Table 1

Influence of quinidine on metabolism of meloxicam, testosterone, and nifedipine by human liver microsomes and recombinant human CYPs

SubstrateSubstrate ConcentrationActivatorActivator ConcentrationControl
μM μM %
CYP 2C9Meloxicam10100
CYP 2C9Meloxicam10Quinidine10110
CYP 2C9Meloxicam10Quinidine10060
CYP 3A4Meloxicam10100
CYP 3A4Meloxicam10Quinidine10160
CYP 3A4Meloxicam10Quinidine100510
CYP 3A4Testosterone50100
CYP 3A4Testosterone50Quinidine10120
CYP 3A4Testosterone50Quinidine10060
CYP 3A4Nifedipine200100
CYP 3A4Nifedipine200Quinidine1030
CYP 3A4Nifedipine200Quinidine10010

Values were corrected for basic activity (0.14 pmol/min/mg protein) of control microsomes not expressing CYP 3A4 or CYP 2C9 (mean of duplicate to triplicate experiments).