Extrapyramidal symptoms, antipsychotic agents causing

Most antipsychotics and especially the piperazines and the butyrophenones can cause extrapyra-midal symptoms. Blockade of dopamine receptors mainly in the corpus striatum is held responsible for these extrapyramidal effects. They may become manifest as a variety of clinical symptoms and it should be noted that within 24 8 hours after the beginning of treatment acute dystonic reactions like torticollis, facial grimacing and opisthotonos may occur. Parkinsonism-like symptoms such as bradyki-nesia, rigidity and tremor occur after weeks or months of therapy and are more common in the elderly. Motor restlessness, i.e. akathisia, also mostly occurs not before weeks or months after starting therapy. The tendency of an antipsychotic agent to produce extrapyramidal symptoms appears to be inversely related to its ability to block cholinergic receptors. 

FIGURE 11 — 11. One compensation for the overactivity of acetylcholine that occurs when dopamine receptors are blocked is to block the acetylcholine receptors with an anticholinergic agent. Thus, anticholinergics overcome excess acetylcholine activity caused by removal of dopamine inhibition when dopamine receptors are blocked by conventional antipsychotics. This also means that extrapyramidal symptoms (EPS) are reduced. 

The belladonna alkaloids and related muscarinic receptor antagonists have long been used in parkinsonism. These agents can be effective adjuncts to treatment with levodopa see Chapter 20). Muscarinic receptor antagonists also are used to treat the extrapyramidal symptoms that commonly occur as side effects of conventional antipsychotic drug therapy see Chapter 18). Certain antipsychotic drugs are relatively potent muscarinic receptor antagonists, and these cause fewer extrapyramidal side effects. 

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