Pharmacokinetics of diclofenac after oral administration of its potassium salt in sachet and tablet formulations

This paper reports the results of a pharmacokinetic study involving 24 heal thy volunteers and designed to characterise the rate and extent of diclofen ac absorption after the administration of a single dose of diclofenac (CAS 15301-86-5) potassium salt 50 mg in sachet (Voltfast(R)) and tablet (Catafl am(R)) formulations, Timed plasma concentrations of diclofenac during a 12-h-period after dosing were measured by means of HPLC with UV detection at 275 nm and a quantific ation limit of 10 ng/ml; the method was fully validated for pharmacokinetic purposes. These plasma concentrations were used to calculate C-max, t(max) , trapezoidal AUC(0-t) and AUC(0-x) and t(1/2) by means of noncompartmental analysis C-max and t(max) are the parameters expressing the rate of absorp tion, wehreas the AUCs reflect the extent of absorption. The rate of absorp tion with the sachets proved to be very fast, reaching peak values at 10 mi n in seven subjects and at 15 min in the remaining subjects: mean lime was 13.68 min, with concentrations at 5 min being 38 % of C-max. The average ti me to peak concentration with the tablets was 53.10 min. The extent of abso rption of the sachets and tablets was similar with AUC(0-x), values of resp ectively 1362 and 1214 ng . ml(-1) . h, and a 90 % confidence interval 1.05 -1.20. The highly soluble potassium salt of diclofenac was rapidly absorbed, espec ially in its sachet formulation, and thus appears to be an invaluable analg esic agent that is particularly useful for quick pain relief.