Quetiapine Fumarate (Page 7 of 11)

8.5 Geriatric Use

Of the approximately 3700 patients in clinical studies with quetiapine, 7% (232) were 65 years of age or over. In general, there was no indication of any different tolerability of quetiapine in the elderly compared to younger adults. Nevertheless, the presence of factors that might decrease pharmacokinetic clearance, increase the pharmacodynamic response to quetiapine, or cause poorer tolerance or orthostasis, should lead to consideration of a lower starting dose, slower titration, and careful monitoring during the initial dosing period in the elderly. The mean plasma clearance of quetiapine was reduced by 30% to 50% in elderly patients when compared to younger patients [ see Clinical Pharmacology (12.3)and Dosage and Administration (2.3) ].

8.6 Renal Impairment

Clinical experience with quetiapine in patients with renal impairment is limited [see Clinical Pharmacology (12.3)].

8.7 Hepatic Impairment

Since quetiapine is extensively metabolized by the liver, higher plasma levels are expected in patients with hepatic impairment. In this population, a low starting dose of 25 mg/day is recommended and the dose may be increased in increments of 25 mg/day — 50 mg/day [see Dosage and Administration (2.4) and Clinical Pharmacology (12.3)] .

9 DRUG ABUSE AND DEPENDENCE

9.1 Controlled Substance

Quetiapine is not a controlled substance.

9.2 Abuse

Quetiapine has not been systematically studied, in animals or humans, for its potential for abuse, tolerance or physical dependence. While the clinical trials 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, patients should be evaluated carefully for a history of drug abuse, and such patients should be observed closely for signs of misuse or abuse of quetiapine, e.g., development of tolerance, increases in dose, drug-seeking behavior.

10 OVERDOSAGE

10.1 Human Experience

In clinical trials, survival has been reported in acute overdoses of up to 30 grams of quetiapine. Most patients who overdosed experienced no adverse reactions or recovered fully from the reported reactions. Death has been reported in a clinical trial following an overdose of 13.6 grams of quetiapine alone. In general, reported signs and symptoms were those resulting from an exaggeration of the drug’s known pharmacological effects, i.e., drowsiness and sedation, tachycardia and hypotension. Patients with pre-existing severe cardiovascular disease may be at an increased risk of the effects of overdose [see Warnings and Precautions (5.11)]. One case, involving an estimated overdose of 9600 mg, was associated with hypokalemia and first degree heart block. In post-marketing experience, there were cases reported of QT prolongation with overdose. There were also very rare reports of overdose of quetiapine alone resulting in death or coma.

10.2 Management of Overdosage

In case of acute overdosage, establish and maintain an airway and ensure adequate oxygenation and ventilation. Gastric lavage (after intubation, if patient is unconscious) and administration of activated charcoal together with a laxative should be considered. The possibility of obtundation, seizure or dystonic reaction of the head and neck following overdose may create a risk of aspiration with induced emesis. Cardiovascular monitoring should commence immediately and should include continuous electrocardiographic monitoring to detect possible arrhythmias. If antiarrhythmic therapy is administered, disopyramide, procainamide and quinidine carry a theoretical hazard of additive QT-prolonging effects when administered in patients with acute overdosage of quetiapine. Similarly it is reasonable to expect that the alpha- adrenergic-blocking properties of bretylium might be additive to those of quetiapine, resulting in problematic

hypotension.

There is no specific antidote to quetiapine. Therefore, appropriate supportive measures should be instituted. The possibility of multiple drug involvement should be considered. Hypotension and circulatory collapse should be treated with appropriate measures such as intravenous fluids and/or sympathomimetic agents (epinephrine and dopamine should not be used, since beta stimulation may worsen hypotension in the setting of quetiapine-induced alpha blockade). In cases of severe extrapyramidal symptoms, anticholinergic medication should be administered. Close medical supervision and monitoring should continue until the patient recovers.

11 DESCRIPTION

Quetiapinefumarate is a psychotropic agent belonging to a chemical class, the dibenzothiazepine derivatives. The chemical designation is 2-[2-(4-dibenzo [ b,f ] [1,4]thiazepin-11-yl-1-piperazinyl) ethoxy]-ethanol fumarate (2:1) (salt). It is present in tablets as the fumarate salt. All doses and tablet strengths are expressed as milligrams of base, not as fumarate salt. Its molecular formula is C42H50N6O4S2•C4H4O4 and it has a molecular weight of 883.11 (fumarate salt). The structural formula is:

Structure
(click image for full-size original)

Quetiapine fumarate is a white to off-white crystalline powder which is moderately soluble in water.

Quetiapine tablets, USP is supplied for oral administration as 25 mg (round peach), 50 mg (round, white), 100 mg (round yellow), 150 mg (round, off white to light yellow), 200 mg (round, white), 300 mg (capsule-shaped, white), and 400 mg (capsule-shaped, yellow) tablets.

Inactive ingredients are povidone, dibasic dicalcium phosphate dihydrate, microcrystalline cellulose, sodium starch glycolate, lactose monohydrate, magnesium stearate, hypromellose, polyethylene glycol and titanium dioxide. The 25 mg tablets contain red iron oxide and yellow iron oxide and the 100 mg, 150 mg and 400 mg tablets contain only yellow iron oxide.

The USP dissolution test is pending.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

The mechanism of action of quetiapine is unknown. However, it has been proposed that the efficacy of quetiapine in schizophrenia and its mood stabilizing properties in bipolar depression and mania are mediated through a combination of dopamine type 2 (D2) and serotonin type 2 (5HT2) antagonism. Antagonism at receptors other than dopamine and 5HT2 with similar receptor affinities may explain some of the other effects of quetiapine.

Quetiapine’s antagonism of histamine H1 receptors may explain the somnolence observed with this drug.

Quetiapine’s antagonism of adrenergic α 1 receptors may explain the orthostatic hypotension observed with dis drug.

12.2 Pharmacodynamics

Quetiapineis an antagonist at multiple neurotransmitter receptors in the brain: serotonin 5HT1A and 5HT2 (IC50s=717 & 148nM, respectively), dopamine D1 and D2 (IC50s=1268 & 329nM, respectively), histamine H1 (IC50=30nM), and adrenergic α 1 and α 2 receptors (IC50s=94 & 271nM, respectively). Quetiapine has no appreciable affinity at cholinergic muscarinic and benzodiazepine receptors (IC50s>5000 nM).

Effect on QT Interval

In clinical trials quetiapine was not associated with a persistent increase in QT intervals. However, the QT effect was not systematically evaluated in a thorough QT study. In post marketing experience there were cases reported of QT prolongation in patients who overdosed on quetiapine [see Overdosage (10.1)] , in patients with concomitant illness, and in patients taking medicines known to cause electrolyte imbalance or increase QT interval.

12.3 Pharmacokinetics

Adults

Quetiapine fumarate activity is primarily due to the parent drug. The multiple-dose pharmacokinetics of quetiapine are dose-proportional within the proposed clinical dose range, and quetiapine accumulation is predictable upon multiple dosing. Elimination of quetiapine is mainly via hepatic metabolism with a mean terminal half-life of about 6 hours within the proposed clinical dose range. Steady-state concentrations are expected to be achieved within two days of dosing. Quetiapine is unlikely to interfere with the metabolism of drugs metabolized by cytochrome P450 enzymes.

Children and Adolescents

At steady-state the pharmacokinetics of the parent compound, in children and adolescents (10-17 years of age), were similar to adults. However, when adjusted for dose and weight, AUC and Cmax of the parent compound were 41% and

39% lower, respectively, in children and adolescents than in adults. For the active metabolite, norquetiapine, AUC and

Cmax were 45% and 31% higher, respectively, in children and adolescents than in adults. When adjusted for dose and weight, the pharmacokinetics of the metabolite, norquetiapine, was similar between children and adolescents and adults [see Use in Specific Populations (8.4)] .

Absorption

Quetiapine fumarate is rapidly absorbed after oral administration, reaching peak plasma concentrations in 1.5 hours. The tablet formulation is 100% bioavailable relative to solution. The bioavailability of quetiapine is marginally affected by administration with food, with Cmax and AUC values increased by 25% and 15%, respectively.

D i stribution

Quetiapine is widely distributed throughout the body with an apparent volume of distribution of 10±4 L/kg. It is 83% bound to plasma proteins at therapeutic concentrations. In vitro , quetiapine did not affect the binding of warfarin or diazepam to human serum albumin. In turn, neither warfarin nor diazepam altered the binding of quetiapine.

Metabolism and Elimination

Following a single oral dose of 14C-quetiapine, less than 1% of the administered dose was excreted as unchanged drug, indicating that quetiapine is highly metabolized. Approximately 73% and 20% of the dose was recovered in the urine and feces, respectively.

Quetiapine is extensively metabolized by the liver. The major metabolic pathways are sulfoxidation to the sulfoxide metabolite and oxidation to the parent acid metabolite; both metabolites are pharmacologically inactive. In vitro studies using human liver microsomes revealed that the cytochrome P450 3A4 isoenzyme is involved in the metabolism of quetiapine to its major, but inactive, sulfoxide metabolite and in the metabolism of its active metabolite N-desalkyl quetiapine.

Age

Oral clearance of quetiapine was reduced by 40% in elderly patients (≥ 65 years, n=9) compared to young patients (n=12), and dosing adjustment may be necessary [see Dosage and Administration (2.3)].

G ender

There is no gender effect on the pharmacokinetics of quetiapine.

Race

There is no race effect on the pharmacokinetics of quetiapine.

Smoking

Smoking has no effect on the oral clearance of quetiapine.

Renal Insufficiency

Patients with severe renal impairment (Clcr=10-30 mL/min/1.73 m2, n=8) had a 25% lower mean oral clearance than normal subjects (Clcr > 80 mL/min/1.73 m2, n=8), but plasma quetiapine concentrations in the subjects with renal insufficiency were within the range of concentrations seen in normal subjects receiving the same dose. Dosage adjustment is therefore not needed in these patients [see Use in Specific Populations (8.6)] .

H epatic Insufficiency

Hepatically impaired patients (n=8) had a 30% lower mean oral clearance of quetiapine than normal subjects. In two of the 8 hepatically impaired patients, AUC and Cmax were 3 times higher than those observed typically in healthy subjects. Since quetiapine is extensively metabolized by the liver, higher plasma levels are expected in the hepatically impaired population, and dosage adjustment may be needed [s ee Dosage and Administration (2.4) and Use in Specific Populations (8.7)] .

D rug-Drug Interaction Studies

The in vivo assessments of effect of other drugs on the pharmacokinetics of quetiapine are summarized in Table 17 [see Dosage and Administration (2.5 and 2.6) and Drug Interactions (7.1)] .

T able 17: The Effect of Other Drugs on the Pharmacokinetics of Quetiapine

Coadministered drug Dose schedules Effect on quetiapine pharmacokinetics
Coadministered drug Quetiapine
Phenytoin 100 mg three times daily 250 mg three times daily 5 fold Increase in oral clearance
Divalproex 500 mg twice daily 150 mg twice daily 17% increase mean max plasma concentration at steady state. No effect on absorption or mean oral clearance
Thioridazine 200 mg twice daily 300 mg twice daily 65% increase in oral clearance
Cimetidine 400 mg three times daily for 4 days 150 mg three times daily 20% decrease in mean oral clearance
Ketoconazole (potent CYP 3A4 inhibitor) 200 mg once daily for 4 days 25 mg single dose 84% decrease in oral clearance resulting in a 6.2 fold increase in AUC of quetiapine
Fluoxetine 60 mg once daily 300 mg twice daily No change in steady state PK
Imipramine 75 mg twice daily 300 mg twice daily No change in steady state PK
Haloperidol 7.5 mg twice daily 300 mg twice daily No change in steady state PK
Risperidone 3 mg twice daily 300 mg twice daily No change in steady state PK

I n vitro enzyme inhibition data suggest that quetiapine and 9 of its metabolites would have little inhibitory effect on in vivo metabolism mediated by cytochromes CYP 1A2, 2C9, 2C19, 2D6 and 3A4. Quetiapine at doses of 750 mg/day did not affect the single dose pharmacokinetics of antipyrine, lithium or lorazepam (Table 18) [see Drug Interactions (7.2)] .

T able 18: The Effect of Quetiapine on the Pharmacokinetics of Other Drugs

Coadministered drug Dose schedules Effect on other drugs pharmacokinetics
Coadministered drug Quetiapine
Lorazepam 2 mg, single dose 250 mg three times daily Oral clearance of lorazepam reduced by 20%
Divalproex 500 mg twice daily 150 mg twice daily Cmax and AUC of free valproic acid at steady- state was decreased by 10-12%
Lithium Up to 2400 mg/day given in twice daily doses 250 mg three times daily No effect on steady-state pharmacokinetics of lithium
Antipyrine 1 g, single dose 250 mg three times daily No effect on clearance of antipyrine or urinary recovery of its metabolites

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