ulation may worsen hypotension in the setting of quetiapine-induced α 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
SEROQUEL XR (quetiapine fumarate) 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:
Quetiapine fumarate is a white to off-white crystalline powder which is moderately soluble in water.
SEROQUEL XR is supplied for oral administration as 50 mg (peach), 150 mg (white), 200 mg (yellow), 300 mg (pale yellow), and 400 mg (white). All tablets are capsule shaped and film coated.
Inactive ingredients for SEROQUEL XR are lactose monohydrate, microcrystalline cellulose, sodium citrate, hypromellose, and magnesium stearate. The film coating for all SEROQUEL XR tablets contain hypromellose, polyethylene glycol 400 and titanium dioxide. In addition yellow iron oxide (50, 200 and 300 mg tablets) and red iron oxide (50 mg tablets) are included in the film coating of specific strengths.
Each 50 mg tablet contains 58 mg of quetiapine fumarate equivalent to 50 mg quetiapine. Each 150 mg tablet contains 173 mg of quetiapine fumarate equivalent to 150 mg quetiapine. Each 200 mg tablet contains 230 mg of quetiapine fumarate equivalent to 200 mg quetiapine. Each 300 mg tablet contains 345 mg of quetiapine fumarate equivalent to 300 mg quetiapine. Each 400 mg tablet contains 461 mg of quetiapine fumarate equivalent to 400 mg quetiapine.
12 CLINICAL PHARMACOLOGY
12.1 Mechanism of Action
The mechanism of action of SEROQUEL XR, as with other drugs having efficacy in the treatment of schizophrenia, bipolar disorder and major depressive disorder (MDD), is unknown. However, it has been proposed that the efficacy of SEROQUEL XR in schizophrenia is mediated through a combination of dopamine type 2 (D2) and serotonin type 2A (5HT2A) antagonism. The active metabolite, N-desalkyl quetiapine (norquetiapine), has similar activity at D2, but greater activity at 5HT2A receptors, than the parent drug (quetiapine). Quetiapine’s efficacy in bipolar depression and MDD may partly be explained by the high affinity and potent inhibitory effects that norquetiapine exhibits for the norepinephrine transporter.
Antagonism at receptors other than dopamine and serotonin with similar or greater affinities may explain some of the other effects of quetiapine and norquetiapine: antagonism at histamine H1 receptors may explain the somnolence, antagonism at adrenergic α1b receptors may explain the orthostatic hypotension, and antagonism at muscarinic M1 receptors may explain the anticholinergic effects.
12.2 Pharmacodynamics
Quetiapine and norquetiapine have affinity for multiple neurotransmitter receptors including dopamine D1 and D2, serotonin 5HT1A and 5HT2A, histamine H1, muscarinic M1, and adrenergic α1b and α2 receptors. Quetiapine differs from norquetiapine in having no appreciable affinity for muscarinic M1 r
