Aripiprazole (Page 8 of 11)

10.2 Management of Overdosage

No specific information is available on the treatment of overdose with aripiprazole tablets. An electrocardiogram should be obtained in case of overdosage and if QT interval prolongation is present, cardiac monitoring should be instituted. Otherwise, management of overdose should concentrate on supportive therapy, maintaining an adequate airway, oxygenation and ventilation, and management of symptoms. Close medical supervision and monitoring should continue until the patient recovers.
Charcoal: In the event of an overdose of aripiprazole tablets, an early charcoal administration may be useful in partially preventing the absorption of aripiprazole. Administration of 50 g of activated charcoal, one hour after a single 15 mg oral dose of aripiprazole tablets, decreased the mean AUC and C max of aripiprazole by 50%.
Hemodialysis: Although there is no information on the effect of hemodialysis in treating an overdose with aripiprazole tablets, hemodialysis is unlikely to be useful in overdose management since aripiprazole is highly bound to plasma proteins.

11 DESCRIPTION

Aripiprazole is a psychotropic drug that is available as aripiprazole tablets. Aripiprazole tablets are chemically designated as 7-[4-[4-(2,3-Dichlorophenyl)-1-piperazinyl]butoxy]-3,4-dihydro-2(1H)-quinolinone. The empirical formula is C 23 H 27 Cl 2 N 3 O 2 , and molecular weight is 448.39. The chemical structure is as follows:

formula

Aripiprazole tablets are available in 2 mg, 5 mg, 10 mg, 15 mg, 20 mg, and 30 mg strengths. Inactive ingredients include corn starch, FD&C Blue #2/Indigo Carmine Al, ferric oxide red, ferric oxide yellow, hydroxypropyl cellulose, lactose monohydrate, magnesium stearate and microcrystalline cellulose.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action


The mechanism of action of aripiprazole in schizophrenia is unknown. However, the efficacy of aripiprazole could be mediated through a combination of partial agonist activity at D 2 and 5-HT 1A receptors and antagonist activity at 5-HT 2A receptors. Actions at receptors other than D 2 , 5-HT 1A , and 5-HT 2A may explain some of the other clinical effects of aripiprazole (e.g., the orthostatic hypotension observed with aripiprazole may be explained by its antagonist activity at adrenergic alpha1 receptors).

12.2 Pharmacodynamics


Aripiprazole exhibits high affinity for dopamine D 2 and D 3 , serotonin 5-HT 1A and 5-HT 2A receptors (K i values of 0.34 nM, 0.8 nM, 1.7 nM, and 3.4 nM, respectively), moderate affinity for dopamine D 4 , serotonin 5-HT 2C and 5-HT 7 , alpha 1 -adrenergic and histamine H 1 receptors (K i values of 44 nM, 15 nM, 39 nM, 57 nM, and 61 nM, respectively), and moderate affinity for the serotonin reuptake site (K i =98 nM). Aripiprazole has no appreciable affinity for cholinergic muscarinic receptors (IC 50 >1000 nM). [Aripiprazole functions as a partial agonist at the dopamine D 2 and the serotonin 5-HT 1A receptors, and as an antagonist at serotonin 5-HT 2A receptor.]

12.3 Pharmacokinetics

Aripiprazole tablets activity is presumably primarily due to the parent drug, aripiprazole, and to a lesser extent, to its major metabolite, dehydro-aripiprazole, which has been shown to have affinities for D 2 receptors similar to the parent drug and represents 40% of the parent drug exposure in plasma. The mean elimination half-lives are about 75 hours and 94 hours for aripiprazole and dehydro-aripiprazole, respectively. Steady-state concentrations are attained within 14 days of dosing for both active moieties. Aripiprazole accumulation is predictable from single-dose pharmacokinetics. At steady-state, the pharmacokinetics of aripiprazole is dose-proportional. Elimination of aripiprazole is mainly through hepatic metabolism involving two P450 isozymes, CYP2D6 and CYP3A4. For CYP2D6 poor metabolizers, the mean elimination half-life for aripiprazole is about 146 hours.
ORAL ADMINISTRATION
Absorption
Tablet: Aripiprazole is well absorbed after administration of the tablet, with peak plasma concentrations occurring within 3 hours to 5 hours; the absolute oral bioavailability of the tablet formulation is 87%. Aripiprazole tablets can be administered with or without food. Administration of a 15 mg aripiprazole tablet with a standard high-fat meal did not significantly affect the C max or AUC of aripiprazole or its active metabolite, dehydro-¬aripiprazole, but delayed T max by 3 hours for aripiprazole and 12 hours for dehydro-aripiprazole.
Distribution
The steady-state volume of distribution of aripiprazole following intravenous administration is high (404 L or 4.9 L/kg), indicating extensive extravascular distribution. At therapeutic concentrations, aripiprazole and its major metabolite are greater than 99% bound to serum proteins, primarily to albumin. In healthy human volunteers administered 0.5 mg/day to 30 mg/day aripiprazole for 14 days, there was dose-dependent D 2 receptor occupancy indicating brain penetration of aripiprazole in humans.
Metabolism and Elimination
Aripiprazole is metabolized primarily by three biotransformation pathways: dehydrogenation, hydroxylation, and N-dealkylation. Based on in vitro studies, CYP3A4 and CYP2D6 enzymes are responsible for dehydrogenation and hydroxylation of aripiprazole, and N-dealkylation is catalyzed by CYP3A4. Aripiprazole is the predominant drug moiety in the systemic circulation. At steady-state, dehydro¬-aripiprazole, the active metabolite, represents about 40% of aripiprazole AUC in plasma.
Following a single oral dose of [ 14 C]-labeled aripiprazole, approximately 25% and 55% of the administered radioactivity was recovered in the urine and feces, respectively. Less than 1% of unchanged aripiprazole was excreted in the urine and approximately 18% of the oral dose was recovered unchanged in the feces.
Drug Interaction Studies
Effects of other drugs on the exposures of aripiprazole and dehydro-aripiprazole are summarized in Figure 1 and Figure 2, respectively. Based on simulation, a 4.5-fold increase in mean C max and AUC values at steady-state is expected when extensive metabolizers of CYP2D6 are administered with both strong CYP2D6 and CYP3A4 inhibitors. A 3-fold increase in mean C max and AUC values at steady-state is expected in poor metabolizers of CYP2D6 administered with strong CYP3A4 inhibitors.
Figure 1: The effects of other drugs on aripiprazole pharmacokinetics

Figure1
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Figure 2: The effects of other drugs on dehydro-aripiprazole pharmacokinetics

Figure2
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The effects of aripiprazole tablets on the exposures of other drugs are summarized in Figure 3.
Figure 3: The effects of aripiprazole on pharmacokinetics of other drugs

Figure3
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Studies in Specific Populations
Exposures of aripiprazole and dehydro-aripiprazole in specific populations are summarized in Figure 4 and Figure 5, respectively. In addition, in pediatric patients (10 to 17 years of age) administered with aripiprazole tablets (20 mg to 30 mg), the body weight corrected aripiprazole clearance was similar to the adults.
Figure 4: Effects of intrinsic factors on aripiprazole pharmacokinetics

Figure4
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Figure 5: Effects of intrinsic factors on dehydro-aripiprazole pharmacokinetics

Figure5
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