Promethazine Mechanism of Action for Nursing

Promethazine competes with histamine at histamine-1 receptor sites throughout the body. The medication’s antiemetic property is likely related to its effect in the chemoreceptor trigger zone of the brain. Assess for orthostatic hypotension.

Promethazine also functions as a weak dopamine antagonist, blocking dopamine-2 receptors in the chemoreceptor trigger zone, thus decreasing nausea and vomiting. Be sure to assess for neuroleptic malignant syndrome (NMS) due to this medication's dopamine antagonist properties.

This medication is indicated in the treatment of nausea and vomiting related to chemotherapy and surgical procedures.

Promethazine may also be prescribed to treat motion sickness.

This medication can cause severe respiratory depression and should not be used in children under the age of two.

Sedation, CNS depression, and fatigue are side effects associated with promethazine. Patients should be advised to avoid hazardous activities, such as driving while taking this medication. Effects may be potentiated when used with other sedative drugs or ethanol. Use with caution in disorders where CNS depression is a feature

Patients may also experience anticholinergic effects, such as constipation, xerostomia, blurred vision, urinary retention The patient should be encouraged to void before taking this medication. They should be used with caution in patients with decreased gastrointestinal motility, urinary retention, BPH, xerostomia, or visual problems.

Movement disorders or extrapyramidal effects can be induced by promethazine. Patients may develop muscle spasms or contractions, restlessness, bradykinesia, and tremor.

If extravasation occurs during intravenous administration, promethazine can cause tissue death and abscess formation. To ensure patient safety, this medication should be administered through a large bore IV, at a rate of no more than 25 mg/min. Patients should be encouraged to report pain or burning during IV administration.

When given via IV push, patients receiving promethazine should be closely monitored for signs of tissue necrosis. This is because this medication is also toxic to the innermost coating of blood vessels and surrounding connective tissue.