Feline Antiemetics: Maropitant, Ondansetron & Metoclopramide

Vomiting and nausea are among the most common — and most dangerous — problems in caring for a sick cat, because not eating can quickly spiral into an emergency like hepatic lipidosis. Antiemetics break that cycle and restore "a body that can eat." This article compares the three main antiemetics and their practical cautions.

1. The three main antiemetics at a glance

For severe cases, maropitant + ondansetron are combined (different pathways = synergy). Metoclopramide is used more as a "prokinetic to push the gut" than as a pure antiemetic.

2. Maropitant (Cerenia)

• Who it is for: acute vomiting, motion sickness, cats refusing food from nausea, peri-operative vomiting prevention, pre-emptive management in chronic disease.
• Action: blocks the receptor (NK-1) for substance P, a vomiting-signal molecule. Works at both the brain vomiting center and the GI tract for broad suppression.
• Dosing: injectable + oral tablets. With a long half-life of ~13-17 hours, once daily is enough.
• Dose: typically ~1 mg per kg body weight (oral). Follow your vet for exact dose and duration.
• Cautions: stinging pain on injection (eased by refrigerating and injecting slowly); some cats may actually lose appetite (see case below); rare allergy.

3. Ondansetron (Zofran)

• Who it is for: severe nausea — uremic nausea from kidney disease, chemo-induced vomiting, strong queasiness.
• Action: blocks the 5-HT3 (serotonin) receptor. A different pathway from maropitant, so they complement each other.
• Dosing: short half-life, usually 2-3 times daily. Oral and injectable.
• Cautions: generally safe but can cause constipation — watch cats already prone to it.

4. Metoclopramide

• Who it is for: when the problem is delayed gastric emptying / low gut motility rather than vomiting itself (food sitting in the stomach too long).
• Action: dopamine block + prokinetic (promotes gut motility). Cats have few brain dopamine receptors, so its central antiemetic effect is weaker than in dogs — it is used more for motility than vomiting.
• Dosing: before meals or as a constant-rate infusion (CRI).
• Cautions: at high doses or long-term, rare neurologic signs (tremor, restlessness — extrapyramidal signs).

5. Mirtazapine — not an antiemetic, but relevant

Mirtazapine is strictly an appetite stimulant, but it also has anti-nausea (5-HT3) effects, so it is often mentioned alongside antiemetics. A transdermal form (applied to the inner ear) makes dosing easy.

6. Real case: Ari, a cat with chronic IBD

Ari (2.8 kg), living with chronic IBD, was given 4 mg of maropitant every day for pre-emptive vomiting control. But at some point the response to mirtazapine (appetite stimulant) dropped sharply.

Reviewing the care-log data, the decline lined up exactly with "when daily maropitant began." Maropitant has a long half-life (13-17h), so daily dosing can accumulate in the body, and in some cats that itself appears as an appetite-suppressing side effect.

So the dose was changed to every-other-day — and mirtazapine's appetite effect returned, with overall appetite recovering.

References

• Quimby JM, Lunn KF. Mirtazapine as an appetite stimulant and anti-emetic in cats with chronic kidney disease. Vet J. 2013.
• Plumb DC. Plumb's Veterinary Drug Handbook (Maropitant, Ondansetron, Metoclopramide).