Effects of multiple intramuscular injections and doses of dexamethasone on plasma cortisol concentrations and adrenal responses to ACTH in horses.

This research observes the effects of varying doses and multiple injections of dexamethasone on the adrenal response in horses. It was found that both commonly used dosages caused a suppression of adrenocortical activity, but normal ACTH responses were observed after a sustained injection regime.

Research Methodology

• The research began by administering multiple Intramuscular (IM) doses of dexamethasone to horses, to monitor the duration of adrenocortical suppression and insufficiency.
• Two commonly used dosages of dexamethasone (0.044 and 0.088 mg/kg of body weight) were used in the study.
• Dexamethasone was administrated at 5-day intervals for a total of six injections.
• Daily blood samples were collected from the horses and the plasma portion was frozen and later tested for cortisol levels.

Findings

• Maximum suppression of plasma cortisol was observed in horses given both dosages of dexamethasone.
• It was found that the plasma cortisol concentrations returned to their baseline values in all the horses by 4 days after the dexamethasone injection.
• There was no measurable adrenal atrophy despite the six dexamethasone injections given at 5-day intervals. This was evident through the normal ACTH (which stimulates the adrenal glands) responses.

Conclusion

• The study therefore concludes that although the dexamethasone doses caused an initial suppression of adrenocortical activity, the horses’ bodies were able to revert to normal cortisol levels within 4 days of each dexamethasone injection.
• The study also found no adverse effects on the adrenal glands’ response to ACTH stimulation. This suggests that under the conditions this study administered, the use of dexamethasone does not seem to cause long-term damage to the horses’ adrenal ability.