Intravenous Pharmacokinetics and in Vitro Protein-Binding Studies of two New Salts of Erythromycin

Erythromycin pharmacokinetics were examined for two new salts of erythromycin, erythromycin melibionate and erythromycin penicillanate using erythromycin lactobionate for comparison, following intravenous injection to rabbits. The biological half-lives of erythromycin in serum were 99 minutes for erythromycin melibionate, 121 minutes for erythromycin penicillanate and 103 minutes for erythromycin lactobionate. Post intravenous administration serum erythromycin levels were adequately described by two compartment model kinetics, and values for the distribution volume of the central compartment and the overall distribution have been given. Estimated erythromycin distribution volumes may facilitate calculation of absorption efficiencies of erythromycin and its salts after oral doses. Serum protein binding study using horse serum showed that erythromycin melibionate, erythromycin penicillanate and erythromycin base were bound to the serum protein to the extent of 87.16%, 89.41% and 88.83% respectively; and released from the drug-protein complex to the extent of 11.25%, 8.66% and 10.66% respectively.