The International Standard for polymyxin B.

A sample of highly purified polymyxin B sulfate, which was part of the British National Standard for polymyxin B, has been examined in four laboratories in two countries, and has been assayed against the polymyxin B standard of the Food and Drug Administration of the US Department of Health, Education and Welfare. The material examined has been established as the International Standard for Polymyxin B, and the International Unit of Polymyxin B is defined as the activity contained in 0.000127 mg of the International Standard.