The effect of antibiotics on rats receiving a vitamin B12-deficient diet

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Abstract
1. Rats fed on a vitamin B12-deficient or -supplemented diet were given either neomycin or a mixture of streptomycin and erythromycin by mouth for between 7 and 15 d. The urinary excretion of methylmalonic acid and the levels of vitamin B12 in plasma and tissues and of acetic and propionic acids in caecal contents were measured.2. Both treatments caused prompt reduction of methylmalonate excretion in the deficient rats. This was apparently due to depression of the production of some precursor of methyl-malonic acid, probably propionate, rather than to an immediate effect on vitamin B12 nutrition.3. After withdrawal of the antibiotics, neomycin-treated vitamin B12-deficient rats appeared to become partly repleted in vitamin B12, but the change in the vitamin B12 status of those which had received streptomycin and erythromycin was much smaller.