"The US Food and Drug Administration (FDA) has approved another atypical antipsychotic for the treatment of pediatric patients with bipolar I disorder.
According to a release issued by the drug's manufacturer, Actavis, asenapine (Sa"...
Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect or predict the rates observed in practice.
Clinical Trials Experience
Adverse reactions were recorded by clinical investigators using descriptive terminology of their own choosing. Consequently, it is not possible to provide a meaningful estimate of the proportion of individuals experiencing adverse reactions without first grouping similar types of reactions into a limited (i.e., reduced) number of standardized reaction categories.
In the tables and tabulations that follow, MedDRA or COSTART Dictionary terminology has been used to classify reported adverse reactions. The data in the tables represent the proportion of individuals who experienced, at least once, a treatment-emergent adverse reaction of the type listed. A reaction was considered treatment-emergent if it occurred for the first time or worsened while receiving therapy following baseline evaluation. It is possible that reactions reported during therapy were not necessarily related to drug exposure.
The prescriber should be aware that the figures in the tables and tabulations cannot be used to predict the incidence of side effects in the course of usual medical practice where patient characteristics and other factors differ from those that prevailed in the clinical studies. Similarly, the cited frequencies cannot be compared with figures obtained from other clinical investigations involving different treatments, uses, and investigators. The cited figures, however, do provide the prescribing clinician with some basis for estimating the relative contribution of drug and nondrug factors to the side effect incidence rate in the population studied.
The information below is derived from a clinical study database for SYMBYAX consisting of 2547 patients with treatment resistant depression, depressive episodes associated with Bipolar I Disorder, Major Depressive Disorder with psychosis, or sexual dysfunction with approximately 1085 patient-years of exposure. The conditions and duration of treatment with SYMBYAX varied greatly and included (in overlapping categories) open-label and double-blind phases of studies, inpatients and outpatients, fixed-dose and dose-titration studies, and short-term or long-term exposure.
Adverse Reactions Associated with Discontinuation of Treatment in Short-Term, Controlled Studies Including Depressive Episodes Associated with Bipolar I Disorder and Treatment Resistant Depression
Overall, 11.3% of the 771 patients in the SYMBYAX group discontinued due to adverse reactions compared with 4.4% of the 477 patients for placebo. Adverse reactions leading to discontinuation associated with the use of SYMBYAX (incidence of at least 1% for SYMBYAX and greater than that for placebo) using MedDRA Dictionary coding were weight increased (2%) and sedation (1%) versus placebo patients which had 0% incidence of weight increased and sedation.
Commonly Observed Adverse Reactions in Short-Term, Controlled Studies Including Depressive Episodes Associated with Bipolar I Disorder and Treatment Resistant Depression
The most commonly observed adverse reactions associated with the use of SYMBYAX (incidence ≥ 5% and at least twice that for placebo in the SYMBYAX-controlled database) using MedDRA Dictionary coding were: disturbance in attention, dry mouth, fatigue, hypersomnia, increased appetite, peripheral edema, sedation, somnolence, tremor, vision blurred, and weight increased. Adverse reactions reported in clinical trials of olanzapine and fluoxetine in combination are generally consistent with treatment-emergent adverse reactions during olanzapine or fluoxetine monotherapy.
Adverse Reactions Occurring at an Incidence of 2% or More in Short-Term Controlled Studies Including Depressive Episodes Associated with Bipolar I Disorder and Treatment Resistant Depression
Table 13 enumerates the treatment-emergent adverse reactions associated with the use of SYMBYAX (incidence of at least 2% for SYMBYAX and twice or more than for placebo). The SYMBYAX-controlled column includes patients with various diagnoses while the placebo column includes only patients with bipolar depression and major depression with psychotic features.
Table 13: Treatment-Emergent Adverse Reactions:
Incidence in the Adult Controlled Clinical Studies
|System Organ Class||Adverse Reaction||Percentage of Patients Reporting Event|
|Eye disorders||Vision blurred||5||2|
|Gastrointestinal disorders||Dry mouth||15||6|
|General disorders and administration site conditions||Fatigue||12||2|
|Infections and infestations||Sinusitis||2||1|
|Metabolism and nutrition disorders||Increased appetite||20||4|
|Musculoskeletal and connective tissue disorders||Arthralgia||4||1|
|Pain in extremity||3||1|
|Nervous system disorders||Somnolenceb||27||11|
|Disturbance in attention||5||1|
|Reproductive system and breast disorders||Erectile dysfunction||2||1|
|a Includes edema, edema peripheral, pitting
edema, generalized edema, eyelid edema, face edema, gravitational edema,
localized edema, periorbital edema, swelling, joint swelling, swelling face,
and eye swelling.
b Includes somnolence, sedation, hypersomnia, and lethargy.
Dystonia, Class Effect for Antipsychotics — Symptoms of dystonia, prolonged abnormal contractions of muscle groups, may occur in susceptible individuals during the first few days of treatment. Dystonic symptoms include: spasm of the neck muscles, sometimes progressing to tightness of the throat, swallowing difficulty, difficulty breathing, and/or protrusion of the tongue. While these symptoms can occur at low doses, the frequency and severity are greater with high potency and at higher doses of first generation antipsychotic drugs. In general, an elevated risk of acute dystonia may be observed in males and younger age groups receiving antipsychotics; however, events of dystonia have been reported infrequently ( < 1%) with the olanzapine and fluoxetine combination.
Additional Findings Observed in Clinical Studies
Sexual Dysfunction — In the pool of controlled SYMBYAX studies in patients with bipolar depression, there were higher rates of the treatment-emergent adverse reactions decreased libido, anorgasmia, erectile dysfunction and abnormal ejaculation in the SYMBYAX group than in the placebo group. One case of decreased libido led to discontinuation in the SYMBYAX group. In the controlled studies that contained a fluoxetine arm, the rates of decreased libido and abnormal ejaculation in the SYMBYAX group were less than the rates in the fluoxetine group. None of the differences were statistically significant.
Sexual dysfunction, including priapism, has been reported with all SSRIs. While it is difficult to know the precise risk of sexual dysfunction associated with the use of SSRIs, physicians should routinely inquire about such possible side effects.
There are no adequate and well-controlled studies examining sexual dysfunction with SYMBYAX or fluoxetine treatment. Symptoms of sexual dysfunction occasionally persist after discontinuation of fluoxetine treatment.
Difference Among Dose Levels Observed in Other Olanzapine Clinical Trials
In a single 8-week randomized, double-blind, fixed-dose study comparing 10 (N=199), 20 (N=200), and 40 (N=200) mg/day of olanzapine in patients with schizophrenia or schizoaffective disorder, statistically significant differences among 3 dose groups were observed for the following safety outcomes: weight gain, prolactin elevation, fatigue, and dizziness. Mean baseline to endpoint increase in weight (10 mg/day: 1.9 kg; 20 mg/day: 2.3 kg; 40 mg/day: 3 kg) was observed with significant differences between 10 vs 40 mg/day. Incidence of treatment-emergent prolactin elevation > 24.2 ng/mL (female) or > 18.77 ng/mL (male) at any time during the trial (10 mg/day: 31.2%; 20 mg/day: 42.7%; 40 mg/day: 61.1%) with significant differences between 10 vs 40 mg/day and 20 vs 40 mg/day; fatigue (10 mg/day: 1.5%; 20 mg/day: 2.1%; 40 mg/day: 6.6%) with significant differences between 10 vs 40 and 20 vs 40 mg/day; and dizziness (10 mg/day: 2.6%; 20 mg/day: 1.6%; 40 mg/day: 6.6%) with significant differences between 20 vs 40 mg, was observed.
Other Adverse Reactions Observed in Clinical Studies
Following is a list of treatment-emergent adverse reactions reported by patients treated with SYMBYAX in clinical trials. This listing is not intended to include reactions (1) already listed in previous tables or elsewhere in labeling, (2) for which a drug cause was remote, (3) which were so general as to be uninformative, (4) which were not considered to have significant clinical implications, or (5) which occurred at a rate equal to or less than placebo.
Reactions are classified by body system using the following definitions: frequent adverse reactions are those occurring in at least 1/100 patients; infrequent adverse reactions are those occurring in 1/100 to 1/1000 patients; and rare reactions are those occurring in fewer than 1/1000 patients.
Body as a Whole — Frequent: chills, neck rigidity, photosensitivity reaction; Rare: death1.
Cardiovascular System — Frequent: vasodilatation; Infrequent: QT-interval prolonged.
Digestive System — Frequent: diarrhea; Infrequent: gastritis, gastroenteritis, nausea and vomiting, peptic ulcer; Rare: gastrointestinal hemorrhage, intestinal obstruction, liver fatty deposit, pancreatitis.
Metabolic and Nutritional — Frequent: generalized edema, weight loss; Rare: bilirubinemia, creatinine increased, gout.
Musculoskeletal System — Rare: osteoporosis.
Nervous System — Frequent: amnesia; Infrequent: ataxia, buccoglossal syndrome, coma, depersonalization, dysarthria, emotional lability, euphoria, hypokinesia, movement disorder, myoclonus; Rare: hyperkinesia, libido increased, withdrawal syndrome.
Special Senses — Frequent: taste perversion; Infrequent: abnormality of accommodation, dry eyes.
Urogenital System — Frequent: breast pain, menorrhagia2, urinary frequency, urinary incontinence; Infrequent: amenorrhea2, female lactation2, hypomenorrhea2, metrorrhagia2, urinary retention, urinary urgency, urination impaired; Rare: breast engorgement2.
Other Adverse Reactions Observed with Olanzapine or Fluoxetine Monotherapy
The following adverse reactions were not observed in SYMBYAX-treated patients during premarketing clinical studies but have been reported with olanzapine or fluoxetine monotherapy: aplastic anemia, bruxism, cholestatic jaundice, diabetic coma, dysuria, eosinophilic pneumonia3, erythema multiforme, esophageal ulcer, gynecological bleeding, headache, hypotension, jaundice, neutropenia, sudden unexpected death3, sweating, and violent behaviors3. Random triglyceride levels of ≥ 1000 mg/dL have been reported.
Children and Adolescent Patients (aged 10 to 17 years) with a Diagnosis of Bipolar Depression
The information below is derived from a single, 8-week, randomized, placebo-controlled clinical trial investigating SYMBYAX for the treatment of bipolar I depression in patients 10 to 17 years of age.
Adverse Reactions Associated with Discontinuation of Treatment in the single pediatric study
Overall, 14.1% of the 170 patients in the SYMBYAX group discontinued due to adverse reactions compared with 5.9% of the 85 patients for placebo. Adverse reactions leading to discontinuation associated with the use of SYMBYAX (incidence of at least 1% for SYMBYAX and greater than that for placebo) using MedDRA Dictionary coding were weight increased (2.9%), suicidal ideation (1.8%), bipolar disorder (1.2%), and somnolence (1.2%) versus placebo patients which had 0% incidence of weight increased, bipolar disorder, and somnolence, and a 1.2% incidence of suicidal ideation.
Adverse Reactions Occurring at an Incidence of 2% or more and greater than placebo — Table 14 enumerates the treatment-emergent adverse reactions associated with the use of SYMBYAX (incidence of at least 2% for SYMBYAX and twice or more than for placebo).
Table 14: Treatment-Emergent Adverse Reactions:
Incidence in a 8-week randomized, double-blind, placebo-controlled clinical
trial in pediatric bipolar I depression.
|System Organ Class||Adverse Reaction||Percentage of Patients Reporting Event|
|Nervous system disorders||Somnolencea||24||2|
|Blood triglycerides increased||7||2|
|Blood cholesterol increased||4||0|
|Hepatic enzyme increasedb||9||1|
|Metabolism and nutrition disorders||Increased appetite||17||1|
|Musculoskeletal and connective tissue disorders||Back pain||2||1|
|Injury, poisoning and procedural complications||Accidental overdose||3||1|
|Reproductive system and breast disorders||Dysmenorrhea||2||0|
|aIncludes somnolence, sedation, and hypersomnia. No lethargy
bIncludes alanine aminotransferase increased, aspartate aminotransferase increased, hepatic enzyme increased, liver function test abnormal, gamma-glutamyltransferase increased, and transaminases increased.
Vital Signs and Laboratory Studies
Vital Signs — Tachycardia, bradycardia, and orthostatic hypotension have occurred in SYMBYAX-treated patients [see WARNINGS AND PRECAUTIONS]. The mean standing pulse rate of SYMBYAX-treated patients was reduced by 0.7 beats/min.
Laboratory Changes — In SYMBYAX clinical studies (including treatment resistant depression, depressive episodes associated with Bipolar I Disorder, Major Depressive Disorder with psychosis, or sexual dysfunction), SYMBYAX was associated with statistically significantly greater frequencies for the following treatment-emergent findings in laboratory analytes (normal at baseline to abnormal at any time during the trial) compared to placebo: elevated prolactin (28% vs 5%); elevated urea nitrogen (3% vs 0.8%); elevated uric acid (3% vs 0.5%); low albumin (3% vs 0.3%); low bicarbonate (14% vs 9%); low hemoglobin (3% vs 0%); low inorganic phosphorus (2% vs 0.3%); low lymphocytes (2% vs 0%); and low total bilirubin (15% vs 4%).
As with olanzapine, asymptomatic elevations of hepatic aminotransferases [ALT, AST, and GGT] and alkaline phosphatase have been observed with SYMBYAX. In the SYMBYAX-controlled database, clinically significant ALT elevations (change from < 3 times the upper limit of normal [ULN] at baseline to ≥ 3 times ULN) were observed in 5% (38/698) of patients exposed to SYMBYAX compared with 0.5% (2/378) of placebo-treated patients and 4% (33/751) of olanzapine-treated patients. ALT elevations ≥ 5 times ULN were observed in 2% (11/701) of SYMBYAX-treated patients, compared to 0.3% (1/379) of placebo-treated patients and 1% (11/760) of olanzapine-treated patients. No patient with elevated ALT values experienced jaundice or liver failure, or met the criteria for Hy's Rule. ALT values returned to normal, or were decreasing, at last follow-up in the majority of patients who either continued treatment with SYMBYAX or discontinued SYMBYAX.
Rare postmarketing reports of hepatitis have been received in patients treated with olanzapine. Very rare cases of cholestatic or mixed liver injury have also been reported in the postmarketing period in patients treated with olanzapine.
Caution should be exercised in patients with signs and symptoms of hepatic impairment, in patients with preexisting conditions associated with limited hepatic functional reserve, and in patients who are being treated with potentially hepatotoxic drugs.
An increase in creatine phosphokinase has been reported very rarely in SYMBYAX-treated patients and infrequently in clinical trials of olanzapine-treated patients.
QT Interval Prolongation — The mean increase in QTc interval for SYMBYAX-treated patients (4.4 msec) in clinical studies was significantly greater than that for placebo-treated (-0.8 msec), olanzapine-treated (-0.3 msec) patients, and fluoxetine-treated (1.7 msec) patients. There were no significant differences between patients treated with SYMBYAX, placebo, olanzapine, or fluoxetine in the incidence of QTc outliers ( > 500 msec).
Children and Adolescents (aged 10 -17 years)
In a single 8-week randomized, placebo-controlled clinical trial investigating SYMBYAX for treatment of bipolar I depression in patients 10 to 17 years of age, the following was observed:
Vital Signs — In the SYMBYAX-treated patients compared with placebo-treated patients, the mean orthostatic blood pressure and standing pulse rate were not significantly different between treatment groups.
Body Weight: An increase in weight greater than or equal to 7% occurred in 52.4% of the SYMBYAX group and 3.6% of the placebo group. Weight gain greater than or equal to 15% occurred in 14.1% of the SYMBYAX group and none of the placebo group.
Laboratory Changes — SYMBYAX was associated with statistically significantly greater frequencies for the following treatment-emergent findings in laboratory analytes (normal or low at baseline to abnormal at any time during the trial) compared to placebo: elevated ALT (45.9% vs 2.5%); elevated AST (33.7% vs 7.6%); high fasting total cholesterol (28.9% vs 8.2%); high fasting LDL cholesterol (19.7% vs 6.5%); high fasting triglycerides (52.3% vs 27.3%), and elevated prolactin (85% vs 36%). No patient with elevated hepatic enzyme values experienced jaundice or liver failure, or met the criteria for Hy's Rule. Five patients experienced an adverse event potentially associated with elevated prolactin; these events included dysmenorrhoea, galactorrhoea, and ovulation disorder.
QT Interval Prolongation — SYMBYAX was associated with a statistically significantly greater mean increase in QTcF interval (8.2 msec [95% CI 6.2, 10.2]) compared with placebo. No patients developed QTc increases ≥ 60 msec or QTc ≥ 480 msec [see WARNINGS AND PRECAUTIONS].
The following adverse reactions have been identified during post-approval use of SYMBYAX. Because these reactions are reported voluntarily from a population of uncertain size, it is difficult to reliably estimate their frequency or evaluate a causal relationship to drug exposure.
Adverse reactions reported since market introduction that were temporally (but not necessarily causally) related to SYMBYAX therapy include the following: rhabdomyolysis and venous thromboembolic events (including pulmonary embolism and deep venous thrombosis).
1 This term represents a serious adverse event but does not meet the definition for adverse drug reactions. It is included here because of its seriousness.
2Adjusted for gender.
3These terms represent serious adverse events but do not meet the definition for adverse drug reactions. They are included here because of their seriousness.
Read the Symbyax (olanzapine and fluoxetine) Side Effects Center for a complete guide to possible side effects
The risks of using SYMBYAX in combination with other drugs have not been extensively evaluated in systematic studies. The drug-drug interactions sections of fluoxetine and olanzapine are applicable to SYMBYAX. As with all drugs, the potential for interaction by a variety of mechanisms (e.g., pharmacodynamic, pharmacokinetic drug inhibition or enhancement, etc.) is a possibility. In evaluating individual cases, consideration should be given to using lower initial doses of the concomitantly administered drugs, using conservative titration schedules, and monitoring of clinical status [see CLINICAL PHARMACOLOGY].
Monoamine Oxidase Inhibitors (MAOIs)
CNS Acting Drugs
Caution is advised if the concomitant administration of SYMBYAX and other CNS-active drugs is required. In evaluating individual cases, consideration should be given to using lower initial doses of the concomitantly administered drugs, using conservative titration schedules, and monitoring of clinical status [see CLINICAL PHARMACOLOGY].
Drugs that Interfere with Hemostasis (e.g., NSAIDs, Aspirin, Warfarin)
Serotonin release by platelets plays an important role in hemostasis. Epidemiological studies of the case-control and cohort design that have demonstrated an association between use of psychotropic drugs that interfere with serotonin reuptake and the occurrence of upper gastrointestinal bleeding have also shown that concurrent use of an NSAID or aspirin may potentiate this risk of bleeding. Altered anticoagulant effects, including increased bleeding, have been reported when SNRIs or SSRIs are coadministered with warfarin [see WARNINGS AND PRECAUTIONS]. Warfarin (20 mg single dose) did not affect olanzapine pharmacokinetics. Single doses of olanzapine did not affect the pharmacokinetics of warfarin. Patients receiving warfarin therapy should be carefully monitored when SYMBYAX is initiated or discontinued.
Electroconvulsive Therapy (ECT)
There are no clinical studies establishing the benefit of the combined use of ECT and fluoxetine. There have been rare reports of prolonged seizures in patients on fluoxetine receiving ECT treatment [see WARNINGS AND PRECAUTIONS].
Potential for Other Drugs to Affect SYMBYAX
Benzodiazepines — Co-administration of diazepam with olanzapine potentiated the orthostatic hypotension observed with olanzapine.
Inducers of 1A2 — Carbamazepine therapy (200 mg BID) causes an approximate 50% increase in the clearance of olanzapine. This increase is likely due to the fact that carbamazepine is a potent inducer of CYP1A2 activity. Higher daily doses of carbamazepine may cause an even greater increase in olanzapine clearance [see DRUG INTERACTIONS].
Alcohol — Ethanol (45 mg/70 kg single dose) did not have an effect on olanzapine pharmacokinetics.
Inhibitors of CYP1A2 — Fluvoxamine decreases the clearance of olanzapine. This results in a mean increase in olanzapine Cmax following fluvoxamine administration of 54% in female nonsmokers and 77% in male smokers. The mean increase in olanzapine AUC is 52% and 108%, respectively. Lower doses of the olanzapine component of SYMBYAX should be considered in patients receiving concomitant treatment with fluvoxamine.
The Effect of Other Drugs on Olanzapine — Fluoxetine, an inhibitor of CYP2D6, decreases olanzapine clearance a small amount [see CLINICAL PHARMACOLOGY]. Agents that induce CYP1A2 or glucuronyl transferase enzymes, such as omeprazole and rifampin, may cause an increase in olanzapine clearance. The effect of CYP1A2 inhibitors, such as fluvoxamine and some fluoroquinolone antibiotics, on SYMBYAX has not been evaluated. Although olanzapine is metabolized by multiple enzyme systems, induction or inhibition of a single enzyme may appreciably alter olanzapine clearance. Therefore, a dosage increase (for induction) or a dosage decrease (for inhibition) may need to be considered with specific drugs.
Potential for SYMBYAX to Affect Other Drugs
Pimozide — Concomitant use of SYMBYAX and pimozide is contraindicated. Pimozide can prolong the QT interval. SYMBYAX can increase the level of pimozide through inhibition of CYP2D6. SYMBYAX can also prolong the QT interval. Clinical studies of pimozide with other antidepressants demonstrate an increase in drug interaction or QTc prolongation. While a specific study with pimozide and SYMBYAX has not been conducted, the potential for drug interactions or QTc prolongation warrants restricting the concurrent use of pimozide and SYMBYAX [see CONTRAINDICATIONS, and WARNINGS AND PRECAUTIONS].
Carbamazepine — Patients on stable doses of carbamazepine have developed elevated plasma anticonvulsant concentrations and clinical anticonvulsant toxicity following initiation of concomitant fluoxetine treatment.
Alcohol — The coadministration of ethanol with SYMBYAX may potentiate sedation and orthostatic hypotension.
Thioridazine — Thioridazine should not be administered with SYMBYAX or administered within a minimum of 5 weeks after discontinuation of SYMBYAX, because of the risk of QT prolongation [see CONTRAINDICATIONS, and WARNINGS AND PRECAUTIONS].
In a study of 19 healthy male subjects, which included 6 slow and 13 rapid hydroxylators of debrisoquin, a single 25 mg oral dose of thioridazine produced a 2.4-fold higher Cmax and a 4.5-fold higher AUC for thioridazine in the slow hydroxylators compared with the rapid hydroxylators. The rate of debrisoquin hydroxylation is felt to depend on the level of CYP2D6 isozyme activity. Thus, this study suggests that drugs that inhibit CYP2D6, such as certain SSRIs, including fluoxetine, will produce elevated plasma levels of thioridazine [see CONTRAINDICATIONS].
Thioridazine administration produces a dose-related prolongation of the QTc interval, which is associated with serious ventricular arrhythmias, such as torsades de pointes-type arrhythmias and sudden death. This risk is expected to increase with fluoxetine-induced inhibition of thioridazine metabolism [see CONTRAINDICATIONS].
Due to the risk of serious ventricular arrhythmias and sudden death potentially associated with elevated thioridazine plasma levels, thioridazine should not be administered with fluoxetine or within a minimum of 5 weeks after fluoxetine has been discontinued [see CONTRAINDICATIONS].
Tricyclic Antidepressants (TCAs) — Single doses of olanzapine did not affect the pharmacokinetics of imipramine or its active metabolite desipramine.
In 2 fluoxetine studies, previously stable plasma levels of imipramine and desipramine have increased > 2- to 10fold when fluoxetine has been administered in combination. This influence may persist for 3 weeks or longer after fluoxetine is discontinued. Thus, the dose of TCA may need to be reduced and plasma TCA concentrations may need to be monitored temporarily when SYMBYAX is coadministered or has been recently discontinued [see WARNINGS AND PRECAUTIONS and CLINICAL PHARMACOLOGY].
Levodopa and Dopamine Agonists — The olanzapine component of SYMBYAX may antagonize the effects of levodopa and dopamine agonists.
Benzodiazepines — Multiple doses of olanzapine did not influence the pharmacokinetics of diazepam and its active metabolite N-desmethyldiazepam.
When concurrently administered with fluoxetine, the half-life of diazepam may be prolonged in some patients [see CLINICAL PHARMACOLOGY]. Coadministration of alprazolam and fluoxetine has resulted in increased alprazolam plasma concentrations and in further psychomotor performance decrement due to increased alprazolam levels.
Clozapine — Elevation of blood levels of clozapine has been observed in patients receiving concomitant fluoxetine.
Haloperidol — Elevation of blood levels of haloperidol has been observed in patients receiving concomitant fluoxetine.
Phenytoin — Patients on stable doses of phenytoin have developed elevated plasma levels of phenytoin with clinical phenytoin toxicity following initiation of concomitant fluoxetine.
Drugs Metabolized by CYP2D6 — In vitro studies utilizing human liver microsomes suggest that olanzapine has little potential to inhibit CYP2D6. Thus, olanzapine is unlikely to cause clinically important drug interactions mediated by this enzyme.
Fluoxetine inhibits the activity of CYP2D6 and may make individuals with normal CYP2D6 metabolic activity resemble a poor metabolizer. Coadministration of fluoxetine with other drugs that are metabolized by CYP2D6, including certain antidepressants (e.g., TCAs), antipsychotics (e.g., phenothiazines and most atypicals), and antiarrhythmics (e.g., propafenone, flecainide, and others) should be approached with caution. Therapy with medications that are predominantly metabolized by the CYP2D6 system and that have a relatively narrow therapeutic index should be initiated at the low end of the dose range if a patient is receiving fluoxetine concurrently or has taken it in the previous 5 weeks. If fluoxetine is added to the treatment regimen of a patient already receiving a drug metabolized by CYP2D6, the need for a decreased dose of the original medication should be considered. Drugs with a narrow therapeutic index represent the greatest concern (including but not limited to, flecainide, propafenone, vinblastine, and TCAs).
Drugs Metabolized by CYP3A — In vitro studies utilizing human liver microsomes suggest that olanzapine has little potential to inhibit CYP3A. Thus, olanzapine is unlikely to cause clinically important drug interactions mediated by these enzymes.
In an in vivo interaction study involving the coadministration of fluoxetine with single doses of terfenadine (a CYP3A substrate), no increase in plasma terfenadine concentrations occurred with concomitant fluoxetine. In addition, in vitro studies have shown ketoconazole, a potent inhibitor of CYP3A activity, to be at least 100 times more potent than fluoxetine or norfluoxetine as an inhibitor of the metabolism of several substrates for this enzyme, including astemizole, cisapride, and midazolam. These data indicate that fluoxetine's extent of inhibition of CYP3A activity is not likely to be of clinical significance.
Effect of Olanzapine on Drugs Metabolized by Other CYP Enzymes — In vitro studies utilizing human liver microsomes suggest that olanzapine has little potential to inhibit CYP1A2, CYP2C9, and CYP2C19. Thus, olanzapine is unlikely to cause clinically important drug interactions mediated by these enzymes.
Lithium — Multiple doses of olanzapine did not influence the pharmacokinetics of lithium.
There have been reports of both increased and decreased lithium levels when lithium was used concomitantly with fluoxetine. Cases of lithium toxicity and increased serotonergic effects have been reported. Lithium levels should be monitored in patients taking SYMBYAX concomitantly with lithium [see WARNINGS AND PRECAUTIONS].
Drugs Tightly Bound to Plasma Proteins — The in vitro binding of SYMBYAX to human plasma proteins is similar to the individual components. The interaction between SYMBYAX and other highly protein-bound drugs has not been fully evaluated. Because fluoxetine is tightly bound to plasma protein, the administration of fluoxetine to a patient taking another drug that is tightly bound to protein (e.g., Coumadin, digitoxin) may cause a shift in plasma concentrations potentially resulting in an adverse effect. Conversely, adverse effects may result from displacement of protein-bound fluoxetine by other tightly bound drugs [see CLINICAL PHARMACOLOGY].
Valproate — In vitro studies using human liver microsomes determined that olanzapine has little potential to inhibit the major metabolic pathway, glucuronidation, of valproate. Further, valproate has little effect on the metabolism of olanzapine in vitro. Thus, a clinically significant pharmacokinetic interaction between olanzapine and valproate is unlikely.
Biperiden — Multiple doses of olanzapine did not influence the pharmacokinetics of biperiden.
Theophylline — Multiple doses of olanzapine did not affect the pharmacokinetics of theophylline or its metabolites.
Drugs that Prolong the QT Interval
Do not use SYMBYAX in combination with thioridazine or pimozide. Use SYMBYAX with caution in combination with other drugs that cause QT prolongation. These include: specific antipsychotics (e.g., ziprasidone, iloperidone, chlorpromazine, mesoridazine, droperidol); specific antibiotics (e.g., erythromycin, gatifloxacin, moxifloxacin, sparfloxacin); Class 1A antiarrhythmic medications (e.g., quinidine, procainamide); Class III antiarrhythmics (e.g., amiodarone, sotalol); and others (e.g., pentamidine, levomethadyl acetate, methadone, halofantrine, mefloquine, dolasetron mesylate, probucol or tacrolimus). Fluoxetine is primarily metabolized by CYP2D6. Concomitant treatment with CYP2D6 inhibitors can increase the concentration of fluoxetine. Concomitant use of other highly protein-bound drugs can increase the concentration of fluoxetine [see CONTRAINDICATIONS, WARNINGS AND PRECAUTIONS, and CLINICAL PHARMACOLOGY].
Drug Abuse And Dependence
SYMBYAX, as with fluoxetine and olanzapine, has not been systematically studied in humans for its potential for abuse, tolerance, or physical dependence. While the clinical studies did not reveal any tendency for any drug-seeking behavior, these observations were not systematic, and it is not possible to predict on the basis of this limited experience the extent to which a CNS-active drug will be misused, diverted, and/or abused once marketed. Consequently, physicians should carefully evaluate patients for history of drug abuse and follow such patients closely, observing them for signs of misuse or abuse of SYMBYAX (e.g., development of tolerance, incrementation of dose, drug-seeking behavior).
In studies in rats and rhesus monkeys designed to assess abuse and dependence potential, olanzapine alone was shown to have acute depressive CNS effects but little or no potential of abuse or physical dependence at oral doses up to 15 (rat) and 8 (monkey) times the MRHD (20 mg) on a mg/m² basis.
Read the Symbyax Drug Interactions Center for a complete guide to possible interactions
Last reviewed on RxList: 8/7/2013
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