Erythromycin A 9-oxime is a semi-synthetic analogue of erythromycin prepared as means of overcoming acid lability and improving oral absorption of erythromycin A while retaining comparable antibacterial potency. Although not developed as a commercial product, erythromycin oxime was pivotal in the development of the ring expanded aza-erythromycins (e.g. azithromycin) and the oxime ethers (e.g. roxithromycin).