Abstract
Two clinical studies were conducted to study the pharmacokinetics of alclofenac in healthy adult male volunteers when the drug was administered in both single and multiple dosing regimens. The first study involved the participation of thirty-two subjects, each of whom received single 500 mg and 1000 mg oral doses of alclofenac, using a complete crossover experimental design. The second study involved the participation of sixteen subjects, eight of whom received a 500 mg dose, and eight of whom received a 1000 mg dose of alclofenac every eight hours for ninety-six consecutive hours (four days) with no crossover.
In the first study, plasma alclofenac levels were monitored for ten hours post-dosing, while in the second study, drug levels were monitored for four and one-half days (i.e. through twelve hours after the last dose).
Initially, using the programme NONLIN, single dose data were fit to a bi-exponential equation, with output from these fits serving as initial estimates for a second fit to the same equation. The results of these second fits were then used as initial estimates to fit the multiple dosing data to a multiple dosing one-compartment model with first order absorption and elimination. Finally, all sets of data were simultaneously fit to the one-compartment open model, with both single and multiple dosing, in an attempt to obtain a uniform interpretation, with a single set of parameters that would adequately describe the plasma alclofenac levels to be expected with a variety of dosing regimens.
It was found that the kinetics did not significantly change upon going from single to multiple dosing, and that with the exception of the apparent absorption rate constant, a single set of parameters adequately described all the data collected. The rate of absorption seemed to be somewhat dose-dependent at these levels, being slower after 1000 mg doses than after 500 mg doses. For this reason, the simultaneous fitting program was allowed to estimate different absorption rate constants for the 500 mg and 1000 mg doses. The results of these simultaneous analyses were:
Vol Distribution/Fraction Abs = 6.56 Litres Absorption Half-Life (500 mg) = 14 Minutes Absorption Half-Life (1000 mg) = 30 Minutes Elimination Half-Life = 2.1 Hours Absorption Lag Time = 14 Minutes
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