Evidence-Based Reviews

New Investigators: What makes aripiprazole the ‘different’ antipsychotic

Current Psychiatry. 2005 July;4(7):51-60

Off-label use of ‘dopamine stabilizer’ requires caution.

References

1. Kane JM, Carson WH, Saha AR, et al. Efficacy and safety of aripiprazole and haloperidol versus placebo in patients with schizophrenia and schizoaffective disorder. J Clin Psychiatry 2002;63:763-71.

2. Marder SR, McQuade RD, Stock E, et al. Aripiprazole in the treatment of schizophrenia: safety and tolerability in short-term, placebo-controlled trials. Schizophr Res 2003;61:123-36.

3. Keck PE, Jr, Marcus R, Tourkodimitris S, et al. A placebo-controlled, double-blind study of the efficacy and safety of aripiprazole in patients with acute bipolar mania. Am J Psychiatry 2003;160:1651-8.

4. Potkin SG, Saha AR, Kujawa MJ, et al. Aripiprazole, an antipsychotic with a novel mechanism of action, and risperidone vs placebo in patients with schizophrenia and schizoaffective disorder. Arch Gen Psychiatry 2003;60:681-90.

5. Grady MA, Gasperoni TL, Kirkpatrick P. Aripiprazole. Nat Rev Drug Discov 2003;2:427-8.

6. Stigler KA, Posey DJ, McDougle CJ. Aripiprazole for maladaptive behavior in pervasive developmental disorders. J Child Adolesc Psychopharmacol 2004;14:455-63.

7. Tamminga CA. Partial dopamine agonists in the treatment of psychosis. J Neural Transm 2002;109:411-20.

8. Arciniegas DB, Beresford TP. Neuropsychiatry: an Introductory Approach .Cambridge, UK: Cambridge University Press; 2001.

9. Stahl SM. Psychopharmacology of Antipsychotics .London: Martin Dunitz Ltd.; 1999.

10. Tamminga CA, Gotts MD, Thaker GK, et al. Dopamine agonist treatment of schizophrenia with N-propylnorapomorphine. Arch Gen Psychiatry 1986;43:398-402.

11. Grunder G, Carlsson A, Wong D. Mechanism of new antipsychotic medications: occupancy is not just antagonism. Arch Gen Psychiatry 2003;60:974-7.

12. Burris K, Molski T, Xu C, et al. Aripiprazole, a novel antipsychotic, is a high-affinity partial agonist at human dopamine D2 receptors. J Pharmacol Exp Ther 2002;302:381-9.

13. Lieberman J. Dopamine partial agonists: a new class of antipsychotic. CNS Drugs 2004;18:251-67.

14. Yokoi F, Grunder G, Biziere K, et al. Dopamine D2 and D3 receptor occupancy in normal humans treated with the antipsychotic drug aripiprazole (OPC 14597): a study using positron emission tomography and [11C]raclopride. Neuropsychopharmacology 2002;27:248-59.

15. Kapur S, Zipursky R, Jones C, et al. Relationship between dopamine D(2) occupancy, clinical response, and side effects: a double-blind PET study of first-episode schizophrenia. Am J Psychiatry 2000;157:514-20.

16. U.S. Food and Drug Administration. Medwatch online. Available at: http://www.fda.gov/medwatch/SAFETY/2004/abilify_pi.pdf. Accessed June 7, 2004.

17. Pigott T, Carson W, Saha A, et al. Aripiprazole for the prevention of relapse in stabilized patients with chronic schizophrenia: a placebo-controlled 26-week study. J Clin Psychiatry 2003;64:1048-56.

18. Mallikaarjun S, Salazar D, Bramer S. Pharmacokinetics, tolerability, and safety of aripiprazole following multiple oral dosing in normal healthy volunteers. J Clin Pharmacol 2004;44:179-87.

19. Casey D, Carson W, Saha A, et al. Switching patients to aripiprazole from other antipsychotic agents: a multicenter randomized study. Psychopharmacology 2003;166:391-9.

20. Nakai S, Hirose T, Uwahodo Y, et al. Diminished catalepsy and dopamine metabolism distinguish aripiprazole from haloperidol or risperidone. Eur J Pharmacol 2003;472:89-97.

21. Sajbel T, Cheney E, DeQuardo J. Aripiprazole-associated dyskinesia. Ann Pharmacother 2005;39:200-1.

22. Reeves R, Mack J. Worsening schizoaffective disorder with aripiprazole. Am J Psychiatry 2004;161:1308.-

23. Ramaswamy S, Vijay D, William M, et al. Aripiprazole possibly worsens psychosis. Int Clin Psychopharmacol 2004;19:45-8.

24. Mendhekar D. Aripiprazole-induced rabbit syndrome. Aust N Z J Psychiatry 2004;38:561.-

25. Lindsey R, Kaplan D, Koliatsos V, et al. Aripiprazole and extrapyramidal symptoms. J Am Acad Child Adolesc Psychiatry 2003;42:1268-9.

26. Davenport J, McCarthy M, Buck M. Excessive somnolence from aripiprazole in a child. Pharmacotherapy 2004;24:522-5.

27. DeQuardo J. Worsened agitation with aripiprazole: adverse effect of dopamine partial agonism? J Clin Psychiatry 2004;65:132-3.

28. Cohen S, Rulf D, Pies R. Extrapyramidal side effects associated with aripiprazole coprescription in 2 patients. J Clin Psychiatry 2005;66:135-6.

Aripiprazole, the first FDA-approved partial dopamine agonist, causes few side effects when used to treat schizophrenia or acute bipolar mania. This relatively safe profile in approved uses has led clinicians to try aripiprazole for off-label uses as well, though evidence of the drug’s efficacy and safety in other psychiatric conditions is limited (Box 1).^1-7 Because this practice may involve unknown risks, this article:

reviews aripiprazole’s role in correcting dopaminergic dysfunction in patients with schizophrenia
cites adverse effects reported with aripiprazole use and discusses concerns about its off-label use.

Box 1

Off-label aripiprazole: The unknowns

Aripiprazole shows clear efficacy for treating acute mania and schizophrenia’s negative and positive symptoms, but its effectiveness and safety in other psychiatric illnesses is unknown. Even so, it is being used to treat psychotic unipolar and bipolar depression, attention-deficit/hyperactivity disorder, oppositional defiant disorder, and pervasive developmental disorders in childrenand adults.

Dopamine differences. Do not assume that aripiprazole’s safety and effectiveness in treating schizophrenia translates to other psychiatric conditions. Dopamine dysfunction patterns differ in persons with and without schizophrenia; therefore, aripiprazole’s regional and functional selectivity at dopamine receptors—and treatment response and tolerability—is also likely to differ.

Antipsychotic differences. Aripiprazole is unlike other psychotropics and cannot be assumed to have similar therapeutic effects. The agent’s dopamine agonist and antagonist properties hinge on regional dopamine concentrations as well as the drug itself.

Dopaminergic risks in combination. Numerous drugs modulate dopamine function, and switching and combining drugs places patients at unknown risk of dopaminergic side effects with aripiprazole. Adding an antagonist or a low-dose antagonist combination with aripiprazole may increase competition for dopamine receptors and modify its intrinsic activity, depending on the antagonist dosage and regional dopamine concentrations.

Source: References 1-7

DOPAMINE AND SCHIZOPHRENIA

Dopamine neurons arise from two major nuclei in the mesencephalon (midbrain): the substantia nigra and ventral tegmental area (VTA). Neurons from the substantia nigra extend to the basal ganglia via the mesostriatal (nigrostriatal) pathway, which influences extrapyramidal motor function. The VTA sends dopaminergic neurons through mesolimbic and mesocortical pathways.

The basic limbic system includes the cingulate and orbitofrontal gyri, hippocampus, hypothalamus, thalamus, amygdala, medial temporal cortex, and the periaqueductal gray. This system controls emotion, episodic memory, pain, and primitive behaviors such as eating, fighting, sexual desire, and grooming.⁸ The limbic system is surrounded by cortex, where higher-order sensory, cognitive, and motor processes occur. The VTA links limbic and cortical functions via dopamine.

The tuberoinfundibular pathway, another clinically important dopaminergic route, projects from the hypothalamus to the anterior pituitary gland and regulates prolactin secretion.

Functional dopamine neurotransmission abnormalities in schizophrenia are generally characterized by region, with:

excessive mesolimbic pathway activity resulting in positive symptoms such as delusions and hallucinations
mesocortical projection deficits resulting in cognitive and negative symptoms such as impaired memory and attention, emotional blunting, alogia, avolition, and anhedonia.

Dopamine function abnormalities in schizophrenia occur in:

projections from the substantia nigra to the caudate and putamen in the basal ganglia
mesolimbic connections to the anterior cingulate, hippocampus, and parahippocampus
mesocortical projections to the prefrontal cortex.

These dysfunctions contribute to abnormal motor function, perception, attention, memory, volition, emotion, and executive function.⁹

WHY ARIPIPRAZOLE WAS CREATED

Differences in regional dopamine function and observations of dopamine agonists’ therapeutic effects in schizophrenia¹⁰ led to development of partial dopamine agonists such as aripiprazole (Box 2).^11,12

Aripiprazole and the investigational agent bifeprunox have complex pharmacologic actions involving numerous neurotransmitters—dopamine, serotonin, and histamine—but are believed to be principally partial agonists at pre- and postsynaptic dopamine receptors. Specifically, aripiprazole decreases hyperdopaminergic states while preserving dopamine function by partial agonism and decreased stimulation of presynaptic regulatory autoreceptors.⁵

The FDA approved aripiprazole for treating schizophrenia in 2002 and acute bipolar mania in 2004. A dihydroquinolone unrelated to other antipsychotics, it has an active partial agonist metabolite (dehydro-aripiprazole), high affinity for D2 receptors (Figure 1), and partial agonism at dopamine and serotonin receptors.¹³

Phase III trials are in progress for bifeprunox, a partial dopamine agonist/antagonist and serotonin receptor agonist being investigated for schizophrenia. An FDA decision on its approvability is expected in 2007.

Aripiprazole has approximately 30% intrinsic dopaminergic activity, estimated from studies showing a low incidence of extrapyramidal symptoms (EPS) with dosages up to 30 mg and PET studies showing a therapeutic range of postsynaptic D2 receptor occupancy of 80% to 95%.¹⁴ This small intrinsic activity limits excessive stimulation and dopamine receptor blockade.¹¹ It also limits down-regulation of regulatory dopamine autoreceptors and preserves dopaminergic function in pre- and postsynaptic neurons.

The therapeutic window for dopamine receptor agonists (DA) and serotonin-dopamine receptor agonists (SDA) used in schizophrenia is 60% to 80% D2 receptor occupancy in mesostriatal neurons. D2 receptor occupancy and antagonism >80% significantly increases risk of EPS.¹⁵ Excessive dosing of high-potency antipsychotics with strong postsynaptic dopamine receptor affinity carries the highest risk of hypodopaminergic side effects, such as cognitive impairment, worsening of negative symptoms, akathisia, Parkinsonism, and hyperprolactinemia.