Non-CYP metabolism. Absence of reported interactions with CYP-metabolised drugs indicate lack of capacity for CYP-induction or CYP-inhibition. However, side effects such as nausea and vomiting may be potentially porphyrinogenic through reduction in caloric intake.

Tioguanine is an analogue of the naturally occurring purine, guanine.

Tioguanine is an antineoplastic agent used in the induction of remissions in acute myeloid leukaemia. It has also been used in other malignancies including acute lymphoblastic leukaemia and chronic myeloid leukaemia. Tioguanine is given orally. Common adverse reactions of tioguanine that can be confused with an acute porphyric attack are nausea and vomiting. Side effects such as nausea and vomiting may be potentially porphyrinogenic through reduction in caloric intake.

Tioguanine is inactivated primarily by methylation to aminomethylthiopurine; small amounts are deaminated to thioxanthine, and may go on to be oxidised by xanthine oxidase to thiouric acid, but inactivation is essentially independent of xanthine oxidase and is not affected by inhibition of the enzyme. Oxidative S-demethylation may involve CYPs. There ar two main catabolic ways, none of which is CYP-dependent: methylation and deamination followed by oxidation. No observations of interactions with CYP-metabolism of other drugs. Not listed as CYP-inducer or inhibitor.

Used uneventfully in the treatment of acute myelogenous leucemia in an AIP woman (Wehmeier, 1987). Used uneventfully in the treatment of acute lymphoblastic leukaemia in VP woman (Samuels, 1984).