Roxithromycin was one of the new generation erythromycins introduced in the 1980s. Improved acid stability was achieved by converting the 9-keto group to the more stable oxime and alkylation of the oxime to provide the methoxyethoxymethyl ether oxime. In vivo, roxithromycin exhibits higher tissue levels and a longer half-life while being slightly less potent than erythromycin in vitro.