Only metabolised to a minor extent. Unspecific CYP-inhibitor (CYPs 2C9, 11B1, 1A2, 2C19, 2D6, 2E1, 3A4). To be observed: imidazole is an CYP 2E1 inducer! Several references consider it safe or probably safe. Also repeatedly used without porphyric side effects.

(To be edited, initial data ST OCT 04) Imidazole histamine-receptor antagonist used in ventricular hyperacidity. Slightly (10-15 %) metabolized enzymatically to sulfdioxide. In large parts excreted unchanged in urine. Unspecific CYP-inhibitor which has been used in the treatment of the acute porphyric attack. MFM James, RJ Hift. Porphyrias. Br J Anaesth 2000; 85, 143-5: use with care South African list: use with care. French list: authorized. Merck Index: safe. Siepmann M et al. Cimetidine in treatment of acute intrmittent porphyria. Z Gastroenterol. 31:246, 1993: safe. D.Andersson: Frequently used without porphyric side effects. C.Andersson; patient reports: tolerated (n=2)

Uneventful use reported in 3 patients with acute porphyria.