Comparative stability of oxytetracycline and tylosin in sugar syrup

Measurements of OTC stability in apicultural dosage forms have relied on me thods (fluorescence, bactericidal effects) that are not specific to OTC. We have measured the stability of OTC and tylosin in sucrose syrup using high -performance liquid chromatography. At 34 degrees C in the dark, OTC in syr up made from highly purified sucrose had a half life of 7.6 days. Tylosin w as considerably more stable, with a half life of 186 days: the half life of the total tylosin complex was 287 days. In syrup prepared from commercial- grade sugar both materials were less stable, with OTC having a half life of 6.3 days and tylosin about 75 days. Microbiological data paralleled these findings, with a rapid decrease of inhibition zone against Paenibacillus la rvae with OTC, and a persistence of inhibition with tylosin. (C) Inra/DIB/A GIB/Elsevier, Paris.