Methodology of kinetic interaction studies in clinical pharmacology: an experimental contribution on diftalone and acetylsalicylic acid.

The possible interaction of acetylsalicylic acid (ASA) and diftalone (DIF), a new anti-inflammatory drug, was studied in 6 volunteers. All subjects received each of the following three treatments: ASA 1 g, DIF 0.5 g, ASA 1 g plus DIF 0.5 g at 4-day intervals (stage 1 of the study). In stage II of the same study, each subject received ASA 1 g plus DIF 0.5 g in three different occasions 1 week apart; after a 7-day pre-treatment with either DIF 0.25 g b.i.d., or ASA 0.5 g b.i.d., or DIF 0.25 g b.i.d. plus ASA 0.5 g b.i.d. A total of four different comparisons were made. After pre-treatment with DIF, but not after pre-treatment with DIF plus ASA, the peak level of salicylate was significantly reduced by about 15%. No other evidence of interaction was found.