Antipsychotic drug overdose.

EMERGENCY nurse 17 Antipsychotic drugs (or neuroleptics) are a large class of drugs which can be divided into three groups: phenothiazine, miscellaneous and atypical (Box 1). They are used to tranquillise patients without impairing consciousness and without causing paradoxical excitement. They are often referred to as major tranquillisers but this is misleading since these drugs also relieve florid psychotic symptoms such as thought disorder, hallucinations and delusions, and prevent relapse. Typical antipsychotic drugs work by blocking post-synaptic dopamine D2 receptors in the brain. They vary in potency, the greater the potency the greater the affinity for the D2 receptors. Low potency drugs, such as chlorpromazine which are given in higher doses, are generally less selective and thus are capable of producing more adverse effects at therapeutic doses because of interaction with other receptors. In contrast, high potency drugs, such as haloperidol, are more selective. Their adverse effects are generally due to dopamine blockade rather than clinical antipsychotic drugs