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Promethazine (Phenergan)

Promethazine (Phenergan) is an H1 receptor antagonist, and a weak dopamine antagonist that competes with histamine-1 and dopamine-2 receptors in the chemoreceptor trigger zone of the brain to decrease nausea, vomiting, and motion sickness. Side effects include respiratory depression, sedation, dry mouth, urinary retention, and extrapyramidal symptoms, such as dystonia, akathisia, and parkinsonism. This medication should not be given to children under the age of two, due to increased risk of death, related to severe respiratory depression. Keep in mind, if promethazine must be given intravenously, it should be administered through a large bore IV with a flow rate to prevent tissue necrosis. Extravasation can lead to serious complications, such as abscess formation and gangrene that requires amputation.
Histamine H1 Receptor Antagonist
History-man with (1) Wand in Ant-toga

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.

Weak Dopamine Antagonist
Weak Doberman in Ant-toga

Promethazine also functions as a weak dopamine antagonist, blocking dopamine-2 receptors in the chemoreceptor trigger zone, thus decreasing nausea and vomiting.

Nausea and Vomiting

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

Motion Sickness

Promethazine may also be prescribed to treat motion sickness.

Respiratory Depression
Deflated Lungs

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.

Anticholinergic Effects

Patients may also experience anticholinergic effects, such as dry mouth and urinary retention. The patient should be encouraged to void before taking this medication.

Extrapyramidal Symptoms

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

Use Large Bore IV
Large Bore IV

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.

Monitor for Tissue Necrosis
Monitor Tissue-box Necrosis-crow

When given via IV push, patients receiving promethazine should be closely monitored for signs of tissue necrosis.

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