Enhancing Effect of Alkalinization of the Medium on the Activity of Erythromycin Against Gram-negative Bacteria

Abstract

The antibacterial activity of erythromycin was markedly enhanced by alkalinization of the culture medium or urine within the clinical range ( p H 6.0 to 8.2). This effect was demonstrated against recent isolates of Escherichia coli, Klebsiella pneumoniae, Enterobacter sp., and Pseudomonas aeruginosa , as well as against Staphylococcus aureus and Streptococcus faecalis . The urine of normal volunteers was made alkaline by ingestion of sodium bicarbonate or acetazolamide (Diamox) during administration of 1.0 g of erythromycin every 8 hr; such urine was capable of inhibiting E. coli and K. pneumoniae even when diluted up to (in one instance) 128 times with broth of the same p H as the urine. Undiluted urine of the same subjects, without alkalinization, was seldom capable of inhibiting these organisms. The range of p H (6.6 to 8.6) over which the antibacterial effect was enhanced coincided with that over which there was decreasing ionization of a basic group.