Decreased plasma concentrations of imipramine and desipramine following cholestyramine intake in depressed patients.

The effect of cholestyramine (4 g t.i.d. for 5 days) on the steady-state plasma concentrations of imipramine and desipramine was assessed in six depressed patients receiving chronic treatment with imipramine (75-150 mg/day). Compared with baseline, cholestyramine treatment was associated with an average 23% decrease in plasma imipramine levels [from 211 +/- 95 to 159 +/- 67 nmol/L, (mean +/- SD), p < 0.05], whereas desipramine levels decreased only marginally. These data suggest that administration of cholestyramine at therapeutic doses impairs the gastrointestinal absorption of concurrently prescribed imipramine by an extent that is potentially clinically significant.