The comparative toxicity of antibiotics to skin.

The toxicity of sixteen antibiotics to skin in vitro was investigated by a microrespirometer technique and by the histological appearance of 3-day cultures. There was close agreement between the results obtained by the two methods and between tests with human and with guinea-pig skin. Antibiotic concentrations which caused more than 30% respiratory damage after one day invariably produced abnormal cultures, and more than 60% respiratory damage often resulted in necrotic cultures. Dose/response curves were obtained for the effect of antibiotics upon skin respiration. Mathematical evaluation had little advantage over visually fitted dose/response curves. The ED50 provided a reproducible measure of the relative toxicity of different antibiotics to skin, but the ED30 probably provided a better comparison because this was the highest concentration of antibiotic which permitted migration of epithelium. Many antibiotics at therapeutic concentrations show little toxic effect upon skin in vitro. It is suggested that the healing of surface lesions might well be retarded if the antibiotic concentration found toxic in vitro were maintained at a similar concentration in vivo.