HALOPERIDOL DECANOATE Drug Interactions: What You Need to Know

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 decanoate 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. 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 Decanoate 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 decanoate 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 decanoate dose increased or the dosage interval adjusted, 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 decanoate, or adjust the dosage interval. 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.

CONTRAINDICATIONS Since the pharmacologic and clinical actions of haloperidol decanoate injection, 50 mg /mL and haloperidol decanoate injection, 100 mg/mL are attributed to haloperidol, USP as the active medication, Contraindications, Warnings, and additional information are those of haloperidol, USP, modified only to reflect the prolonged action. Haloperidol is contraindicated in patients with: Severe toxic central nervous system depression or comatose states from any cause. Hypersensitivity to this drug – hypersensitivity reactions have included anaphylactic reaction and angioedema (see WARNINGS, Hypersensitivity Reactions and ADVERSE REACTIONS). Parkinson's disease (see WARNINGS, Neurological Adverse Reactions in Patients with Parkinson's Disease or Dementia with Lewy Bodies). Dementia with Lewy bodies (see WARNINGS, Neurological Adverse Reactions in Patients with Parkinson's Disease or Dementia with Lewy Bodies).

AND PRECAUTIONS

• Sudden Death, Torsades de Pointes (TdP), and QTc Interval Prolongation : Avoid use of haloperidol decanoate in patients who are at risk of developing TdP. Avoid concomitant use of haloperidol decanoate with drugs that may increase risk of QTc interval prolongation or increase haloperidol exposure. Obtain ECG and serum electrolytes at baseline and during treatment as clinically indicated ( 5.2 ).
• Tachycardia and Hypotension: Monitor orthostatic vital signs ( 5.3 ).
• Cerebrovascular Adverse Reactions Including Stroke in Elderly Patients with Dementia-Related Psychosis: Use with caution in patients with schizophrenia who have risk factors for cerebrovascular adverse reactions ( 5.4 ).
• Tardive Dyskinesia : Discontinue treatment if clinically appropriate ( 5.5 ).
• Neuroleptic Malignant Syndrome (NMS) : Immediately discontinue and monitor closely ( 5.6 ).
• Seizures : Haloperidol decanoate is generally not recommended in patients receiving antiseizure drugs or who have a history of seizures or EEG abnormalities. If clinically, indicated, maintain patients taking haloperidol decanoate on adequate antiseizure therapy ( 5.8 ).
• Potential for Cognitive and Motor Impairment: Advise patients to not drive a motor vehicle or operate hazardous machinery until they are reasonably certain haloperidol decanoate does not impair their cognitive and motor functions ( 5.11 ).
• Risk of Encephalopathic Syndrome with Concomitant Use of Lithium : Monitor closely for early signs of neurological toxicity and discontinue haloperidol decanoate if such signs appear ( 5.12 ).
• Leukopenia, Neutropenia, and Agranulocytosis : Perform complete blood counts (CBC) in patients with pre-existing low white blood cell count (WBC) or history of leukopenia or neutropenia. Consider discontinuing haloperidol decanoate if clinically significant decline in WBC occurs in absence of other causative factors. Discontinue haloperidol decanoate in patients with clinically significant neutropenia or an absolute neutrophile count of <1,000/mm 3 ( 5.13 ).
• Hyperprolactinemia: Elevated prolactin levels may occur during acute and chronic use ( 5.14 ).

5.1 Increased Mortality in Elderly Patients with Dementia-Related Psychosis Elderly patients with dementia-related psychosis treated with antipsychotic drugs are at an increased risk of death. In an analysis of 17 placebo-controlled trials (modal duration of 10 weeks), largely in patients taking atypical antipsychotic drugs, the risk of death in antipsychotic drug-treated patients was 1.6 to 1.7 times the risk of death in placebo-treated patients. Over the course of a typical 10-week controlled trial, the incidence of death in antipsychotic drug-treated patients was about 4.5%, compared to an incidence of about 2.6% in placebo-treated patients. Although the causes of death were varied, most of the deaths appeared to be either cardiovascular (e.g., heart failure, sudden death) or infectious (e.g., pneumonia) in nature. Haloperidol decanoate is not approved for the treatment of patients with dementia-related psychosis <span class="opacity-50 text-xs">[see Indications and Usage ( 1 )]</span>.

5.2 Sudden Death, Torsades de Pointes, and QTc Interval Prolongation Cases of sudden death, torsades de pointes (TdP) and QTc interval prolongation have been reported in haloperidol-treated patients <span class="opacity-50 text-xs">[see Adverse Reactions ( 6.1 , 6.2 )]</span>. Cases have been reported even in the absence of predisposing factors. Higher than recommended haloperidol dosages were associated with a higher risk of TdP and QTc interval prolongation. Avoid use of haloperidol decanoate in patients who are at significant risk of developing TdP including those with congenital long QT syndrome, uncontrolled or significant cardiac disease, recent myocardial infarction, ischemic cardiomyopathy, unstable angina, bradyarrhythmias, uncontrolled hypertension, high degree atrioventricular block, severe aortic stenosis, or uncontrolled hypothyroidism. Avoid the concomitant use of haloperidol decanoate with drugs that may increase the risk of the QTc interval prolongation or increase haloperidol exposure. Assess the QTc interval via an ECG at baseline, and during treatment as clinically indicated. Obtain serum electrolytes (including potassium, calcium, phosphorus, and magnesium) at baseline and during treatment as clinically indicated, and correct electrolyte abnormalities.

5.3 Tachycardia and Hypotension Tachycardia and hypotension (including orthostatic hypotension) have been reported in patients treated with haloperidol <span class="opacity-50 text-xs">[see Adverse Reactions ( 6.1 )]</span>. Orthostatic vital signs should be monitored in patients who are at risk for hypotension (e.g., geriatric patients, patients with dehydration, hypovolemia, and concomitantly treated with antihypertensive medications), patients with known cardiovascular disease (history of myocardial infarction, ischemic heart disease, heart failure, or conduction abnormalities), and patients with cerebrovascular disease. Should hypotension occur and a vasopressor be required, epinephrine must not be used since haloperidol decanoate may block its vasopressor activity, and paradoxically lower blood pressure. Instead, metaraminol, phenylephrine or norepinephrine should be used.

5.4 Cerebrovascular Adverse Reactions Including Stroke in Elderly Patients with Dementia-Related Psychosis In placebo-controlled trials, elderly patients with dementia-related psychosis treated with antipsychotics had an increased risk of cerebrovascular adverse reactions (e.g., stroke, transient ischemic attack) including fatalities, compared to those treated with placebo. The mechanism for this increased risk is not known. Haloperidol decanoate is not approved for the treatment of patients with dementia-related psychosis. Haloperidol decanoate should be used with caution in patients with schizophrenia who have risk factors for cerebrovascular adverse reactions.

5.5 Tardive Dyskinesia Tardive dyskinesia (TD) may develop in patients treated with antipsychotic drugs, including haloperidol decanoate <span class="opacity-50 text-xs">[see Adverse Reactions ( 6.1 )]</span>. TD can develop after a relatively brief treatment period at low dosages and may also occur after discontinuation of treatment. If antipsychotic treatment is discontinued, TD may partially or completely remit. Antipsychotic treatment, however, may suppress or partially suppress the signs and symptoms of TD and may mask the underlying process. The effect that symptomatic suppression has upon the long-term course of TD is unknown. The TD risk in patients treated with antipsychotic drugs appears to be highest among the elderly, especially elderly women, but it is not possible to predict, which patients are likely to develop TD. The TD risk and the likelihood that TD will become irreversible increase with the duration of antipsychotic drug treatment and the cumulative dosage. In patients who require chronic antipsychotic treatment, use the lowest dosage and the shortest duration of treatment that produces a satisfactory clinical response. Periodically reassess the need for continued treatment. If signs and symptoms of TD appear in haloperidol decanoate-treated patients, consider drug discontinuation. However, some patients may require haloperidol decanoate treatment despite the presence of TD.

5.6 Neuroleptic Malignant Syndrome Neuroleptic Malignant Syndrome (NMS), a potentially fatal symptom complex, has been reported in association with the use of antipsychotic drugs <span class="opacity-50 text-xs">[see Adverse Reactions ( 6.1 )]</span>. Clinical manifestations of NMS are hyperpyrexia, muscle rigidity, delirium, and autonomic instability, and additional signs may include elevated creatine phosphokinase, myoglobinuria (rhabdomyolysis), and acute renal failure. If NMS is suspected, immediately discontinue haloperidol decanoate and provide intensive symptomatic treatment and monitoring.

5.7 Neurological Adverse Reactions in Patients with Parkinson’s Disease or Dementia with Lewy Bodies Patients with Parkinson’s disease or Dementia with Lewy bodies may experience increased sensitivity to haloperidol. Manifestations of this increased sensitivity include severe extrapyramidal symptoms (e.g., tremor, rigidity, bradykinesia), confusion, sedation, and falls. Haloperidol decanoate is contraindicated in patients with Dementia with Lewy bodies and in patients with Parkinson’s disease.

5.8 Seizures Haloperidol decanoate may lower the seizure threshold. Haloperidol decanoate is generally not recommended in patients receiving antiseizure drugs or have a history of seizures or EEG abnormalities. If clinically indicated, maintain patients taking haloperidol decanoate on adequate antiseizure therapy.

5.9 Hypersensitivity Reactions There have been postmarketing reports of hypersensitivity reactions with haloperidol including anaphylactic reaction, angioedema, dermatitis exfoliative, hypersensitivity vasculitis, rash, urticaria, face edema, laryngeal edema, bronchospasm, and laryngospasm <span class="opacity-50 text-xs">[see Adverse Reactions ( 6.2 )]</span>. Haloperidol decanoate injection is contraindicated in patients with known hypersensitivity to haloperidol or any components of haloperidol decanoate injection.

5.10 Falls Antipsychotics, including haloperidol decanoate, may cause somnolence, orthostatic hypotension, motor instability and sensory abnormality, which may lead to falls and, consequently, fractures and other injuries. If patients have a condition (or take concomitant drugs) that could exacerbate these effects, complete fall risk assessments when initiating haloperidol decanoate treatment and periodically during long-term treatment.

5.11 Potential for Cognitive and Motor Impairment Haloperidol decanoate may impair judgement, thinking, or motor skills. Inform patients of the risk and advise them to not drive a motor vehicle or operate hazardous machinery until they are reasonably certain that treatment with haloperidol decanoate does not impair their cognitive and motor functions.

5.12 Risk of Encephalopathic Syndrome with Concomitant Use of Lithium An encephalopathic syndrome, characterized by weakness, lethargy, fever, tremulousness, confusion, extrapyramidal symptoms, leukocytosis, and elevated serum enzymes (AST, ALT, GGT, alkaline phosphatase, CK, and LDH), BUN, and fasting blood sugar, followed by irreversible brain damage has occurred in a few patients treated with concomitant haloperidol and lithium. Monitor patients who concomitantly use haloperidol decanoate and lithium closely for early signs of neurological toxicity, and discontinue haloperidol decanoate or both haloperidol decanoate and lithium promptly if such signs appear.

5.13 Leukopenia, Neutropenia, and Agranulocytosis Leukopenia, neutropenia and agranulocytosis (including fatal cases) have been reported during treatment with antipsychotic drugs, including haloperidol decanoate <span class="opacity-50 text-xs">[see Adverse Reactions ( 6.2 )]</span>. Possible risk factors for antipsychotic drug-associated leukopenia and neutropenia include pre-existing low WBC and history of drug-induced leukopenia and neutropenia. Perform frequent complete blood count (CBC) monitoring during the first few months of haloperidol decanoate therapy in patients with a history of a clinically significant low WBC, drug-induced leukopenia or neutropenia. Consider discontinuing haloperidol decanoate in patients who have a clinically significant decline in their WBC in the absence of other causative factors. Discontinue haloperidol decanoate in patients with clinically significant neutropenia or an absolute neutrophil count of &lt;1,000/mm 3 and monitor closely until the neutropenia resolves.

5.14 Hyperprolactinemia Antipsychotic drugs elevate prolactin levels during acute and chronic use and may result in galactorrhea, amenorrhea, gynecomastia, and impotence which have been reported with antipsychotic drugs <span class="opacity-50 text-xs">[see Adverse Reactions ( 6.1 , 6.2 ) and Use in Specific Populations ( 8.3 )]</span>. Published epidemiologic studies have shown inconsistent results regarding the potential association between hyperprolactinemia and breast cancer <span class="opacity-50 text-xs">[see Nonclinical Toxicology ( 13.1 )]</span>.

5.15 Risk of Severe Neurotoxicity in Patients with Thyrotoxicosis Severe neurotoxicity (rigidity, inability to walk or talk) may occur in patients with thyrotoxicosis who are also receiving antipsychotic drugs, including haloperidol decanoate.