Admixture in commercial tetracycline preparations

: The content of admixtures in tetracycline stored under different conditions was determined with chromatographic and spectrophotometric methods. Biological activity, toxicity and colour of the drugs was tested. The changes in teh colour of tetracycline most pronounced on its storage at a temperature of 37 degrees C and elevated humidity were not accompanied by an increase in the content of anhydrotetracyclines. In parallel with the changes in the colour of tetracycline, the loss of its biological activity up to 30 per cent and increased toxicity were registered. The LD50 decreased by 40 per cent as compared to the initial level. Simultaneously an additional spot with high chromatographic mobility (Rf 0.98--1.0) was detected on thin-layer chromatograms. It was shown that the processes of tetracycline degradation resulting in marked darkening of the drug colour were not accompanied by an increase in the content of anhydro admixtures. They were probably the result of accumulation of other products which are as highly toxic and low active as the anhydroderivatives of tetracycline.