ADDITIVE DEPRESSANT EFFECT WITH SEDATIVES, HYPNOTICS, ANTIHISTAMINES, OPIATES AND ALCOHOL. WHEN USED CONCOMITANTLY, ABOUT 1/4 TO 1/2 THE USUAL DOSAGE OF SUCH AGENTS IS REQUIRED. POTENTIATION OF ANTICHOLINERGIC EFFECTS OF ANTIPARKINSON AGENTS. ADDITIVE ORTHOSTATIC HYPOTENSIVE EFFECT WITH MAOI. REVERSES ANTIHYPERTENSIVE EFFECT OF GAUENTHIDINE, METHYLDOA AND CLONIDINE. INCREASED RISK OF ARRHYTHMIAS WITH ANTIMALARIALS, TRICYCLIC ANTIDEPRESSANTS, ANTIHISTIMINES AND CISAPRIDE. NEUROLEPTIC DRUGS ELEVATE PROLACTIN LEVELS. CHLORPROMAZINE DIMINISHES THE EFFECT OF ORAL ANTICOAGULANTS. PHENOTHIAZINES CAN PRODUCE ALPHA-ADRENERGIC BLOCKADE.
THIORIDAZINE MAY LOWER THE CONVULSIVE THRESHOLD; DOSAGE ADJUSTMENTS OF
ANTICONVULSANTS MAY BE NECESSARY. THIORIDAZINE MAY INTERFERE WITH
THE METABOLISM OF DILANTIN AND THUS PRECIPITATE DILANTIN TOXICITY. CONCOMITANT ADMINISTRATION WITH PROPRANOLOL RESULTS IN INCREASED PLASMA LEVELS OF BOTH DRUGS. THIAZIDE DIURETICS MAY ACCENTUATE THE ORTHOSTATIC HYPOTENSION THAT MAY OCCUR WITH PHENOTHIAZINES. THE PRESENCE OF PHENOTHIAZINES MAY PRODUCE FALSE- POSITIVE PHENYLKETONURIA (PKU) TEST RESULTS. METABOLISM OF THIORIDAZINE IS MEDIATED BY CYTOCHROME P450 ISOENZYME CYP2D6; THIORIDAZINE ITSELF IS ALSO INHIBITOR OF THE ENZYME. THEREFORE THERE IS POTENTIAL FOR INTERACTION BETWEEN THIORIDAZINE AND OTHER DRUGS THAT INHIBIT OR ACT AS A SUBSTRATE FOR THIS ENZYME; SUCH DRUGS SHOULD NOT BE GIVEN WITH THIORIDAZINE. SOME OF THESE ARE ANTIARRHYTHMICS, SSRIS AND TRICYCLIC ANTIDEPRESSANTS, CERTAIN ANTIPSYCHOTICS, BETABLOCKERS, HIV-PROTEASE INHIBITORS, & OPIATES. CONCOMITANT ADMINISTRATION WITH DRUGS THAT CAUSE PROLONGATION OF Q-T INTERVAL IS ALSO NOT RECOMMENDED.