Absorption of various erythromycin esters and salts in mice after intragastric intubation

Erythromycin base and its different salts and esters were given intragastrically to mice. Serum concentrations of erythromycin and its 2'-esters were determined by the bacterial growth inhibition method. Acetyl and propionyl erythromycin were the best absorbed 2'-esters, and differed significantly from butyryl erythromycin and erythromycin base. Erythromycin estolate yielded a larger area under the concentration curve than acistrate or stearate. Among the syrup preparations, erythromycin acistrate was significantly better absorbed than 2'-ethylsuccinyl erythromycin. Absorption of 2'-esters decreased with increasing number of esterified carbon atoms and increasing hydrophobicity and increasing log P value (the logarithm of octanol-water partition coefficient). In addition to sufficient lipophilicity, the optimum absorption of erythromycin esters seems to require a high hydrophilicity.