSIONS
  TD and OD showed the same killing slopes until 8 hours. After the 24 hours of experiments, OD of GEN would be advantageous not only in having more reductions in colony counts, but also suppressing the development of resistance or SCVs for 48 hours.
authors.affiliation: Department of Internal Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea.
authors.forename: Sun Woo
authors.initials: SW
authors.lastname: Kim
authors.forename: Dong-Gun
authors.initials: DG
authors.lastname: Lee
authors.forename: Su-Mi
authors.initials: SM
authors.lastname: Choi
authors.forename: Chulmin
authors.initials: C
authors.lastname: Park
authors.forename: Jae-Cheol
authors.initials: JC
authors.lastname: Kwon
authors.forename: Si-Hyun
authors.initials: SH
authors.lastname: Kim
authors.forename: Sun Hee
authors.initials: SH
authors.lastname: Park
authors.forename: Jung-Hyun
authors.initials: JH
authors.lastname: Choi
authors.forename: Jin-Hong
authors.initials: JH
authors.lastname: Yoo
authors.forename: Wan-Shik
authors.initials: WS
authors.lastname: Shin
mesh_terms: D000900:Anti-Bacterial Agents / Q000008:administration & dosage* / Q000493:pharmacokinetics / Q000494:pharmacology*; D004334:Drug Administration Schedule; D005839:Gentamicins / Q000008:administration & dosage* / Q000493:pharmacokinetics / Q000494:pharmacology*; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects*; D008826:Microbial Sensitivity Tests
chemical_list: D000900:Anti-Bacterial Agents; D005839:Gentamicins