New ether oxime derivatives of erythromycin A. A structure-activity relationship study.

The discovery of roxithromycin is the result of a rational and scientific process, based on the fact that at least one reason for erythromycin A's resorption variability after oral administration was its instability in the gastric juice. This instability is due to the reactivity of the ketone in position 9 in acidic medium and one chemical approach was to mask it by an oxime function. Both stereoisomers of this oxime were isolated. Direct O-alkylation of this oxime allowed access to various ether oxime derivatives and of the latter the E stereoisomers were more interesting than the Z ones. The choice of the nature of the oxime substitution was made according to the lipophilic or hydrophilic character of the aliphatic ether chain and these alterations were mainly carried out by introducing heteroatoms into this chain. These different derivatives were classified in 5 groups according to the chemical nature of the chain: Aliphatic, aromatic and nitrogen-, oxygen- and sulfur-containing chains. Two classes, those containing a nitrogen or an oxygen in the ether side chains, showed differential in vitro/in vivo antibiotic activities, with improved bioavailability. Some preliminary pharmacokinetic data confirmed this improvement and led to the selection of five candidates, from which roxithromycin emerged as the best compound.

Antibacterial activity of roxithromycin: a laboratory evaluation.

Roxithromycin, formerly known as RU 28965 (9-[O [(2-methoxyethoxy)methyl]oxime]-erythromycin), is a novel 14 atom-membered semisynthetic macrolide with an antibacterial spectrum directed towards Gram-positive cocci and bacilli, Gram-negative cocci and some Parvobacteriaceae. The in vitro antibacterial activity of roxithromycin was compared with those of erythromycin and spiramycin against 275 clinical isolates by using 2-fold broth macro-dilution tests. The antibacterial spectrum of roxithromycin and erythromycin were qualitatively comparable (including the bacteriostatic type of activity and the profile of resistance), but minimal inhibitory concentrations of erythromycin were generally one half those of roxithromycin, except for Corynebacterium sp. and Bacteroides fragilis against which the new macrolide was more active. On the other hand, roxithromycin exhibited a superior in vivo antibacterial activity in laboratory animals, being up to six times more potent than erythromycin in curing experimentally infected mice. Roxithromycin showed high blood levels and long half-lives of elimination in rodents after oral administration, and its bioavailability amounted to 72% in mice and 85% in rats, compared to less than 10% for erythromycin. Roxithromycin was widely distributed throughout the body with a high degree of penetration into all tissues, particularly in the lungs.