Phenothiazines

Phenothiazine compounds are clinically useful antipsychotic and antiemetic medications.

Phenothiazine antihistamines such as promethazine (phenergan) and prochlorperazine (compazine) are highly effective antiemetics.

Phenothiazine neuroleptics such as chlorpromazine (thorazine) are used in the treatment of schizophrenia and psychosis.

Chlorpromazine can also effectively treat uncontrollable hiccups and acute migraine headaches.

Common side effects of sedation and delirium may be particularly notable in the postop period and in susceptible pts.

Severe extrapyramidal symptoms may arise from antidopaminergic activity.

Tardive dyskinesia may result from long-term use and may be irreversible.

Contraindicated in Parkinson disease; may worsen tremor and Parkinsonism.

Autonomic dysfunction may result from sympatholytic and anticholinergic effects.

Cardiac conduction defects and arrhythmias may occur with acute or chronic dosing, most commonly manifesting as a long QT interval.

Accidental arterial injection or venous extravasation of promethazine can cause tissue necrosis.

Neuroleptic malignant syndrome is a potentially fatal reaction to phenothiazines involving hyperthermia, rhabdomyolysis, tachycardia, and arrhythmias.

Phenothiazines undergo hepatic metabolism; use caution in pts with hepatic dysfunction.

Inactive metabolites excreted in bile/urine; pharmacokinetics rarely affected by renal failure.

Phenothiazines are highly protein-bound (>90%).

Prochlorperazine and promethazine have clinical half-lives of approximately 4–8 h after IV administration.