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Office of Animal Welfare

Use of Prophylactic Antibiotics Post Irradiation in Mice

Use of Prophylactic Antibiotics Post Irradiation in Mice

Approved March 22, 2001    (Download) 

Background: Although it is recognized that several variables can effect the survival of mice following irradiation, e.g. the dose of bone marrow cells, the dose of irradiation, and the immune status of the animals, the guidelines which follow are based on the premise that 1) it is preferable to avoid the use of antibiotics all together and 2) the use of antibiotics in pseudomonas-free colonies is problematic. Our vendors report that the mice being supplied are free of pseudomonas and the RO water in the K-wing and Harborview used for the automatic watering systems and acidified water in bottles used in SPF facilities should prevent mice from acquiring the infection.

Investigators housing immunocompetent mice in SPF areas are encouraged to try an experiment without antibiotics to determine whether irradiated animals are able to survive two weeks or longer prior to hematopoietic failure. Animals found moribund before two weeks should have a sterile culture of heart blood to determine the presence or absence of pseudomonas or other opportunistic organisms and antibiotic sensitivities determined. If early mortality is observed, infectious death may be indicated and antibiotics should help the survival.

Policy: When antibiotics are used in the drinking water, one of the three protocols below are to be followed unless scientifically justified in writing and approved by the IACUC. When indicated, antibiotics should be administered as prescribed by veterinary services and approved by the IACUC. Antibiotics should be started one day prior to irradiation; after bone marrow repopulation, usually 10-14 days post irradiation, there should be no need to continue the antibiotics.

Protocol 1: Neomycin,orally by the drinking water (2mg/ml) as a single agent

Protocol 2: Gentamycin (0.8 mg) and Streptomycin (4mg) per 25 Gm mouse, S.C.,/daily
including weekends. Reduce dose by 20% for small mice (18-20 Gm)

Protocol 3: Genetically immunodeficient animals may need more “help”, for example ciprofloxacin or trimethoprim sulfamethoxizole; however, these agents pose a larger risk for interfering with experiments, which is of less concern with non-absorbable antibiotics like neomycin.

1 Although Neomycin and Polymyxin are not, a priori, excluded, the reference in Protocols in Immunology (4.6.1) recommends only Neomycin and at a dosage of 2 mg/ml. (2 Gm/L) If Neomycin is used either alone, or in combination with Polymyxin (1mg/ml or 1Gm/L), the recommended dosage should be used.