Promethazine (Phenergan) is an oral, intramuscular (IM), rectal, and intravenous (albeit with caution!) phenothiazine derivative that is both a first-generation antihistamine (H1 receptor antagonism) and a weak typical antipsychotic (D2 receptor antagonism). It also demonstrates antagonism of muscarinic acetylcholine receptors (anticholinergic) and NMDA receptors (similar to ketamine), conferring some degree of analgesia too.

Given its broad receptor antagonism profile, promethazine is useful for allergies, motion sickness, to provide sedation, and what I use it for the most as a cardiac anesthesiologist and intensivist – an antiemetic. While medications like ondansetron (Zofran) are good PROPHYLACTIC agents, promethazine is a better option if a patient is already nauseous.

Side effects include respiratory depression, acute dystonia/tardive dyskinesia, confusion, dizziness, NMS, and rarely hypotension, bone marrow suppression, and seizures. If given IV, extravasation can cause irreversible tissue damage, so careful administration and monitoring is essential! 

Drop me a comment below with your experiences regarding promethazine!

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