title: Factors affecting precipitation of vancomycin and ceftazidime on intravitreal injection.
abstract: OBJECTIVE
  The aim of this study was to investigate the factors that affect the precipitation of vancomycin and ceftazidime which are currently used in intravitreal injections for infectious endophthalmitis.
  
  
  METHODS
  The minimum concentration required for precipitation of the 2 antibiotics was estimated by 2-fold dilution. In addition, the amount of the precipitate that formed was measured at 4, 3, 2, and 1 mL volumes, temperatures (37°C or 4°C), and in different medias (balanced salt solution plus and normal saline).
  
  
  RESULTS
  When 2-fold serial dilutions of vancomycin and ceftazidime were mixed, precipitates started forming at a concentration of 12.5 mg/mL for ceftazidime and 10 mg/mL for vancomycin. The precipitation of vancomycin and ceftazidime increased at lower temperatures (4°C) and lower media volumes (1 mL). However, using a micropipette with a complete mixed media and an antibiotic (vancomycin or ceftazidime) prevented the formation of a precipitate when the other antibiotic was added.
  
  
  CONCLUSIONS
  The formation of a precipitate associated with intravitreal injections was correlated with the diffusion rate of the antibiotics in the media. Precipitation increased at lower temperatures, lower media volumes, and at higher antibiotic concentrations.
authors.affiliation: Department of Microbiology, College of Medicine, Kosin University , Pusan, Korea.
authors.forename: Indal
authors.initials: I
authors.lastname: Park
authors.forename: Sang Joon
authors.initials: SJ
authors.lastname: Lee
mesh_terms: D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000737:chemistry*; D002442:Ceftazidime / Q000008:administration & dosage / Q000737:chemistry*; D011232:Chemical Precipitation; D004058:Diffusion; D009877:Endophthalmitis / Q000188:drug therapy; D006801:Humans; D058449:Intravitreal Injections; D013696:Temperature; D014640:Vancomycin / Q000008:administration & dosage / Q000737:chemistry*
chemical_list: D000900:Anti-Bacterial Agents; D014640:Vancomycin; D002442:Ceftazidime