Background: Hyperinsulinemia associated with pituitary pars intermedia dysfunction (PPID) and/or equine metabolic syndrome is well documented to put horses at high risk of laminitis. While dietary control of simple sugars and starch is the most effective therapy to control hyperinsulinemia, some horses fail to respond.
Case descriptions: Ten horses with hyperinsulinemia refractory to diet control, metformin, levothyroxine, and pergolide (if diagnosed with PPID) were treated with sodium-glucose cotransporter-2 inhibitor canagliflozin (Invokana®). Nine horses were hyperglycemic (>5.5 mmol/l) or had a history of hyperglycemia. Before instituting therapy, renal function was assessed by determining serum creatinine and blood urea nitrogen concentrations. Canagliflozin was administered orally once a day, with food. Dipstick urinalysis was performed every 2 weeks to confirm glucosuria and screen for proteinuria. Owners were also instructed regarding clinical signs consistent with urinary tract infection. All horses responded with a substantial decrease in serum insulin concentrations to normal or near normal values. Laminitis pain resolved in all cases, with regression of fat deposits. Owner satisfaction with outcomes was 100%.
Conclusion: Once daily administration of the SGLT2 inhibitor canagliflozin corrected hyperglycemia, reduced insulin to normal or near normal levels, and was 100% effective in reversing or reducing abnormal fat pads and eliminating laminitis pain in horses with refractory hyperinsulinemia and laminitis. The core aspects of therapy-diet control, exercise when possible, and adequate treatment of PPID-must also be maintained if using canagliflozin. Canagliflozin should be reserved for refractory cases. Further controlled trials to investigate canagliflozin pharmacokinetics, pharmacodynamics, efficacy, and safety are needed.
Keywords: Canagliflozin; Horses; Hyperinsulinemia; Laminitis; Metformin.