Influence of Long-Term Furosemide Use on Bone Mineral Content, Bone Metabolism Markers, and Water Weight Loss in Horses.

Furosemide is used to reduce the incidence of exercise-induced pulmonary hemorrhage in racehorses. Previous research suggests furosemide negatively impacts calcium balance, which may have long-term implications for bone health. Eleven healthy horses, either control (CON, n = 5) or treatment (FUR, n = 6), were used to test furosemide's effects on bone mineral content (BMC), bone metabolism biomarkers, and weight loss after administration. Treatment horses received IV furosemide at 1 mg⋅kg-1 BW once weekly for seven weeks, and blood was collected before and at 24 hours after administration for biomarker analysis. All horses were weighed before and at 2, 4, 8, 24, and 48 hours after administration. Radiographs of the left third metacarpal were taken every 28 days for BMC determination using radiographic bone aluminum equivalence. After administration, FUR lost more BW than CON (P < .05 for all) as quickly as 2 hours after administration (CON: -0.4 ± 0.3%, FUR: -2.2 ± 0.3%), and these losses remained greater than CON at 4 hours (CON: -1.0 ± 0.3%, FUR: -3.3 ± 0.3%) and 8 hours (CON: 0.0 ± 0.3%, FUR: -1.2 ± 0.3%). FUR lost more BW on day 0 than CON (P = .03), but on day 28 and day 49, FUR BW losses were no greater than CON (P > .10). No treatment effects were observed for BMC nor pyridinoline and osteocalcin concentrations (P > .10). Reduced BW changes over time in FUR but not CON warrant further investigation to establish the efficacy of frequent furosemide administration over long periods of time.