Haloperidol with itraconazole

Adverse effects can result from increased plasma concentrations of haloperidol during itraconazole treatment. This has been observed in 13 schizophrenic patients treated with haloperidol 12 or 24 mg/day who took itraconazole 200 mg/day for 7 days (51). Plasma concentrations of haloperidol were significantly increased and neurological adverse effects were more common. Itraconazole is a potent inhibitor of CYP3A4. 

GFJ has been shown to increase the exposure of carbamazepine (175), cisapride (176-179), fluvoxamine (184), losartan (188), methadone (189), scopolamine (191), and sertraline (192). However, only the interaction of GFJ with carbamazepine and cisapride seems to be clinically relevant. No alteration in exposure was observed for clozapine (180,181), heophylline (195), halo-peridol (196), and omeprazole (190). Reports of increased pharmacokinetic parameters of clozapine, theophylline, and haloperidol suggest that an interaction is unlikely to be clinically relevant. Contradicting results were reported for itraconazole (185-187), digoxin (75,183), and sildenafil (193,194). An increased effect on concomitant use of diclofenac and GFJ was observed in rats (182). Overall, the clinical relevance for this drug class appears to be low. 

Clinically important, potentially hazardous interactions with amiodarone, astemizole, bepridil, carbamazepine, chloroquine, cisapride, clarithromycin, dihydroergotamine, disopyramide, ergotamine, grapefruit juice, halofantrine, haloperidol, itraconazole, ketoconazole, methadone, moxifloxacin, phenobarbital, phenytoin, pimozide, procainamide, quinidine, rifampicin, ritonavir, sotalol, St John s wort, telithromycin, terfenadine, voriconazole... 

The clinical significance of the raised levels is unclear, although one study found an increase in neurological adverse effects with haloperidol. It may be prudent to monitor concurrent use, decreasing the haloperidol or bromperidol dose if adverse effects become troublesome. This interaction may be of more importance in those patients have less active CYP2D6, the predominant isoenzyme involved in the metabolism of haloperidol, as CYP3A4, which is inhibited by itraconazole, will then become more important. It is likely that other azoles that are potent inhibitors of CYP3A4, such as ketoconazole, would interact similarly, but this needs confirmation. 

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