There are important differences between atypical antipsychotics in the relative risk of adverse effects
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There are important differences between atypical antipsychotics in the relative risk of adverse effects M1 D1 D 2
D1
α1
D1 D2
H1
5-HT2A
5-HT2A 5-HT1A α1
5-HT2A α2 D2 Haloperidol D1
5-HT1A
α1
H1
Clozapine α1 D2
D2 5-HT2A
5-HT1A
α1 M1
H1 Olanzapine
α2
Quetiapine
D1
α 2 H1 D2 α1
5-HT2A
5-HT2A Ziprasidone
Risperidone
Fig. 1. Comparison of antipsychotic receptor binding profiles between haloperidol and the atypical antipsychotics clozapine, quetiapine, olanzapine, ziprasidone and risperidone.[2] 5-HT = serotonin; α = α-adrenergic; D = dopamine; H = histamine; M = muscarinic.
Atypical antipsychotic agents are associated with fewer extrapyramidal symptoms than conventional antipsychotic drugs. They may, however, cause a variety of other adverse effects, including hyperprolactinaemia, weight gain, hyperglycaemia and postural hypotension. Careful patient monitoring allows for early detection and treatment of adverse symptoms.
Adverse effects related to receptor binding Adverse effects of pharmaceutical agents can impair health-related quality of life, result in morbidity and mortality, and contribute to poor adherence with medication.[1] Antipsychotic agents, used to treat schizophrenia and other major psychiatric disorders, exert their effects primarily by acting on the dopamine D2 receptors in the brain.[2] The receptor-binding profile of each atypical antipsychotic agent (figure 1) is related to its adverse effects and adverse drug reactions. Although there are methodological problems in the assessment and relative interpretation of tolerability data between agents, due to a lack of head-to-head comparative and inconsistent reporting of tolerability, the relative risk of a number of adverse effects differs not only between conventional and atypical antipsychotics, but also between atypical antipsychotics[1,2] (table I).
Cause few extrapyramidal symptoms Conventional antipsychotic agents bind more tightly than dopamine to the D2 receptor,[2] resulting in extrapyramidal symptoms (EPS) [such as parkinsonism, acute dystonia, akathisia and tardive dyskinesia] in as many as 75% of patients.[3] Atypical antipsychotics bind more loosely than dopamine to the D2 receptor and then dissociate rapidly, thereby reducing the incidence of EPS seen with conventional antipsychotic therapy.[2] This effect is enhanced by the drugs’ blockage of 5-HT2A receptors, which balances the actions of dopamine and serotonin.[4] Notably, the additional action of atypical antipsychotics on 5-HT receptors account for their improved efficacy on the negative symptoms of schizophrenia relative to conventional antipsychotics.[5] While the risk of EPS is generally decreased with the use of atypical antipsychotics compared with conventional antipsychotics, the relative risk of EPS varies between different atypical antipsychotics (table I), is greater with higher dosages (especially of risperidone) and in older patients, and is lowest with quetiapine and clozapine.[1] Atypical antipsychotics are associated with a variety of other adver
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