title: An in vitro study on the compatibility and precipitation of a combination of ciprofloxacin and vancomycin in human vitreous.
abstract: OBJECTIVE
  To investigate the precipitation process of a mixture of vancomycin and ciprofloxacin by equilibrium dialysis and its subsequent effect on the level of available free antibiotics.
  
  
  METHODS
  Concentrations of vancomycin and ciprofloxacin in an equilibrium dialysis chamber were measured during the equilibrium process by high performance liquid chromatography and fluorescence polarisation immunoassay. Normal saline (NS), balanced salt solution plus (BSS Plus), and vitreous were used separately as the medium of dialysis.
  
  
  RESULTS
  Precipitation of ciprofloxacin occurred on incubation at 37 degrees C. It formed precipitate on its own or when mixed with vancomycin in all the three media of NS, BSS Plus, and vitreous. There was more precipitation at higher initial ciprofloxacin concentrations; at 25.0 mg/l about 75% free drug in BSS Plus was lost after 72 hours. The extent of precipitation was similar in both NS and BSS Plus. In the dialysis chambers, 20 mg/l ciprofloxacin dialysed against 125 mg/l vancomycin was reduced to a concentration about 5.0 mg/l after 168 hours. Precipitation of vancomycin was negligible. Ciprofloxacin precipitated in vitreous at body temperature, irrespective of the presence of vancomycin. Even after precipitation, the resultant concentration of ciprofloxacin was still higher than the MIC(90) of the drug against most Gram negative organisms.
  
  
  CONCLUSIONS
  Based on this in vitro study, ciprofloxacin precipitated in vitreous at body temperature, irrespective of the presence of vancomycin or the medium for intravitreal injection. The resultant amount of ciprofloxacin was still higher than the MIC(90) of the drug against most Gram negative organisms after precipitation. The authors suggest ciprofloxacin in place of ceftazidime when used in combination with vancomycin for treatment of infective endophthalmitis.
authors.affiliation: Department of Microbiology, The Chinese University of Hong Kong, Hong Kong, ROC.
authors.forename: M
authors.initials: M
authors.lastname: Hui
authors.forename: A K H
authors.initials: AK
authors.lastname: Kwok
authors.forename: C P
authors.initials: CP
authors.lastname: Pang
authors.forename: S W
authors.initials: SW
authors.lastname: Cheung
authors.forename: R C Y
authors.initials: RC
authors.lastname: Chan
authors.forename: D S C
authors.initials: DS
authors.lastname: Lam
authors.forename: A F B
authors.initials: AF
authors.lastname: Cheng
mesh_terms: D000368:Aged; D001831:Body Temperature; D011232:Chemical Precipitation; D002851:Chromatography, High Pressure Liquid; D002939:Ciprofloxacin / Q000737:chemistry* / Q000494:pharmacology; D003956:Dialysis; D004347:Drug Interactions; D004355:Drug Stability; D004359:Drug Therapy, Combination / Q000737:chemistry*; D006090:Gram-Negative Bacteria / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D012965:Sodium Chloride / Q000737:chemistry; D014640:Vancomycin / Q000737:chemistry*; D014822:Vitreous Body / Q000737:chemistry*
chemical_list: D012965:Sodium Chloride; D002939:Ciprofloxacin; D014640:Vancomycin