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.

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.