1. Product. Bacitracin

2. Like tyrothricin, the first useful antibiotic obtained from bacterial cultures, bacitracin is a complex mixture of polypeptides. So far, at least 10 polypeptides have been isolated by countercurrent distribution techniques: A, A1, B, C, D, E, F1, F2, F3, and G. The commercial product known as bacitracin is a mixture of principally A, with smaller amounts of B, D, E, and F1–3.

3. The official product is a white to pale buff powder that is odorless or nearly so. In the dry state, bacitracin is stable, but it rapidly deteriorates in aqueous solutions at room temperature. Because it is hygroscopic, it must be stored in tight containers, preferably under refrigeration. The stability of aqueous solutions of bacitracin is affected by pH and temperature.

4. Slightly acidic or neutral solutions are stable for as long as 1 year if kept at a temperature of 0 to 5°C. If the pH rises above 9, inactivation occurs very rapidly. For greatest stability, the pH of a bacitracin solution is best adjusted to 4 to 5 by the simple addition of acid. The salts of heavy metals precipitate bacitracin from solution, with resulting inactivation.

5. Ethylenediaminetetraacetic acid (EDTA) also inactivates bacitracin, which led to the discovery that a divalent ion (i.e.,Zn2+) is required for activity. In addition to being water soluble, bacitracin is soluble in low-molecular-weight alcohols but insoluble in many other organic solvents, including acetone, chloroform, and ether.

6. The activity of bacitracin is measured in units per milligram
The activity of bacitracin is measured in units per milligram. The potency per milligram is not less than 40 units/mg except for material prepared for parenteral use, which has a potency of not less than 50 units/mg. It is a bactericidal antibiotic that is active against a wide variety of Gram-positive organisms, very few Gram-negative organisms, and some others. It is believed to exert its bactericidal effect through inhibition of mucopeptide cell wall synthesis. Its action is enhanced by zinc.