Soft drugs. 1. Labile quaternary ammonium salts as soft antimicrobials.

Strategies for the design of safer drugs are discussed. The various classes of "soft drugs" are designed to avoid undesired metabolic disposition (primarily various oxidative routes, occurring via possible toxic intermediates) and to be metabolized by a predictable manner with controlled rates. As a first example for the "soft analogue" type drugs, a new class of antimicrobial, surface-active quaternary salts of the type RCOOCHR1--N+ comes from X- was developed. These "soft" quaternary salts are isosteric analogues of known "hard" quaternary surfactants and are characterized by predictable and controllable cleavage (metabolism) to nontoxic components, while showing good activity against a wide range of bacteria. Due to their soft nature (low toxicity), the new antimicrobials are much safer than the conventional, hard analogues.