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Clinical Worsening And Adverse Effects
Huntington's disease is a progressive disorder characterized by changes in mood, cognition, chorea, rigidity, and functional capacity over time. In a 12-week controlled trial, XENAZINE was also shown to cause slight worsening in mood, cognition, rigidity, and functional capacity. Whether these effects persist, resolve, or worsen with continued treatment is unknown.
Prescribers should periodically re-evaluate the need for XENAZINE in their patients by assessing the beneficial effect on chorea and possible adverse effects, including depression, cognitive decline, parkinsonism, dysphagia, sedation/somnolence, akathisia, restlessness and disability. It may be difficult to distinguish between drug-induced side-effects and progression of the underlying disease; decreasing the dose or stopping the drug may help the clinician distinguish between the two possibilities. In some patients, underlying chorea itself may improve over time, decreasing the need for XENAZINE.
Depression And Suicidality
Patients with Huntington's disease are at increased risk for depression, suicidal ideation or behaviors (suicidality). XENAZINE increases the risk for suicidality in patients with HD. All patients treated with XENAZINE should be observed for new or worsening depression or suicidality. If depression or suicidality does not resolve, consider discontinuing treatment with XENAZINE.
In a 12-week, double-blind placebo-controlled study in patients with chorea associated with Huntington's disease, 10 of 54 patients (19%) treated with XENAZINE were reported to have an adverse event of depression or worsening depression compared to none of the 30 placebo-treated patients. In two open-label studies (in one study, 29 patients received XENAZINE for up to 48 weeks; in the second study, 75 patients received XENAZINE for up to 80 weeks), the rate of depression/worsening depression was 35%.
In all of the HD chorea studies of XENAZINE (n=187), one patient committed suicide, one attempted suicide, and six had suicidal ideation.
Clinicians should be alert to the heightened risk of suicide in patients with Huntington's disease regardless of depression indices. Reported rates of completed suicide among individuals with Huntington's disease ranged from 3-13% and over 25% of patients attempt suicide at some point in their illness.
Patients, their caregivers, and families should be informed of the risks of depression, worsening depression, and suicidality associated with XENAZINE and should be instructed to report behaviors of concern promptly to the treating physician. Patients with HD who express suicidal ideation should be evaluated immediately.
Before prescribing a daily dose of XENAZINE that is greater than 50 mg per day, patients should be genotyped to determine if they express the drug metabolizing enzyme, CYP2D6. CYP2D6 testing is necessary to determine whether patients are poor metabolizers (PMs), extensive (EMs) or intermediate metabolizers (IMs) of XENAZINE.
Patients who are PMs of XENAZINE will have substantially higher levels of the primary drug metabolites (about 3-fold for α-HTBZ and 9-fold for β-HTBZ) than patients who are EMs. The dosage should be adjusted according to a patient's CYP2D6 metabolizer status. In patients who are identified as CYP2D6 PMs, the maximum recommended total daily dose is 50 mg and the maximum recommended single dose is 25 mg [see DOSAGE AND ADMINISTRATION, Use In Specific Populations, CLINICAL PHARMACOLOGY].
Neuroleptic Malignant Syndrome (NMS)
A potentially fatal symptom complex sometimes referred to as Neuroleptic Malignant Syndrome (NMS) has been reported in association with XENAZINE and other drugs that reduce dopaminergic transmission [see Tardive Dyskinesia, DRUG INTERACTIONS]. Clinical manifestations of NMS are hyperpyrexia, muscle rigidity, altered mental status, and evidence of autonomic instability (irregular pulse or blood pressure, tachycardia, diaphoresis, and cardiac dysrhythmia). Additional signs may include elevated creatinine phosphokinase, myoglobinuria, rhabdomyolysis, and acute renal failure. The diagnosis of NMS can be complicated; other serious medical illness (e.g., pneumonia, systemic infection), and untreated or inadequately treated extrapyramidal disorders can present with similar signs and symptoms. Other important considerations in the differential diagnosis include central anticholinergic toxicity, heat stroke, drug fever, and primary central nervous system pathology.
The management of NMS should include (1) immediate discontinuation of XENAZINE and other drugs not essential to concurrent therapy; (2) intensive symptomatic treatment and medical monitoring; and (3) treatment of any concomitant serious medical problems for which specific treatments are available. There is no general agreement about specific pharmacological treatment regimens for NMS.
Recurrence of NMS has been reported. If treatment with XENAZINE is needed after recovery from NMS, patients should be monitored for signs of recurrence.
Akathisia, Restlessness, And Agitation
In a 12-week, double-blind, placebo-controlled study in patients with chorea associated with HD, akathisia was observed in 10 (19%) of XENAZINE-treated patients and 0% of placebo-treated patients. In an 80-week open-label study, akathisia was observed in 20% of XENAZINE-treated patients. Akathisia was not observed in a 48week open-label study. Patients receiving XENAZINE should be monitored for the presence of akathisia. Patients receiving XENAZINE should also be monitored for signs and symptoms of restlessness and agitation, as these may be indicators of developing akathisia. If a patient develops akathisia, the XENAZINE dose should be reduced; however, some patients may require discontinuation of therapy.
XENAZINE can cause parkinsonism. In a 12-week double-blind, placebo-controlled study in patients with chorea associated with HD, symptoms suggestive of parkinsonism (i.e., bradykinesia, hypertonia and rigidity) were observed in 15% of XENAZINE-treated patients compared to 0% of placebo-treated patients. In 48-week and 80-week open-label studies, symptoms suggestive of parkinsonism were observed in 10% and 3% of XENAZINE-treated patients, respectively. Because rigidity can develop as part of the underlying disease process in Huntington's disease, it may be difficult to distinguish between this drug-induced side-effect and progression of the underlying disease process. Drug-induced parkinsonism has the potential to cause more functional disability than untreated chorea for some patients with Huntington's disease. If a patient develops parkinsonism during treatment with XENAZINE, dose reduction should be considered; in some patients, discontinuation of therapy may be necessary.
Dysphagia is a component of HD. However, drugs that reduce dopaminergic transmission have been associated with esophageal dysmotility and dysphagia. Dysphagia may be associated with aspiration pneumonia. In a 12week, double-blind, placebo-controlled study in patients with chorea associated with HD, dysphagia was observed in 4% of XENAZINE-treated patients and 3% of placebo-treated patients. In 48-week and 80-week open-label studies, dysphagia was observed in 10% and 8% of XENAZINE-treated patients, respectively. Some of the cases of dysphagia were associated with aspiration pneumonia. Whether these events were related to treatment is unknown.
Sedation And Somnolence
Sedation is the most common dose-limiting adverse reaction of XENAZINE. In a 12-week, double-blind, placebo-controlled trial in patients with chorea associated with HD, sedation/somnolence occurred in 17/54 (31%) XENAZINE-treated patients and in 1 (3%) placebo-treated patient. Sedation was the reason upward titration of XENAZINE was stopped and/or the dose of XENAZINE was decreased in 15/54 (28%) patients. In all but one case, decreasing the dose of XENAZINE resulted in decreased sedation. In 48-week and 80-week open-label studies, sedation/somnolence occurred in 17% and 57% of XENAZINE treated patients, respectively. In some patients, sedation occurred at doses that were lower than recommended doses.
Patients should not perform activities requiring mental alertness to maintain the safety of themselves or others, such as operating a motor vehicle or operating hazardous machinery, until they are on a maintenance dose of XENAZINE and know how the drug affects them.
XENAZINE causes a small increase (about 8 msec) in the corrected QT (QTc) interval. QT prolongation can lead to development of torsade de pointes-type ventricular tachycardia with the risk increasing as the degree of prolongation increases [see CLINICAL PHARMACOLOGY]. The use of XENAZINE should be avoided in combination with other drugs that are known to prolong QTc, including antipsychotic medications (e.g., chlorpromazine, haloperidol, thioridazine, ziprasidone), antibiotics (e.g., moxifloxacin), Class 1A (e.g., quinidine, procainamide), and Class III (e.g., amiodarone, sotalol) antiarrhythmic medications or any other medications known to prolong the QTc interval [see DRUG INTERACTIONS].
XENAZINE should also be avoided in patients with congenital long QT syndrome and in patients with a history of cardiac arrhythmias. Certain circumstances may increase the risk of the occurrence of torsade de pointes and/or sudden death in association with the use of drugs that prolong the QTc interval, including (1) bradycardia; (2) hypokalemia or hypomagnesemia; (3) concomitant use of other drugs that prolong the QTc interval; and (4) presence of congenital prolongation of the QT interval [see CLINICAL PHARMACOLOGY].
Hypotension And Orthostatic Hypotension
XENAZINE induced postural dizziness in healthy volunteers receiving single doses of 25 or 50 mg. One subject had syncope and one subject with postural dizziness had documented orthostasis. Dizziness occurred in 4% of XENAZINE-treated patients (vs. none on placebo) in the 12-week controlled trial; however, blood pressure was not measured during these events. Monitoring of vital signs on standing should be considered in patients who are vulnerable to hypotension.
XENAZINE elevates serum prolactin concentrations in humans. Following administration of 25 mg to healthy volunteers, peak plasma prolactin levels increased 4-to 5-fold. Tissue culture experiments indicate that approximately one third of human breast cancers are prolactin-dependent in vitro, a factor of potential importance if XENAZINE is being considered for a patient with previously detected breast cancer. Although amenorrhea, galactorrhea, gynecomastia and impotence can be caused by elevated serum prolactin concentrations, the clinical significance of elevated serum prolactin concentrations for most patients is unknown. Chronic increase in serum prolactin levels (although not evaluated in the XENAZINE development program) has been associated with low levels of estrogen and increased risk of osteoporosis. If there is a clinical suspicion of symptomatic hyperprolactinemia, appropriate laboratory testing should be done and consideration should be given to discontinuation of XENAZINE.
Tardive Dyskinesia (TD)
A potentially irreversible syndrome of involuntary, dyskinetic movements may develop in patients treated with neuroleptic drugs. In an animal model of orofacial dyskinesias, acute administration of reserpine, a monoamine depletor, has been shown to produce vacuous chewing in rats. Although the pathophysiology of tardive dyskinesia remains incompletely understood, the most commonly accepted hypothesis of the mechanism is that prolonged post-synaptic dopamine receptor blockade leads to supersensitivity to dopamine. Neither reserpine nor XENAZINE, which are dopamine depletors, have been reported to cause clear tardive dyskinesia in humans, but as pre-synaptic dopamine depletion could theoretically lead to supersensitivity to dopamine, and XENAZINE can cause the extrapyramidal symptoms also known to be associated with neuroleptics (e.g., parkinsonism and akathisia), physicians should be aware of the possible risk of tardive dyskinesia. If signs and symptoms of TD appear in a patient treated with XENAZINE, drug discontinuation should be considered.
Binding To Melanin-Containing Tissues
Since XENAZINE or its metabolites bind to melanin-containing tissues, it could accumulate in these tissues over time. This raises the possibility that XENAZINE may cause toxicity in these tissues after extended use. Neither ophthalmologic nor microscopic examination of the eye was conducted in the chronic toxicity study in dogs. Ophthalmologic monitoring in humans was inadequate to exclude the possibility of injury occurring after long-term exposure.
The clinical relevance of XENAZINE's binding to melanin-containing tissues is unknown. Although there are no specific recommendations for periodic ophthalmologic monitoring, prescribers should be aware of the possibility of long-term ophthalmologic effects [see CLINICAL PHARMACOLOGY].
Patient Counseling Information
Advise the patient to read the FDA-approved patient labeling (Medication Guide).
Risk of Suicidality
Inform patients and their families that XENAZINE may increase the risk of suicidal thinking and behaviors. Counsel patients and their families to remain alert to the emergence of suicidal ideation and to report it immediately to the patient's physician [see CONTRAINDICATIONS, WARNINGS AND PRECAUTIONS].
Risk of Depression
Inform patients and their families that XENAZINE may cause depression or may worsen pre-existing depression. Encourage patients and their families to be alert to the emergence of sadness, worsening of depression, withdrawal, insomnia, irritability, hostility (aggressiveness), akathisia (psychomotor restlessness), anxiety, agitation, or panic attacks and to report such symptoms promptly to the patient's physician [see CONTRAINDICATIONS, WARNINGS AND PRECAUTIONS].
Dosing of XENAZINE
Inform patients and their families that the dose of XENAZINE will be increased slowly to the dose that is best for each patient. Sedation, akathisia, parkinsonism, depression, and difficulty swallowing may occur. Such symptoms should be promptly reported to the physician and the XENAZINE may dose need to be reduced or discontinued [see DOSAGE AND ADMINISTRATION].
Risk of Sedation and Somnolence
Inform patients that XENAZINE may induce sedation and somnolence and may impair the ability to perform tasks that require complex motor and mental skills. Advise patients that until they learn how they respond to XENAZINE, they should be careful doing activities that require them to be alert, such as driving a car or operating machinery [see WARNINGS AND PRECAUTIONS].
Interaction with Alcohol
Advise patients and their families that alcohol may potentiate the sedation induced by XENAZINE [see DRUG INTERACTIONS].
Usage in Pregnancy
Advise patients and their families to notify the physician if the patient becomes pregnant or intends to become pregnant during XENAZINE therapy, or is breast-feeding or intending to breast-feed an infant during therapy [see Use In Specific Populations].
Carcinogenesis, Mutagenesis, Impairment Of Fertility
No increase in tumors was observed in p53+/– transgenic mice treated orally with tetrabenazine at doses of 0, 5, 15 and 30 mg/kg/day for 26 weeks. When compared to humans receiving a 50 mg dose of XENAZINE, mice dosed with a 30 mg/kg dose of tetrabenazine produce about one sixth the levels of 9-desmethyl-beta-DHTBZ, a major human metabolite. Therefore, this study may not have adequately characterized the potential of tetrabenazine to be carcinogenic in people.
Tetrabenazine and metabolites α-HTBZ and β-HTBZ were negative in the in vitro bacterial reverse mutation assay. Tetrabenazine was clastogenic in the in vitro chromosome aberration assay in Chinese hamster ovary cells in the presence of metabolic activation. α-HTBZ and β-HTBZ were clastogenic in the in vitro chromosome aberration assay in Chinese hamster lung cells in the presence and absence of metabolic activation. In vivo micronucleus tests were conducted in male and female rats and male mice. Tetrabenazine was negative in male mice and rats but produced an equivocal response in female rats.
Because the bioactivation system used in the in vitro studies was hepatic S9 fraction prepared from rat, a species that, when dosed with tetrabenazine, does not produce 9-desmethyl-beta-DHTBZ, a major human metabolite, these studies may not have adequately assessed the potential of XENAZINE to be mutagenic in humans. Furthermore, since the mouse produces very low levels of this metabolite when dosed with tetrabenazine, the in vivo study may not have adequately assessed the potential of XENAZINE to be mutagenic in humans.
Impairment of Fertility
Oral administration of tetrabenazine (doses of 5, 15, or 30 mg/kg/day) to female rats prior to and throughout mating, and continuing through day 7 of gestation resulted in disrupted estrous cyclicity at doses greater than 5 mg /kg/day (less than the MRHD on a mg/m² basis).
No effects on mating and fertility indices or sperm parameters (motility, count, density) were observed when males were treated orally with tetrabenazine (doses or 5, 15 or 30 mg/kg/day; up to 3 times the MRHD on a mg/m² basis) prior to and throughout mating with untreated females.
Because rats dosed with tetrabenazine do not produce 9-desmethyl-beta-DHTBZ, a major human metabolite, these studies may not have adequately assessed the potential of XENAZINE to impair fertility in humans.
Use In Specific Populations
Pregnancy Category C
There are no adequate and well-controlled studies in pregnant women. XENAZINE should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
Tetrabenazine had no clear effects on embryo-fetal development when administered to pregnant rats throughout the period of organogenesis at oral doses up to 30 mg/kg/day (or 3 times the maximum recommended human dose [MRHD] of 100 mg/day on a mg/m² basis). Tetrabenazine had no effects on embryo-fetal development when administered to pregnant rabbits during the period of organogenesis at oral doses up to 60 mg/kg/day (or 12 times the MRHD on a mg/m² basis). Because neither rat nor rabbit dosed with tetrabenazine produce 9desmethyl-beta-DHTBZ, a major human metabolite, these studies may not have adequately addressed the potential effects of tetrabenazine on embryo-fetal development in humans.
When tetrabenazine was administered to female rats (doses of 5, 15, and 30 mg/kg/day) from the beginning of organogenesis through the lactation period, an increase in stillbirths and offspring postnatal mortality was observed at 15 and 30 mg/kg/day and delayed pup maturation was observed at all doses. The no-effect dose for stillbirths and postnatal mortality was 0.5 times the MRHD on a mg/m² basis. Because rats dosed with tetrabenazine do not produce 9-desmethyl-beta-DHTBZ, a major human metabolite, this study may not have adequately assessed the potential effects of tetrabenazine on the offspring of women exposed in utero and via lactation.
Labor And Delivery
The effect of XENAZINE on labor and delivery in humans is unknown.
It is not known whether XENAZINE or its metabolites are excreted in human milk.
Since many drugs are excreted into human milk and because of the potential for serious adverse reactions in nursing infants from XENAZINE, a decision should be made whether to discontinue nursing or to discontinue XENAZINE, taking into account the importance of the drug to the mother.
The safety and efficacy of XENAZINE in pediatric patients have not been established.
The pharmacokinetics of XENAZINE and its primary metabolites have not been formally studied in geriatric subjects.
Because the safety and efficacy of the increased exposure to XENAZINE and other circulating metabolites are unknown, it is not possible to adjust the dosage of XENAZINE in hepatic impairment to ensure safe use. The use of XENAZINE in patients with hepatic impairment is contraindicated [see CONTRAINDICATIONS, CLINICAL PHARMACOLOGY].
Poor Or Extensive CYP2D6 Metabolizers
Patients who require doses of XENAZINE greater than 50 mg per day, should be first tested and genotyped to determine if they are poor (PMs) or extensive metabolizers (EMs) by their ability to express the drug metabolizing enzyme, CYP2D6. The dose of XENAZINE should then be individualized accordingly to their status as either poor (PMs) or extensive metabolizers (EMs) [see DOSAGE AND ADMINISTRATION, WARNINGS AND PRECAUTIONS, CLINICAL PHARMACOLOGY].
Poor CYP2D6 metabolizers (PM) will have substantially higher levels of exposure to the primary metabolites (about 3-fold for α-HTBZ and 9-fold for β-HTBZ) compared to EMs. The dosage should, therefore, be adjusted according to a patient's CYP2D6 metabolizer status by limiting a single dose to a maximum of 25 mg and the recommended daily dose to not exceed a maximum of 50 mg/day in patients who are CYP2D6 PMs [see DOSAGE AND ADMINISTRATION, WARNINGS AND PRECAUTIONS, CLINICAL PHARMACOLOGY].
Extensive / Intermediate Metabolizers
In extensive (EMs) or intermediate metabolizers (IMs), the dosage of XENAZINE can be titrated to a maximum single dose of 37.5 mg and a recommended maximum daily dose of 100 mg [see DOSAGE AND ADMINISTRATION, DRUG INTERACTIONS, CLINICAL PHARMACOLOGY].This monograph has been modified to include the generic and brand name in many instances.
Last reviewed on RxList: 6/19/2015
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