Extrapyramidal Reactions

Two extrapyramidal conditions, acute dystonia and akathisia, occur early during treatment, while parkinson-ism tends to evolve gradually over days to weeks. All three reactions occur most commonly with the high-potency antipsychotics (Table 34.1) and are related to high D2-receptor occupancy. Acute dystonia, which occurs in about 5% of patients on antipsychotic therapy, consists of uncontrollable movements and distortions of the face, head, and neck. It can be treated with centrally acting an-timuscarinic agents, such as benztropine, while antipsy-chotic therapy is temporarily discontinued. When this reaction subsides, the anticholinergic can be withdrawn.

The incidence of akathisia is about 20%; the syndrome consists of intense motor restlessness and agitation that contribute to a behavioral deterioration. It is frequently unresponsive to anticholinergics and is more effectively treated with benzodiazepines and (3-adrenergic antagonists, such as propranolol.

Signs of parkinsonism—akinesia, tremor, rigidity— can develop gradually, but this reaction usually responds favorably to central antimuscarinic agents. As with dystonia, parkinsonism may subside, permitting withdrawal of the antimuscarinic drug.

TABLE 34.2 Significant Adverse Effects of Antipsychotic Drugs

Type

Manifestations

Mechanism

Sedation

Drowsiness, lethargy

(^-adrenoceptor block, Hj histamine receptor block

Extrapyramidal reactions

Dystonias, akathisia, parkinsonism

D2-receptor block

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