Quetiapine Fumarate 50 mg Tablet, 90-count — NDC 80425-0186-3 (Billing 80425-0186-03)

12. Clinical Pharmacology

12.1Mechanism of Action The mechanism of action of quetiapine in the listed indications is unclear. However, the efficacy of quetiapine in these indications could be mediated through a combination of dopamine type 2 (D2) and serotonin type 2 (5HT2) antagonism. The active metabolite, N-desalkyl quetiapine (norquetiapine), has similar activity at D2, but greater activity at 5HT2A receptors, than the parent drug (quetiapine).

12.2Pharmacodynamics Quetiapine and its metabolite, norquetiapine, have affinity for multiple neurotransmitter receptors with norquetiapine binding with higher affinity than quetiapine in general. The Ki values for quetiapine and norquetiapine at the dopamine D1 are 428/99.8 nM, at D2 626/489nM, at serotonin 5HT1A 1040/191 nM at 5HT2A 38/2.9 nM, at histamine H1 4.4/1.1 nM, at muscarinic M1 1086/38.3 nM, and at adrenergic α1b 14.6/46.4 nM and, at α2 receptors 617/1290 nM, respectively. Quetiapine and norquetiapine lack appreciable affinity to the benzodiazepine receptors.

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.

12.3Pharmacokinetics Adults Quetiapine 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 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.

Distribution 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 t… [Excerpted — this section continues on DailyMed.]

14. Clinical Studies

14.1Schizophrenia Short-term Trials-Adults The efficacy of quetiapine in the treatment of schizophrenia was established in 3 short-term (6-week) controlled trials of inpatients with schizophrenia who met DSM III-R criteria for schizophrenia. Although a single fixed dose haloperidol arm was included as a comparative treatment in one of the three trials, this single haloperidol dose group was inadequate to provide a reliable and valid comparison of quetiapine and haloperidol. Several instruments were used for assessing psychiatric signs and symptoms in these studies, among them the Brief Psychiatric Rating Scale (BPRS), a multi-item inventory of general psychopathology traditionally used to evaluate the effects of drug treatment in schizophrenia.

The BPRS psychosis cluster (conceptual disorganization, hallucinatory behavior, suspiciousness, and unusual thought content) is considered a particularly useful subset for assessing actively psychotic schizophrenic patients. A second traditional assessment, the Clinical Global Impression (CGI), reflects the impression of a skilled observer, fully familiar with the manifestations of schizophrenia, about the overall clinical state of the patient. The results of the trials follow: 1.

In a 6-week, placebo-controlled trial (n=361) (Study 1) involving 5 fixed doses of quetiapine (75 mg/day, 150 mg/day, 300 mg/day, 600 mg/day and 750 mg/day given in divided doses three times per day), the 4 highest doses of quetiapine were generally superior to placebo on the BPRS total score, the BPRS psychosis cluster and the CGI severity score, with the maximal effect seen at 300 mg/day, and the effects of doses of 150 mg/day to 750 mg/day were generally indistinguishable. 2. In a 6-week, placebo-controlled trial (n=286) (Study 2) involving titration of quetiapine in high (up to 750 mg/day given in divided doses three times per day) and low (up to 250 mg/day given in divided doses three times per day) doses, only the high dose quetiapine group (mean dose, 500 mg/day) was superior to placebo on the BPRS total score, the BPRS psychosis cluster, and the CGI severity score.

3. In a 6-week dose and dose regimen comparison trial (n=618) (Study 3) involving two fixed doses of quetiapine (450 mg/day given in divided doses both twice daily and three times daily and 50 mg/day given in divided doses twice daily), only the 450 mg/day (225 mg given twice daily) dose group was superior to the 50 mg/day (25 mg given twice daily) quetiapine dose group on the BPRS total score, the BPRS psychosis cluster, and the CGI severity score. The primary efficacy results of these three studies in the treatment of schizophrenia in adults is presented in Table 19.

Examination of population subsets (race, gender, and age) did not reveal any differential responsiveness on the basis of race or gender, with an apparently greater effect in patients under the age of 40 years compared to those older than 40. The clinical significance of this finding is unknown. Adolescents (ages 13 to 17) The efficacy of quetiapine in the treatment of schizophrenia in adolescents (13 to 17 years of age) was demonstrated in a 6-week, double-blind, placebo-controlled trial (Study 4).

Patients who met DSM-IV diagnostic criteria for schizophrenia were randomized into one of three treatment groups: Quetiapine 400 mg/day (n = 73), Quetiapine 800 mg/day (n = 74), or placebo (n = 75). Study medication was initiated at 50 mg/day and on day 2 increased to 100 mg/per day (divided and given two or three times per day). Subsequently, the dose was titrated to the target dose of 400 mg/day or 800 mg/day using increments of 100 mg/day, divided and given two or three times daily.

The primary efficacy variable was the mean change from baseline in total Positive and Negative Syndrome Scale (PANSS). Quetiapine at 400 mg/day and 800 mg/day was superior to placebo in the reduction of PANSS total score. The primary efficacy results of this study in the treatmen… [Excerpted — this section continues on DailyMed.]

13. Non Clinical Toxicology

13.1Carcinogenesis, Mutagenesis, Impairment of Fertility Carcinogenesis Carcinogenicity studies were conducted in C57BL mice and Wistar rats. Quetiapine was administered in the diet to mice at doses of 20, 75, 250, and 750 mg/kg and to rats by gavage at doses of 25, 75, and 250 mg/kg for two years. These doses are equivalent to 0.1, 0.5, 1.5, and 4.5 times the MRHD of 800 mg/day based on mg/m2 body surface area (mice) or 0.3, 1, and 3 times the MRHD based on mg/m2 body surface area (rats).

There were statistically significant increases in thyroid gland follicular adenomas in male mice at doses 1.5 and 4.5 times the MRHD on mg/m2 body surface area and in male rats at a dose of 3 times the MRHD on mg/m2 body surface area. Mammary gland adenocarcinomas were statistically significantly increased in female rats at all doses tested (0.3, 1, and 3 times the MRHD based on mg/m2 body surface area). Thyroid follicular cell adenomas may have resulted from chronic stimulation of the thyroid gland by thyroid stimulating hormone (TSH) resulting from enhanced metabolism and clearance of thyroxine by rodent liver.

Changes in TSH, thyroxine, and thyroxine clearance consistent with this mechanism were observed in subchronic toxicity studies in rat and mouse and in a 1-year toxicity study in rat; however, the results of these studies were not definitive. The relevance of the increases in thyroid follicular cell adenomas to human risk, through whatever mechanism, is unknown. Antipsychotic drugs have been shown to chronically elevate prolactin levels in rodents.

Serum measurements in a 1-year toxicity study showed that quetiapine increased median serum prolactin levels a maximum of 32- and 13-fold in male and female rats, respectively. Increases in mammary neoplasms have been found in rodents after chronic administration of other antipsychotic drugs and are considered to be prolactin-mediated. The relevance of this increased incidence of prolactin-mediated mammary gland tumors in rats to human risk is unknown [see Warnings and Precautions (5.15)].

Mutagenesis Quetiapine was not mutagenic or clastogenic in standard genotoxicity tests. The mutagenic potential of quetiapine was tested in the in vitro Ames bacterial gene mutation assay and in the in vitro mammalian gene mutation assay in Chinese Hamster Ovary cells. The clastogenic potential of quetiapine was tested in the in vitro chromosomal aberration assay in cultured human lymphocytes and in the in vivo bone marrow micronucleus assay in rats up to 500 mg/kg, which is 6 times the MRHD based on mg/m2 body surface area.

Impairment of Fertility Quetiapine decreased mating and fertility in male Sprague-Dawley rats at oral doses of 50 and 150 mg/kg or approximately 1 and 3 times the MRHD of 800 mg/day based on mg/m2 body surface area. Drug- related effects included increases in interval to mate and in the number of matings required for successful impregnation. These effects continued to be observed at 3 times the MRHD even after a two-week period without treatment.

The no- effect dose for impaired mating and fertility in male rats was 25 mg/kg, or 0.3 times the MRHD based on mg/m2 body surface area. Quetiapine adversely affected mating and fertility in female Sprague-Dawley rats at an oral dose approximately 1 times the MRHD of 800 mg/day based on mg/m2 body surface area. Drug-related effects included decreases in matings and in matings resulting in pregnancy, and an increase in the interval to mate.

An increase in irregular estrus cycles was observed at doses of 10 and 50 mg/kg, or approximately 0.1 and 1 times the MRHD of 800 mg/day based on mg/m2 body surface area. The no-effect dose in female rats was 1 mg/kg, or 0.01 times the MRHD of 800 mg/day based on mg/m2 body surface area.

13.2Animal Toxicology and/or Pharmacology Quetiapine caused a dose-related increase in pigment deposition in thyroid gland in rat toxicity studies which were 4 weeks in duration or longer and… [Excerpted — this section continues on DailyMed.]