Promethazine
Phenergan
Phenothiazine antihistamine (H1) antiemetic + sedative
H1 antihistamine with anticholinergic + antidopaminergic activity → antiemetic + sedation + antihistamine effects.
Indications
- •PONV (rescue)
- •Motion sickness
- •Sedation/allergy
Dosing
| Context | Adult | Pediatric |
|---|---|---|
| PONV | 6.25–12.5 mg IV (low dose) or IM | — |
Pharmacokinetics
Onset ~5 min IV. Long duration 4–6 h. Hepatic.
Side effects
- !Sedation
- !SEVERE TISSUE INJURY/gangrene with IV extravasation or arterial injection (Black Box) — dilute + give slowly into a running line, or use IM
- !Extrapyramidal symptoms
- !Anticholinergic effects
- !Respiratory depression in young children (contraindicated <2 y)
Contraindications
- ×Children <2 years (fatal respiratory depression)
- ×Intra-arterial/subcutaneous injection
Clinical pearls
- ★BLACK BOX: severe tissue necrosis with extravasation/intra-arterial injection — dilute, give slowly into a free-flowing IV, prefer deep IM.
- ★Contraindicated in children <2 (respiratory depression).
Other drugs in Antiemetics & Related
- Ondansetron
Blocks serotonin receptors at vagal afferents and chemoreceptor trigger zone.
- Metoclopramide
Central D2 antagonism at the chemoreceptor trigger zone (antiemetic). Peripherally, sensitizes upper-GI tissue to acetylcholine → increases lower esophageal sphincter tone, accelerates gastric emptying, speeds duodenal transit. Mild 5-HT4 agonism contributes to prokinesis.
- Droperidol
Potent central D2 antagonism at the chemoreceptor trigger zone. Also α-adrenergic blockade and mild GABA-A facilitation. Highly effective antiemetic and sedative — historically a key component of neuroleptanalgesia.
- Aprepitant
Selective antagonist at central neurokinin-1 receptors in the area postrema and nucleus tractus solitarius. Blocks substance-P-mediated emesis, particularly the delayed phase (24–72 h post-stimulus) where 5-HT3 antagonists lose efficacy.
- Granisetron
Blocks serotonin 5-HT3 receptors (central CTZ + peripheral vagal afferents). More selective + longer-acting than ondansetron.
- Dolasetron
5-HT3 antagonist (prodrug → hydrodolasetron). Effective antiemetic but the most QT/dysrhythmia-prone of the class.
- Haloperidol
Dopamine D2 antagonist (CTZ) → antiemetic at low doses; antipsychotic/sedating at higher doses.
Browse all classes: /reference/drugs
Suggested reading
- •Stoelting & Hines, Pharmacology & Physiology in Anesthetic Practice, 6e
- •Miller's Anesthesia, 9e
- •FDA package insert
