Haloperidol lactate injection

Drug Interactions Drug-drug interactions can be pharmacodynamic (combined pharmacologic effects) or pharmacokinetic (alteration of plasma levels). The risks of using haloperidol in combination with other drugs have been evaluated as described below. Pharmacodynamic Interactions Since QTc interval-prolongation has been observed during haloperidol treatment, caution is advised when prescribing to a patient with QT-prolongation conditions or to patients receiving medications known to prolong the QTc-interval (see WARNINGS, Cardiovascular Effects ).

Examples include (but are not limited to): Class 1A antiarrhythmics (e.g., procainamide, quinidine, disopyramide); Class 3 antiarrhythmics (e.g., amiodarone, sotalol); and other drugs such as citalopram, erythromycin, levofloxacin, methadone, and ziprasidone. Caution is advised when haloperidol is used in combination with drugs known to cause electrolyte imbalance (e.g., diuretics or corticosteroids because hypokalemia, hypomagnesemia, and hypocalcemia are risk factors for QT prolongation. Haloperidol may impair the antiparkinson effects of levodopa and other dopamine agonists.

If concomitant antiparkinson medication is required, it may have to be continued after haloperidol is discontinued because of the difference in excretion rates. If both are discontinued simultaneously, extrapyramidal symptoms may occur. The physician should keep in mind the possible increase in intraocular pressure when anticholinergic drugs, including antiparkinson agents, are administered concomitantly with haloperidol. As with other antipsychotic agents, it should be noted that haloperidol may be capable of potentiating CNS depressants such as anesthetics, opioids, and alcohol.

Pharmacokinetic Interactions Drugs that May Increase Haloperidol Plasma Concentrations Haloperidol is metabolized by several routes. The major pathways are glucuronidation and ketone reduction. The cytochrome P450 enzyme system is also involved, particularly CYP3A4 and, to a lesser extent, CYP2D6. Inhibition of these routes of metabolism by another drug or a decrease in CYP2D6 enzyme may result in increased haloperidol concentrations. The effect of CYP3A4 inhibition and of decreased CYP2D6 enzyme activity may be additive. The haloperidol plasma concentrations increased when a CYP3A4 and/or CYP2D6 inhibitor was coadministered with haloperidol.

Examples include: • CYP3A4 inhibitors – alprazolam; itraconazole, ketoconazole, nefazodone, ritonavir. • CYP2D6 inhibitors – chlorpromazine; promethazine; quinidine; paroxetine, sertraline, venlafaxine. • Combined CYP3A4 and CYP2D6 inhibitors – fluoxetine, fluvoxamine; ritonavir. • Buspirone. Increased haloperidol plasma concentrations may result in an increased risk of adverse events, including QTc interval prolongation (see WARNINGS – Cardiovascular Effects ). Increases in QTc have been observed when haloperidol was given with a combination of the metabolic inhibitors ketoconazole (400 mg/day) and paroxetine (20 mg/day).

It is recommended that patients who take haloperidol concomitantly with such medicinal products be monitored for signs or symptoms of increased or prolonged pharmacologic effects of haloperidol, and the haloperidol dose be decreased as deemed necessary. Valproate: Sodium valproate, a drug known to inhibit glucuronidation, does not affect haloperidol plasma concentrations. Drugs that May Decrease Haloperidol Plasma Concentrations Coadministration of haloperidol with potent enzyme inducers of CYP3A4 may gradually decrease the plasma concentrations of haloperidol to such an extent that efficacy may be reduced.

Examples include (but are not limited to): carbamazepine, phenobarbital, phenytoin, rifampin, St John’s Wort ( Hypericum, perforatum ). Rifampin: In a study of 12 patients with schizophrenia coadministered oral haloperidol and rifampin, plasma haloperidol levels were decreased by a mean of 70% and mean scores on the Brief Psychiatric Rating Scale were increased from baseline. In 5 other patients with schizophrenia treated with oral haloperidol and rifampin, discontinuation of rifampin produced a mean 3.3-fold increase in haloperidol concentrations.

Carbamazepine: In a study in 11 patients with schizophrenia coadministered haloperidol and increasing doses of carbamazepine, haloperidol plasma concentrations decreased linearly with increasing carbamazepine concentrations. During combination treatment with inducers of CYP3A4, it is recommended that patients be monitored and the haloperidol dose increased as deemed necessary. After withdrawal of the CYP3A4 inducer, the concentration of haloperidol may gradually increase and therefore it may be necessary to reduce the dose of haloperidol. Effect of Haloperidol on Other Drugs Haloperidol is an inhibitor of CYP2D6.

Plasma concentrations of CYP2D6 substrates (e.g., tricyclic antidepressants such as desipramine or imipramine) may increase when they are co-administered with haloperidol. Information for Patients Haloperidol may impair the mental and/or physical abilities required for the performance of hazardous tasks such as operating machinery or driving a motor vehicle. The ambulatory patient should be warned accordingly. The use of alcohol with this drug should be avoided due to possible additive effects and hypotension.

Pregnancy ). Other Haloperidol should be administered cautiously to patients: • with severe cardiovascular disorders, because of the possibility of transient hypotension and/or precipitation of anginal pain. Should hypotension occur and a vasopressor be required, epinephrine must not be used since haloperidol may block its vasopressor activity and paradoxical further lowering of the blood pressure may occur. Instead, metaraminol, phenylephrine or norepinephrine should be used. • receiving anticonvulsant medications, with a history of seizures, or with EEG abnormalities, because haloperidol may lower the convulsive threshold.

If indicated, adequate anticonvulsant therapy should be concomitantly maintained. • with known allergies, or with a history of allergic reactions to drugs. • receiving anticoagulants, since an isolated instance of interference occurred with the effects of one anticoagulant (phenindione). When haloperidol is used to control mania in cyclic disorders, there may be a rapid mood swing to depression. Severe neurotoxicity (rigidity, inability to walk or talk) may occur in patients with thyrotoxicosis who are also receiving antipsychotic medication, including haloperidol.

Nursing Mothers Since haloperidol is excreted in human breast milk, infants should not be nursed during drug treatment with haloperidol.