Multicomponent antibiotic substances produced by fermentation: implications for regulatory authorities, critically ill patients and generics.

Teicoplanin and polymyxin E (colistin) are antibiotics consisting of multiple, closely related subcomponents, produced by fermentation. The principal components comprise a complex mixture of chemically related, active substances (teicoplanin A(2-1)-A(2-5) and polymyxin E(1-2), respectively), which might be required to be present in specific ratios to ensure optimal antibacterial and clinical efficacy. These subcomponents differ in their fatty acid and amino acid composition and, as such, the lipophilic and protein binding characteristics differ between components. This has therapeutic implications for critically ill patients, as the volume of distribution of the teicoplanin A2 and polymyxin E analogues at the onset of an intravenous infusion may impact on expected pharmacokinetics and influence outcome.