Interactions between smectite, a mucus stabilizer, and acidic and basic drugs. In vitro and in vivo studies.

The interaction of phenylbutazone and diazepam with smectite were studied in in-vivo and in-vitro. The kinetics of both drugs were investigated in healthy subjects after oral administration as monotherapy or in association with smectite. Smectite did not substantially alter the kinetics of phenylbutazone, whereas the peak plasma concentration of diazepam was reduced to 91%, and the time of peak concentration was prolonged by 153% of the control values. The in-vitro investigations were conducted at pH 5.5 and 8 and showed that there was no interaction between phenylbutazone and smectite, but that it adsorbed diazepam. The findings suggest that smectite delays the absorption of basic drugs and does not alter the absorption kinetics of acidic drugs.