Interaction of sucralfate with antibiotics used for selective decontamination of the gastrointestinal tract.

The interactions of sucralfate with colistin sulfate, with tobramycin sulfate, and with amphotericin B were studied. Sucralfate 500 mg was added to 40 mL of distilled water adjusted to pH 3.5 with hydrochloric acid. Stock solution of one of the three antibiotics was added to give a final colistin concentration of 50 mg/L (as the sulfate salt), final tobramycin concentration of 50 mg/L (as the sulfate salt), and final amphotericin B concentration of 25 mg/L. Samples were removed from each sucralfate-antibiotic mixture at 0, 5, 10, 15, 30, 45, 60, and 90 minutes and analyzed for antibiotic concentration by high-performance liquid chromatography (colistin), enzyme immunoassay (tobramycin), and spectrophotometry (amphotericin B). To determine if any interaction was reversible, the mixtures were stored for 90 minutes without sampling, the pH was adjusted to 6.5-7.0, and samples were removed and analyzed. All tests were performed in triplicate, and the temperature was maintained at 25 degrees C. Significant drug loss was observed starting at five minutes for each antibiotic-sucralfate mixture. This effect was not reversible in the less acidic environment. The concentrations of colistin, tobramycin, and amphotericin B declined rapidly when each drug was combined separately with sucralfate.

Selective decontamination of the digestive tract (SDD) does not prevent the formation of microbial biofilms on endotracheal tubes.

The purpose of selective decontamination of the digestive tract (SDD) is to eradicate potentially disease-producing micro-organisms from the oropharynx and gastro-intestinal tract of intensive care unit (ICU) patients, thereby reducing the incidence of nosocomial sepsis, particularly pneumonia. Microbial biofilms form on endotracheal (ET) tubes even when SDD is being administered and may represent a persistent focus for infection. The aim of this investigation was to determine the susceptibilities of organisms adherent to ET tubes to SDD antibiotics (amphotericin B, tobramycin and polymyxin) and to measure the concentrations of these agents in the tracheal aspirates of 11 patients who were being mechanically ventilated. Following extubation, a section was cut from the tip of each ET tube and any adherent microorganisms subsequently isolated were identified and their MICs determined. Samples of tracheal aspirate were obtained three hours after administration of the SDD regimen and the concentrations of the constituent antimicrobials were measured. Enterobacteriaceae were not recovered from any of the tubes but six strains of Staphylococcus aureus, three Pseudomonas spp., three enterococci and four yeasts were isolated. Wide variations in the concentrations of all antibiotics were observed and in many cases they were below the MICs for the organisms isolated. In particular, tobramycin concentrations were uniformly less than the median MIC for the S. aureus isolates and this may account for the predominance of Gram-positive bacteria adherent to the ET tubes. Microbial biofilms attached to these tubes may have a role in the pathogenesis of nosocomial pneumonia in ICU patients.

Stability of ciprofloxacin in peritoneal dialysis solution.

The long-term stability of ciprofloxacin in dialysis fluid was studied. Ciprofloxacin was added to nine 2-L bags of dialysis solution containing 1.3% dextrose to yield a nominal concentration of 25 mg/L. Three bags each were stored at 4, 20, and 37 degrees C; three 20-mL samples were removed from each bag after 0, 0.5, 1, 2, 5, 7, 10, 14, 21, 28, and 42 days and analyzed in triplicate by high-performance liquid chromatography. Additional samples were removed from each bag on day 42 and analyzed by microbiological assay with Pseudomonas aeruginosa (nine samples tested for each storage temperature studied). The net percentage of change in ciprofloxacin concentration was 0.76% after storage at 4 degrees C, 1.02% after storage at 20 degrees C, and 0.75% after storage at 37 degrees C. Antimicrobial activity after storage at all three temperatures was confirmed by microbiological assay. Ciprofloxacin 25 mg/L was stable for 42 days when stored in dialysis fluid containing 1.36% dextrose at 4, 20, and 37 degrees C.