Recovery of insulin sensitivity in mature horses after a 3 week course of dexamethasone therapy

Reasons for performing the study: Dexamethasone is an anti-inflammatory drug commonly used in equine medicine. Insulin sensitivity decreases with prolonged dexamethasone administration, but little information is available about the duration of this side effect after long-term treatment ends. Objectives: To determine how long it takes for blood glucose, insulin and markers of insulin sensitivity to return to normal ranges after extended dexamethasone treatment has ceased. Study design: Experimental study. Methods: Eight healthy, mature, mixed-breed horses received 0.04mg/kg bwt/day oral dexamethasone for 21 days. Blood samples were taken weekly during dexamethasone treatment (Days -21, -14 and -7). Following the final dose of dexamethasone on Day 0, blood samples were taken on Days 1-6, 8, 10, 12, 15 and 22. Day -21 represents baseline or normal blood predexamethasone. Results: On Day 1, plasma glucose and insulin concentrations and the modified insulin-to-glucose ratio (a proxy for pancreatic β cell responsiveness) were higher and the reciprocal of the square root of insulin (a proxy for the estimate of insulin sensitivity) was lower, in comparison with Day -21 values. Blood glucose concentrations dropped and returned to Day -21 values by Day2. Insulin concentrations remained elevated until Day3. Values for the modified insulin-to-glucose ratio decreased and returned to Day -21 concentrations by Day4. Values for the reciprocal of the square root of insulin did not return to Day -21 values until Day15. Conclusions: These results indicate that, in contrast to blood glucose concentrations, which return to normal quickly (within 2 days after treatment ends), the pancreatic insulin-secreting response has a delayed recovery.