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administration [227].   More recently, aripiprazole, a quinolinone derivative, has received considerable attention [228]. Aripiprazole is a partial dopamine agonist with a high affinity for D2 and D3 receptors and with a moderate affinity for 5HT1A, 5HT2A and histamine-1 receptors.  Experimental studies have shown that it has low intrinsic activity, or partial agonist/antagonist activity, at dopamine receptors. There is also experimental evidence that aripiprazole acts as a full agonist at dopamine autoreceptors, but acts as a relative antagonist at post-synaptic receptors.  Its long half-life (60 h), preliminary clinical evidence of its antipsychotic efficacy, its low cardiotoxicity and its favourable safety profile [229,231] indicate that this approach to the development of novel antipsychotic medications opens up new possibilities for the future.

Iloperidone is a new antipsychotic drug currently undergoing clinical development. In radioligand studies, iloperidone shows a high affinity for D2 and D4 receptors and, to a lesser extent,  D1 and D2 receptors.    In addition, it shows a very high affinity for 5HT2A receptors and to a lesser extent,  5HT1A, 5HT1B, 5HT2C and 5HT6 receptors.  The most unique pharmacological aspect of iloperidone is its very high affinity for alpha-2 adrenoreceptors.  This effect might contribute to the increased release of adrenaline and dopamine from the prefrontal cortex; clozapine has a somewhat similar effect.  Results from a randomized, double-blind, multicenter study show that iloperidone has an efficacy comparable to that of haloperidol but with fewer EPSs and no elevation of prolactin.

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