Pediatric emergency medicine trisk 3083 3083
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Phenothiazine toxicity may include CNS depression, hypotension, and
extrapyramidal side effects, including dystonia. All but dystonia are dose
dependent.
Current Evidence. The phenothiazines are commonly prescribed major
tranquilizers. Phenothiazines are also often used to treat nausea and vomiting in
young children. The toxic effects of this drug class primarily involve the three
components of the nervous system: central, autonomic, and extrapyramidal.
The three subgroups of phenothiazines—aliphatic, piperazine, and piperidine—
vary in their effects on the different components of the CNS. In general, the
aliphatic group (e.g., chlorpromazine) may cause sedation and hypotension in
overdose. The piperazine group (e.g., prochlorperazine) is more likely to create
extrapyramidal side effects. Several new classes of nonphenothiazine
antipsychotic agents are now widely prescribed.
Clinical Considerations. The manifestations of phenothiazine toxicity may be
dose dependent or dose independent (i.e., idiosyncratic). These have significantly
different features.
With dose-dependent effects, the manifestations of intoxication after acute
ingestion vary from mild to severe. Mild intoxication causes CNS signs such as
sedation, ataxia, and slurred speech. The anticholinergic effects of these drugs
may cause constipation, urinary retention, and blurred vision. Because
phenothiazines have potent actions on the temperature-regulating center of the
hypothalamus, temperature disturbances occur in up to 30% of patients and may
consist of hypothermia or hyperthermia. Orthostatic hypotension, the probable
result of peripheral vasodilation, may also be noted with mild intoxication.
Moderate intoxication may cause significant depression in the level of
consciousness. Extrapyramidal effects are notable, with muscle stiffness or
cogwheel rigidity seen on passive movement of the neck, biceps, or quadriceps.
Anticholinergic manifestations are severe and include acute urinary retention and
paralytic ileus; hypotension may be profound. Cardiac conduction disturbances
may make their appearance and are often heralded by a prolonged QT interval.
In severe overdoses patients are unarousable. Deep tendon reflexes may be
hyperactive. Dystonic reactions may occur, involving the head and neck and the
cranial nerves (torticollis and opisthotonos). Arrhythmias and shock may result in
death.
The dose-independent effect of the phenothiazines is the dystonic reaction.
This striking clinical occurrence consists of episodic spasm of voluntary muscles,
