Dexamethasone and prednisolone in the horse: pharmacokinetics and action on the adrenal gland.
Pharmacokinetics of dexamethasone and prednisolone were studied in 6 horses given dexamethasone alcohol (IV or IM) or dexamethasone 21-isonicotinate as a solution IV or IM (50 micrograms/kg of body weight), prednisolone 21-sodium succinate IV or IM (0.6 mg/kg of body weight), or prednisolone acetate IM (0.6 mg/kg of body weight). Plasma concentrations were determined using a high-performance liquid chromatographic method. After dexamethasone alcohol (IV) or dexamethasone 21-isonicotinate (IV), the half-life of elimination was similar (53 minutes) for both formulations. After dexamethasone (alcohol and isonicotinate, IM), concentrations were low or nondetected. After prednisolone 21-sodium succinate (IV), the half-life of elimination (99.5 minutes) was significantly (P less than 0.01) longer than that for dexamethasone. After prednisolone 21-sodium succinate (IM), absorption was rapid and bioavailability was high. After prednisolone acetate (IM), absorption was slow and prednisolone was present in plasma for about 7 days. Due to the nonlinearity of prednisolone kinetics, a bioavailability higher than 100% was obtained. The basal plasma hydrocortisone concentration was approximately 70 ng/ml. After dexamethasone (IV or IM), plasma hydrocortisone values decreased after a 2-hour delay and returned to base line after a 3 to 4 day delay. After prednisolone 21-sodium succinate (IV or IM), plasma hydrocortisone decreased immediately (IV) or rapidly (IM) and returned to base line after a 24-hour delay. After prednisolone acetate (IM), plasma hydrocortisone decreased for up to 21 days.
D000042:Absorption; D000311:Adrenal Glands / Q000187:drug effects*; D000818:Animals; D001682:Biological Availability; D003907:Dexamethasone / Q000031:analogs & derivatives* / Q000378:metabolism*; D003908:Dexamethasone Isonicotinate / Q000378:metabolism* / Q000494:pharmacology; D005260:Female; D006207:Half-Life; D006736:Horses / Q000378:metabolism*; D006854:Hydrocortisone / Q000097:blood; D007700:Kinetics; D008297:Male; D011239:Prednisolone / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology
D003907:Dexamethasone; C009935:prednisolone acetate; D003908:Dexamethasone Isonicotinate; D011239:Prednisolone; C021322:prednisolone hemisuccinate; D006854:Hydrocortisone