Table 1

Estimated IC50 values (μM) of orphenadrine and methimazole for different human P450 enzymes

CompoundInhibition Protocol1A22A62B62B61-a2C92C192D62E13A4
OrphenadrineCompetitive≥1000≥1000750180≥1000800150≥1000≥1000
Preincubation≥1000≥1000425250360≥1000110≥1000≥1000
MethimazoleCompetitive 1-b ≥1000100≥1000100≥1000≥1000≥100040
Preincubation 1-b ≥10007≥100088≥1000≥100014
  • 1-a Activity assayed in microsomes containing cDNA-expressed CYP2B6.

  • 1-b Inhibited at low concentrations, but the activities recovered at higher concentrations.