Relationship between acute toxicity in mice and polymorphic forms of polyene antibiotics

Marked differences in LD50 values were found between various batches of polyene antibiotics (mepartricin and nystatin) after intraperitoneal administration in suspension to mice. Such differences do not seem attributable to the particle size but to different molecular spatial arrangements of the products, which modify their solubility and biological availability. In the samples obtained by chemical treatments of some batches of the polyene substances, it has been possible to change the toxicity drastically and then to bring it back to its original value.