Gramicidin is an antibiotic effective against gram-positive bacteria. On account of its toxic effects it is not suitable for systemic administration. It is, however, highly useful in the treatment of a number of local infections in the form of impregnated adhesive compress dressings or other forms of local application. Gramicidin inhibits the growth of a large number of micro-organisms in culture media and it was found that its application to gunshot wounds, infected ulcers, and osteomyelitic lesions leads to a rapid disappearance of bacteria from the wound. Favorable results have also been reported in the treatment of middle ear and mastoid infections, sinusitis, infectious inflammation of the conjunctiva of the eye, and even in certain bladder infections. It must be emphasized that in all these cases the drug must be applied locally, e.g., by instillation into the eye or by direct application to mastoid cavities following operation. Gramicidin is too poisonous to be used by injection. Its principal toxicity consists of its destructive effect on the red blood cells, causing hemolysis.
Gramicidin and a related antibiotic, tryocidine, which is effective against both gram-positive and gram-negative microorganisms, occur together in tyrothricin which was isolated by R. J. Dubos in 1939 from a spore forming organism, Bacillus brevis. Pure, crystalline gramicidin is a polypeptide containing many different amino acids. It is, therefore, related to proteins. It has been stated recently that the addition of formaldehyde to gramicidin solutions renders these less poisonous to tissues and red blood corpuscles while it does not impair their antibiotic efficiency.
This antibiotic is-usually supplied in a 2 percent alcoholic solution. The addition of water to this solution causes a milk-white precipitate which may remain in suspension.
