RADIOACTIVITY DISTRIBUTION WAS DETERMINED IN SERUM AND MILK OF LACTATING EWES AFTER PARENTERAL ADMINISTRATION OF FIVE LABELED ANTIBIOTICS: (14)C-benzylpenicillin G, (3)H-dihydrostreptomycin, (3)H-tetracycline, (14)C-chloramphenicol, and (14)C-spiramycin. Antibiotic levels were measured simultaneously by microbiological assay. Radiochemical and microbiological assay procedures presented similar ...

A microbiological assay for the measurement of methotrexate has been designed, using a chloramphenicol resistant mutant of Lactobacillus casei as the test organism. The method is simple, precise and inexpensive. Results are not significantly different from those obtained using a methotrexate radioassay kit employing a competitive protein binding technique. However, where patients are being trea...