Atypical antipsychotic drugs: beyond acute psychosis, new directions

Translating knowledge of genetics and pharmacology into improving everyday practice

Bipolar disorder is associated with significant morbidity and mortality; however, many aspects of this disorder remain poorly understood. It is likely that rapid advances in molecular genetics and neuroimaging will play a major role in advancing our understanding of bipolar disorder in future. Molecular genetics studies have already identified some candidate genes; for example, the BDNF, G72 and XBP1 genes, and chromosomal 'hot spots', which may confer a predisposition to development of bipolar disorder. Such advances may facilitate earlier, easier and more accurate diagnosis and provide novel targets for the treatment of this condition. Brain imaging studies using positron emission tomography and single photon emission computed tomography have shown that reduction in brain 5-hydroxytryptamine type 2 (5-HT(2)) receptors may be associated with prevention of or relief from depressive symptoms. Similarly, other imaging studies suggest that increased dopamine levels in the synapse mediate the symptoms of bipolar mania and that reduction in dopamine transmission through reduction in dopamine synthesis or blockade of dopamine D(2) receptors may be associated with antimanic effects. The ability of atypical antipsychotics to block both 5-HT(2) and D(2) receptors and downregulate 5-HT(2) receptors may explain how these drugs treat both the depressive and manic symptoms of bipolar disorder. Although molecular genetics and imaging techniques are not yet used as clinical tools for bipolar disorder, they provide valuable data to improve the understanding of the pathophysiology of bipolar disorder and should lead to new treatments and potentially episode prevention.

Manic symptoms associated with quetiapine treatment

This case illustrates the induction of manic-like symptoms in a 26-year-old male patient with DSM-IV paranoid schizophrenia following treatment with quetiapine. The only drug he had received prior to quetiapine was risperidone which was occasionally taken in the previous 3 years. The manic symptoms remitted after quetiapine withdrawal.

Real-time analysis of dopamine: antagonist interactions at recombinant human D2long receptor upon modulation of its activation state

1. Antipsychotic drugs may mediate their therapeutic effects not only by preventing the binding of dopamine but also by decreasing the propensity of the dopamine receptor to assume an active R* state. Ligand-mediated activation and blockade of the recombinant human D(2long) receptor was investigated in CHO-K1 cells upon modulation of its R* state. 2. Both the Ala(371)Lys (A371K) and Thr(372)Arg (T372R) D2long receptor mutants could be activated in a ligand-dependent manner via a chimeric G(alphaq/o) protein, and more efficaciously so than with the promiscuous G(alpha15) protein. 3. Dopamine and partial agonists (E(max): lisuride >> (+)-UH 232 approximately bromerguride) displayed dissimilar Ca(2+) kinetic properties at wild-type and mutant receptors. A371K and T372R D2long receptor mutants demonstrated an attenuated and enhanced maximal response to these partial agonists, respectively. 4. Dopamine antagonists were unable to block the transient high-magnitude Ca(2+) phase at the wild-type D2long receptor upon simultaneous exposure to antagonist and dopamine, while full blockade of the low-magnitude Ca(2+) phase did occur at a later time (onset-time: haloperidol < bromerguride < (+)-butaclamol). A similar, though more efficacious, antagonist profile was also found at the A371K mutant receptor. Conversely, the blockade of the low-magnitude Ca(2+) phase was attenuated (haloperidol) or almost absent [(+)-butaclamol and bromerguride] at the T372R mutant receptor. 5. In conclusion, mutagenesis of the Ala(371) and Thr(372) positions affects in an opposite way the ligand-dependent activation and blockade of the D2long receptor. The observed attenuation of dopamine-mediated Ca(2+) signal generation with different decay-times may underlie distinct properties of the dopaminergic ligands.

An assessment of iloperidone for the treatment of schizophrenia

Iloperidone (Novartis' Zomariltrade mark) is an atypical antipsychotic agent for the treatment of schizophrenia. Current trends in the treatment of schizophrenia indicate that some atypical antipsychotics are being recommended as first-line therapy. Atypical antipsychotics, in addition to being dopamine (D) receptor antagonists, are all relatively potent serotonin (5-HT) receptor antagonists and are less likely than conventional dopamine antagonists to induce movement disorders. However, all of these agents differ in their receptor profiles and clinical profiles. Iloperidone, a benzisoxazole, is a mixed 5-HT(2A)/D(2)antagonist. Iloperidone was found to be more potent than its analogues when compared with haloperidol in antagonising climbing behaviour in mice. Iloperidone is extensively metabolised and the main circulating metabolite is reduced iloperidone. In patients treated with iloperidone, a low incidence of extrapyramidal symptoms and weight gain has been shown. Data from Phase II trials demonstrated efficacy in patients at doses of 8 mg/day and tolerability was good up to 32 mg/day. Phase III prospective, double-blind, randomised trials with iloperidone are in progress under the ZEUS (Zomariltrade mark Efficacy Utility and Safety) programme involving 3300 patients. Iloperidone, with a balance of activity at the dopaminergic and serotonergic receptors, has obvious advantages over clozapine and olanzapine, both of which have a similar receptor profile as they favour serotonergic over dopamine receptors. Iloperidone is likely to reach the market in 2001 and has favourable prospects in the atypical antipsychotic market for schizophrenia, which is expanding from US$ 1.5 billion in 2000 to US$ 3 billion in 2005.