Thioridazine

Pharmacogenomic Information in the Context of the FDA-Approved Drug Label*

Thioridazine is used to treat schizophrenic patients. It has potentially fatal effects on heart rythm and should only be used if other antipsychotic drugs are not effective or cause intolerable side effects. Its use is warned against in people with reduced CYP2D6 activity and hence, reduced clearance of the drug, as that increases the likelihood of the potential fatal effects.

Excerpts from the thioridazine drug label:

"Therefore, thioridazine is contraindicated with these drugs as well as in patients, comprising about 7% of the normal population, who
are known to have a genetic defect leading to reduced levels of activity of P450 2D6."

"Certain circumstances may increase the risk of Torsades de pointes and/or sudden death in association with the use of drugs that
prolong the QTc interval, including 1) bradycardia, 2) hypokalemia, 3) concomitant use of other drugs that prolong the QTc interval,
4) presence of congenital prolongation of the QT interval, and 5) for thioridazine in particular, its use in patients with reduced activity
of P450 2D6 or its coadministration with drugs that may inhibit P450 2D6 or by some other mechanism interfere with the clearance of
thioridazine."

(For the complete drug label text with sections containing pharmacogenetic information highlighted, see the Thioridazine drug label PDF.)