Metoclopramide CRI

Centrally-acting dopamine (D2) antagonist with antiemetic and prokinetic effects. Blocks dopamine in the chemoreceptor trigger zone (antiemetic effect) and increases lower esophageal sphincter tone and gastric emptying via cholinergic enhancement (prokinetic effect). Crosses the blood-brain barrier; extrapyramidal signs can develop at higher doses or with prolonged use. Reduces gastric pH minimally; does not block 5-HT3 receptors at typical CRI doses.

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Clinical background

Metoclopramide is the workhorse antiemetic and gastric prokinetic in small-animal practice. It is most commonly given as a CRI in patients with ongoing nausea, vomiting, gastric stasis, or reflux esophagitis, where intermittent dosing every 6–8 hours doesn’t provide stable coverage. A separate higher-dose protocol is published for laryngeal paralysis surgery in dogs, where intraoperative metoclopramide reduces gastroesophageal reflux and the risk of aspiration after surgery.

Pharmacology

Centrally-acting dopamine (D2) antagonist with antiemetic and prokinetic effects. Two distinct mechanisms:

1. Antiemetic: blocks dopamine in the chemoreceptor trigger zone, reducing the central drive to vomit.
2. Prokinetic: increases lower esophageal sphincter tone and accelerates gastric emptying via enhanced acetylcholine release at the muscularis. The prokinetic effect is upper-GI specific — metoclopramide does not meaningfully alter colonic motility.

Metoclopramide crosses the blood-brain barrier. Extrapyramidal signs (restlessness, involuntary movements, dystonia-like posturing) can develop at higher doses or with prolonged infusions, and are more common in young puppies and geriatric dogs. The signs typically resolve within hours of stopping the infusion.

Indications

Primary use cases for the CRI form:

• Persistent nausea or vomiting refractory to intermittent dosing
• Gastric stasis, ileus, or delayed gastric emptying (post-laparotomy, pancreatitis, parvoviral enteritis)
• Reflux esophagitis prevention or treatment, especially perioperative
• Brachycephalic and laryngeal-paralysis patients to reduce regurgitation and aspiration risk

Other antiemetics (ondansetron, maropitant) are preferred in cats per Plumb’s — metoclopramide’s antidopaminergic mechanism is less effective in feline emesis, which has stronger 5-HT3 and NK1 components. Other prokinetic agents (cisapride) are similarly preferred for prokinetic indication in cats. Use metoclopramide in cats when the preferred alternatives aren’t available.

Dosing

• Dogs and cats, standard antiemetic / prokinetic CRI: 0.04–0.09 mg/kg/hr (1–2 mg/kg/day) IV
• Dogs, laryngeal paralysis surgery (intraoperative): 1 mg/kg IV loading dose followed by 1 mg/kg/hr IV CRI intraoperatively, dropping to 0.083 mg/kg/hr IV CRI postoperatively for a total treatment duration of 24 hours

The default in this calculator is 0.04 mg/kg/hr, the low end of the standard antiemetic range — a conservative starting dose. Titrate up to 0.09 mg/kg/hr if clinical signs persist.

For intermittent (non-CRI) administration, the dose is 0.2–0.5 mg/kg every 6–8 hours PO, SC, IM, or IV. A higher dose (1 mg/kg IM/SC) may be needed for chemotherapy-induced emesis.

Administration

Stock concentration is 5 mg/mL in 10 mL vials (50 mg per vial). Compatible diluents per Plumb’s:

• 0.9% sodium chloride
• 5% dextrose
• Lactated Ringer’s
• Ringer’s

Once added to a fluid bag, solutions are stable at room temperature for 24 hours. Discard if discoloration occurs.

The calculator’s default 40 µg/mL preparation (10 mg in 250 mL, or 20 mg in 500 mL) covers the standard antiemetic CRI dose range across most patient sizes. A 20 µg/mL preparation (5 mg in 250 mL) is provided for small patients where the more concentrated prep would run below volumetric-pump precision. The 1000 µg/mL syringe preparation (50 mg in 50 mL of 0.9% NaCl) is provided for the laryngeal-paralysis intraoperative protocol, where the 1 mg/kg/hr rate would otherwise demand impractically high carrier-fluid volumes on the more dilute preps.

Drug interactions

• Anticholinergics (atropine, glycopyrrolate) antagonize the prokinetic effect — give the prokinetic indication a different drug if anticholinergics are required.
• Phenothiazines and butyrophenones (acepromazine, droperidol) potentiate extrapyramidal effects — avoid concurrent use or watch carefully for restlessness and involuntary movements.
• CNS depressants (opioids, sedatives, anesthetics) — additive sedation.
• Chloramphenicol, calcium gluconate, and other incompatible drugs — do not co-administer in the same line; consult Plumb’s compatibility tables for specifics.

Adverse effects

The two effects to watch most closely:

1. Extrapyramidal signs — restlessness, involuntary movements, dystonia-like posturing, head bobbing. More common in puppies and geriatric dogs, with prolonged infusions, or at doses above the standard antiemetic range. Stop the infusion if signs develop; resolution within hours is typical. Diphenhydramine has been used as a rescue agent.
2. GI obstruction risk — metoclopramide is contraindicated in patients with mechanical GI obstruction or perforation. The prokinetic effect against an obstruction can cause perforation or worsen tissue damage. Confirm patency before starting a prokinetic CRI in patients with a history suggestive of obstruction.

Less common: sedation, diarrhea, hypotension on rapid IV injection.