Metoclopramide
Reglan
Dopamine D2 receptor antagonist (prokinetic)
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.
Indications
- •Aspiration prophylaxis in full-stomach / OB / GERD patients (paired with H2 blocker + non-particulate antacid)
- •PONV (modest efficacy; reserve when other agents not preferred)
- •Diabetic gastroparesis
- •Migraine adjunct
Dosing
| Context | Adult | Pediatric |
|---|---|---|
| Aspiration prophylaxis preop | 10 mg IV 30–60 min before induction | — |
| PONV | 10 mg IV (modest evidence; not first-line) | — |
| Gastroparesis | 10 mg PO/IV qid × ≤12 weeks (boxed-warning duration cap) | — |
Pharmacokinetics
Onset 1–3 min IV, 30–60 min PO. Half-life 5–6 h; longer in renal failure. 30% renal excretion unchanged.
Hemodynamic effects
Mild hypotension on rapid IV push.
Respiratory effects
None directly.
Side effects
- !Acute dystonic reactions — neck spasm, oculogyric crisis, opisthotonos (especially young women, dose-dependent; treat with 50 mg diphenhydramine IV)
- !Akathisia (restlessness)
- !Tardive dyskinesia — boxed warning; risk rises with cumulative dose >12 weeks
- !Neuroleptic malignant syndrome (rare)
- !Sedation
- !QT prolongation (mild)
Contraindications
- ×Mechanical GI obstruction or perforation
- ×Pheochromocytoma (catecholamine release)
- ×Seizure disorder (lowers threshold)
- ×Parkinson's disease (worsens motor symptoms)
- ×Concurrent dopamine antagonists (additive EPS risk)
Clinical pearls
- ★DYSTONIA RISK: highest in young women, with rapid IV push, and at high doses. Pretreat with diphenhydramine 25–50 mg in higher-risk patients.
- ★PROKINETIC ACTION REQUIRES INTACT VAGUS: doesn't work in patients post-vagotomy or with severe gastroparesis from non-vagal causes.
- ★OB ASPIRATION PROPHYLAXIS: 10 mg IV with famotidine ≥30 min preop empties the stomach and raises pH — standard for non-elective C-section.
- ★TARDIVE DYSKINESIA BOXED WARNING (FDA 2009): limit chronic use to ≤12 weeks in any indication.
Other drugs in Antiemetics & Related
- Ondansetron
Blocks serotonin receptors at vagal afferents and chemoreceptor trigger zone.
- 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.
- Promethazine
H1 antihistamine with anticholinergic + antidopaminergic activity → antiemetic + sedation + antihistamine effects.
- Haloperidol
Dopamine D2 antagonist (CTZ) → antiemetic at low doses; antipsychotic/sedating at higher doses.
Suggested reading
- •Stoelting & Hines, Pharmacology & Physiology in Anesthetic Practice, 6e
- •Miller's Anesthesia, 9e
- •FDA package insert
