Substrate of several CYPs, including 3A4. Potent CYP 3A4 inhibitor. Autoactivator of CYP 2B6, probably quantitatively insignificant. Some clinical experience of tolerance. Two references state (probable) non-porphyrinogenicity.

Verapamil / norverapamil: Phenylalkylamine derivatives with calcium antagonistic action. Metabolized by CYPs 2C8, 3A4, 3A5, 2C9, 2E1, 1A2, 2B6, 2C19. Inhibitor of CYPs 2C8, 1A2, 2C9, 3A4 (potent) 2D6, 2C19. Autoactivator of CYP 2B6. MFM James, RJ Hift. Porphyrias. Br J Anaesth 2000; 85, 143-53: use with care. Thunell, patient report (n=2): tolerated. Andersson, patient reports: tolerated (n=4). South African list: use with care French list: use. Kauppinen and Mustajoki. Prognosis of acute porphyria: Occurrence of acute attacks, precipitating factors,and assocciated diseases. Medicine 1992; 71, 1-13 : tolerated (n=1).

Uneventful use reported in 4 patients with acute porphyria.