Dexamethasone and prednisolone in the horse: pharmacokinetics and action on the adrenal gland.

The research is focused on examining the pharmacokinetics and how dexamethasone and prednisolone influence the adrenal gland in horses. This involves studying their effects, how they’re absorbed and eliminated, and their bioavailability in the body.

Methodology

• The study involved six horses, all of which were administered different forms and methods of the two drugs; dexamethasone alcohol was given intravenously (IV) or intramuscularly (IM), and prednisolone either in the form of 21-sodium succinate IV or IM, or prednisolone acetate IM.
• The concentration of these drugs in the horses’ plasma was determined using a high-performance liquid chromatographic method, a technique used for separating mixtures of compounds in scientific experiments.

Results

• The study found that the half-life – the rate at which a drug is removed from the body – of dexamethasone, whether in alcohol or 21-isonicotinate forms, was similar (53 minutes) for both methods of administration (IV and IM). However, it was found that the drug’s concentrations were low or non-detectable when administered via IM.
• On the other hand, prednisolone’s half-life was longer, specifically 99.5 minutes when administered as 21-sodium succinate IV. Interestingly, this was found to be significantly longer than that for dexamethasone.
• The study also noted that the rapid absorption and high bioavailability of prednisolone 21-sodium succinate when administered IM, as well as its continued presence in the plasma for about seven days when administered as prednisolone acetate. Due to the nonlinearity of prednisolone kinetics, a bioavailability higher than 100% was obtained.
• Moreover, the impact of both drugs on the concentration of hydrocortisone – a corticosteroid hormone produced by the adrenal gland – in the plasma was monitored. After being administered dexamethasone (either IV or IM), plasma hydrocortisone values fell after a delay of 2 hours and returned to baseline levels after a delay of 3 to 4 days. 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. With prednisolone acetate (IM), plasma hydrocortisone fell for up to 21 days.

Significance

• The research contributes important knowledge about the pharmacokinetics of dexamethasone and prednisolone and their impacts on the adrenal gland in horses, information that could be essential for the correct administration of these drugs in veterinary medicine.
• It also hints at the discrepancies between the half-lives of the two drugs and the manner of their administration, which can influence their absorption and bioavailability in horses. This is especially pertinent for prednisolone, which was found to remain in the system for up to seven days.