Comparison of polydipsia and polyuria in dogs treated with once‐daily or divided twice‐daily oral prednisolone in 12 dogs

OBJECTIVES: To compare the prevalence and severity of polyuria and polydipsia in dogs receiving once-daily or divided-daily oral prednisolone regimens. MATERIALS AND METHODS: In a randomised, crossover trial, 12 client-owned dogs with diseases requiring oral prednisolone were treated with a daily dose ≥1.5 mg/kg, administered once-daily or divided-daily. The initial dosing regimen was administered for 14 days and then switched to the alternative regimen for an additional 14 days. Daily water intake, urine specific gravity and urine osmolality were measured before treatment and on days 7, 14, 21 and 28. RESULTS: The median daily dose of prednisolone administered to dogs was 1.7 mg/kg (range: 1.5 to 2.1 mg/kg). Nine and six dogs experienced polydipsia and diluted urine (likely polyuria), respectively, without difference between once-daily and divided-daily regimens. Dogs treated with a once-daily regimen exhibited significantly lower water intake on day 14 compared to those treated with divided-daily prednisolone. Median urine specific gravity and urine osmolality did not differ between once-daily and divided-daily prednisolone administration. An almost linear positive correlation was established between urine specific gravity and osmolality. CLINICAL SIGNIFICANCE: Once-daily rather than divided-daily dosing is a reasonable option in dogs treated with oral prednisolone to reduce excessive water intake in the clinical setting. Urine specific gravity and osmolality can be used interchangeably for the assessment of urine concentration.