Drug Interactions between Haldol and lithium

MONITOR CLOSELY: Haloperidol can cause dose-related prolongation of the QT interval. Theoretically, coadministration with other agents that can prolong the QT interval may result in elevated risk of ventricular arrhythmias, including ventricular tachycardia and torsade de pointes, because of additive arrhythmogenic potential related to their effects on cardiac conduction. Haloperidol treatment alone has been associated with a number of reported cases of torsade de pointes and sudden death. The majority of cases involved intravenous administration or use of higher than recommended dosages. Lithium has also been reported to prolong the QT interval in some patients. In general, the risk of an individual agent or a combination of agents causing ventricular arrhythmia in association with QT prolongation is largely unpredictable but may be increased by certain underlying risk factors such as congenital long QT syndrome, cardiac disease, and electrolyte disturbances (e.g., hypokalemia, hypomagnesemia). In addition, the extent of drug-induced QT prolongation is dependent on the particular drugs involved and dosages of the drugs.

MONITOR CLOSELY: Although haloperidol and lithium have been used safely together in many patients, there have been a few reported cases of encephalopathic syndrome consisting of severe neurotoxic effects and extrapyramidal symptoms, followed by irreversible brain damage, associated with the combination. The mechanism is unknown.

MANAGEMENT: Caution is advised if haloperidol is used in combination with lithium, particularly when administered intravenously (not approved by the FDA) or at higher than recommended dosages. Large doses of both drugs should generally be avoided. Some clinicians have recommended reducing the haloperidol dosage when lithium is initiated. Patients should be followed closely for evidence of neurotoxicity, especially during the first few weeks of therapy. Therapy should be discontinued if potential signs and symptoms of encephalopathic syndrome develop, including weakness, fever, lethargy, tremulousness, confusion, extrapyramidal symptoms, leukocytosis, and elevations in serum enzymes, BUN and fasting blood sugar. In addition, patients should be advised to seek medical attention if they experience symptoms that could indicate the occurrence of torsades de pointes such as dizziness, palpitations, or syncope.

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