Oxidationen reguleres primært af cytochrom P450 isoenzym 2B6 og 3A4 og i mindre grad af 1A1, 1A2 og 2C19.
The oxidative step is regulated primarily by Cytochrome P450 isoenzymes 2B6 and 3A4 and to a lesser extent by 1A1, 1A2 and 2C19.