Pharmacokinetics of erythromycin after the administration of intravenous and various oral dosage forms to dogs

The purpose of this study was to describe and compare the pharmacokinetic properties of different formulations of erythromycin in dogs. Erythromycin was administered as lactobionate (10 mg/kg, IV), estolate tablets (25 mg/kg p.o.) and ethylsuccinate tablets or suspension (20 mg/kg p.o.). After intravenous (i.v.) administration, the principal pharmacokinetic parameters were (mean ± SD): AUC_(0–∞) 4.20 ± 1.66 μg·h/mL; C_max 6.64 ± 1.38 μg/mL; V_z 4.80 ± 0.91 L/kg; Cl_t 2.64 ± 0.84 L/h·kg; t_½λ 1.35 ± 0.40 h and MRT 1.50 ± 0.47 h. After the administration of estolate tablets and ethylsuccinate suspension, the principal pharmacokinetic parameters were (mean ± SD): C_max, 0.30 ± 0.17 and 0.17 ± 0.09 μg/mL; t_max, 1.75 ± 0.76 and 0.69 ± 0.30 h; t_½λ, 2.92 ± 0.79 and 1.53 ± 1.28 h and MRT, 5.10 ± 1.12 and 2.56 ± 1.77 h, respectively. The administration of erythromycin ethylsuccinate tablets did not produce measurable serum concentrations. Only the i.v. administration rendered serum concentrations above MIC₉₀ = 0.5 μg/mL for 2 h. However, these results should be cautiously interpreted as tissue erythromycin concentrations have not been measured in this study and, it is recognized that they can reach much higher concentrations than in blood, correlating better with clinical efficacy.