Pharmacokinetics of methylprednisolone, methylprednisolone sodium succinate, and methylprednisolone acetate in dogs.

The absolute bioavailability and pharmacokinetic parameters of two methylprednisolone formulations (methylprednisolone sodium succinate and methylprednisolone acetate) were determined in five dogs. Plasma concentrations of methylprednisolone, methylprednisolone sodium succinate, and methylprednisolone acetate were measured by sensitive and specific high-performance liquid chromatographic methods. After intravenous methylprednisolone sodium succinate administration, methylprednisolone was released rapidly but the extent of availability was rather low (43.6%). This has been tentatively explained in terms of its subsequent single-pass metabolism in the liver, i.e., hepatic hydrolysis of methylprednisolone sodium succinate followed by immediate hepatic elimination of the released methylprednisolone. After intramuscular administration of methylprednisolone acetate, its absorption was slow (half-time of absorption, 69.04 h) and the availability of the released methylprednisolone was low (42.7%). Therapeutic implications of these results are discussed, especially those which are relevant to shock therapy.