title: Physicochemical properties and antibacterial activity of the precipitate of vancomycin and ceftazidime: implications in the management of endophthalmitis.
abstract: OBJECTIVE
  To study the physicochemical properties, bioavailability, and microbicidal activity of vancomycin and ceftazidime in the precipitate formed by the drugs in mixture.
  
  
  METHODS
  The precipitation of the drugs prepared in buffers in the pH range of 5.8 to 8.9, in normal saline, in balanced salt solution (BSS), and in Ringer lactate, was studied by light scatter analysis. Bioavailability and antibacterial activity of the precipitate and the supernatant were estimated using high-performance liquid chromatography (HPLC) and microbiologic assay respectively.
  
  
  RESULTS
  The scatter analysis showed precipitation of vancomycin alone at pH 7.5 and in BSS. When mixed together precipitation was observed in the mixture of the two drugs within the pH range of 6.8 to 8.0 and in all solutions. HPLC of both supernatant and precipitate showed the presence of active drugs and the microbiologic assay confirmed its inhibitory activity against bacteria. The precipitate had greater activity against Gram-positive bacteria while the supernatant showed greater activity against Gram-negative bacteria.
  
  
  CONCLUSIONS
  Vancomycin's pH dependent precipitation occurs regardless of the presence of ceftazidime. The precipitate as well as the supernatant retains significant antibacterial activity thus confirming the efficacy of combination therapy with vancomycin and ceftazidime in the management of bacterial endophthalmitis.
authors.affiliation: Kanuri Santhamma Vitreo-Retina Services, Hyderabad Eye Research, LV Prasad Eye Institute, Hyderabad, India.
authors.forename: Biju
authors.initials: B
authors.lastname: Raju
authors.forename: Tinku
authors.initials: T
authors.lastname: Bali
authors.forename: Geetha
authors.initials: G
authors.lastname: Thiagarajan
authors.forename: Venkateshwara
authors.initials: V
authors.lastname: Rao
authors.forename: Taraprasad
authors.initials: T
authors.lastname: Das
authors.forename: Savitri
authors.initials: S
authors.lastname: Sharma
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000493:pharmacokinetics / Q000494:pharmacology*; D001682:Biological Availability; D002442:Ceftazidime / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology; D011232:Chemical Precipitation; D002851:Chromatography, High Pressure Liquid; D004338:Drug Combinations; D009877:Endophthalmitis / Q000188:drug therapy* / Q000378:metabolism; D004926:Escherichia coli / Q000187:drug effects*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008826:Microbial Sensitivity Tests; D013050:Spectrometry, Fluorescence; D013211:Staphylococcus aureus / Q000187:drug effects*; D014640:Vancomycin / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D004338:Drug Combinations; D014640:Vancomycin; D002442:Ceftazidime