1. The disposition of ketoprofen enantiomers was studied in 21 patients taking racemic ketoprofen (Orudis SR). 2. In each patient the plasma concentrations of the R‐ and S‐enantiomers were similar at all times over a 24 h dosing interval. The mean (+/‐ s.e. mean) time‐averaged plasma ketoprofen concentrations over the dosage interval were 0.76 (+/‐ 0.06) mg l‐1 for R‐ketoprofen and 0.78 (+/‐ 0.06) mg l‐1 for S‐ ketoprofen. 3. Creatinine clearances for the 21 patients ranged from 6‐ 162 ml min‐1. There was no correlation between creatinine clearance and time‐averaged plasma concentration for either R‐ or S‐ketoprofen. 4. Approximately 30% of the dose was recovered in urine (unconjugated + glucuronide conjugate) and this was made up of 43% R‐ketoprofen and 57% S‐ketoprofen. Because of incomplete urine recoveries of ketoprofen it was not possible to determine whether inversion from the R‐ to the S‐ enantiomer takes place in man. 5. The data suggest that in terms of total (bound + unbound) ketoprofen, half the concentration value derived by a non‐enantiospecific analysis would give a reasonable approximation of the pharmacologically active S‐enantiomer concentration in plasma.

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5042The disposition of prednisolone has been studied in eight male subjects with and without the concomitant administration of cortisol which produced plasma cortisol concentrations 10-fold higher than endogenous levels. The clearance and steady-state distribution volume of total prednisolone were increased as was the prednisolone free fraction but the clearance of unbound prednisolone was unaltered by cortisol co-administration.