Promethazine
- Class: Antiemetic / antihistamine
- Used for: nausea
- Say it: proh-METH-uh-zeen
- Forms: tablet, oral liquid, suppository, injection
PROMETHAZINE settles the nausea — but it burns like PROMETHEUS' FIRE if it leaks out of the vein.
The tissue toxicity is the thing to remember: extravasation or arterial injection causes necrosis, and has led to amputation. Many hospitals have removed the intravenous route entirely.
It blocks H1, muscarinic, dopamine D2 and alpha-1 receptors. That untidiness is why it treats nausea, allergy and insomnia at once — and why it sedates so heavily.
Side effects
Common: drowsiness, dry mouth, dizziness
Serious: tissue injury if injected, breathing depression in young children
Typical dose
12.5–25 mg every 4–6 hours
Never under age two. Avoid the intravenous route where possible — extravasation causes necrosis.
Check yourself
What is the main danger of intravenous promethazine?
- Severe tissue necrosis if it leaks from the vein or enters an artery
- It cannot be given with any other antiemetic
- It raises blood pressure sharply
- It is ineffective by the intravenous route
Show answer
A. Severe tissue necrosis if it leaks from the vein or enters an artery
The problem is local and physical rather than systemic. Promethazine is intensely irritant, and injuries from extravasation have been serious enough that many institutions now restrict it to the oral or rectal route.
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