Fluorometric determination of tetracyclines in small blood and tissue samples.

A reported fluorometric method to determine tetracycline in biological material was modified to determine low levels of the antibiotics when using only small amounts of starting material. The method is applicable to tissue distribution studies in small experimental animals and also can be used for serial determinations in blood samples of these animals and for biopsy material. The tetracyclines are extracted in the presence of ethylenediaminetetraacetic acid, and the phosphate precipitation steps are omitted. This omission makes the procedures considerably less time consuming. The recoveries of the tetracyclines, oxytetracycline and doxycycline, are approximately 80-100%. The values obtained by this method were consistent with those from microbiological assays, and its reliability was shown further in a comparison with the fate of radioactive tetracycline.