A clinical guide to antipsychotic drugs.

Antipsychotic medications have altered the treatment of psychosis. The effect of typical agents is presumed to be associated with dopamine D2-receptor blockade. Response to these drugs can be evaluated by measuring target symptoms. Behavioural symptoms are generally first to respond, followed by affective symptoms, and then symptoms of disturbed cognition and perception. Predictors of response include age of onset, premorbid function, family history, cognitive function, ventricle size, and levels of homovanillic acid. As all conventional antipsychotic medications of comparable dose are generally of equivalent efficacy (with the exception of clozapine), choice is based on past response and the patient's tolerance of adverse effects. When antipsychotic agents are administered in the short term to control agitated dangerous behaviour, they can be given intramuscularly and augmented with benzodiazepines. For the ongoing treatment of psychosis, haloperidol 5 mg/day, or its equivalent, is usually sufficient. Continuation of treatment after an acute episode may be decided on the basis of chronicity of the psychotic illness. Relapse rates are higher when patients do not continue to receive medication. Lower maintenance doses may result in higher relapse rates but fewer adverse effects. Long-acting intramuscular depot preparations may be used to aid compliance in long term therapy. Adverse reactions correlate with potency. High potency drugs (i.e. those with greater D2 postsynaptic receptor affinity) are generally associated with extrapyramidal symptoms, including acute dystonic reactions, akathisia, tardive dyskinesia and Parkinsonism. Neuroleptic malignant syndrome is associated with all neuroleptic drugs. Low potency agents may cause orthostatic hypotension, sedation and anticholinergic effects. Clozapine has been shown to be effective in 30 to 40% of patients resistant to previous treatment. It does not cause extrapyramidal symptoms, but does have side effects similar to those of low potency agents and may cause agranulocytosis; it is therefore reserved for those patients who have not responded to therapy with 2 other agents. Several other atypical drugs are currently being investigated.