Influence of body condition on plasma prednisolone and prednisone concentrations in clinically healthy cats after single oral dose administration

Influence of body condition (over-conditioned vs. normal-conditioned) on plasma glucocorticoid concentrations after single dose oral prednisolone or prednisone in 11 cats (5 normal-conditioned and 6-over-conditioned) was investigated using a two-drug crossover trial (3-week washout interval). Body condition was determined using criterion-referenced bioelectrical impedance together with plasma drug concentrations (prednisolone [active drug] and prednisone [pro-drug]) measured by HPLC. Although interconversion of each drug to the other was confirmed, a single 2 mg/kg body weight oral dose of prednisolone produced significantly higher plasma prednisolone concentration (∼4-fold higher AUC) compared to prednisone. Significantly higher plasma drug concentrations in over-conditioned cats (∼2-fold) compared to normal-conditioned cats might explain their perceived increased risk for glucocorticoid associated side effects (hepatic lipidosis, diabetes mellitus). Findings suggest low comparative bioavailability of oral prednisone compared to prednisolone in cats and consideration of lean body mass or ideal body weight for dosing practices.