Antiemetic

An antiemetic is a medication against nausea and vomiting – it prevents these complaints or at least reduces them. The point of attack is directly in the vomiting centre in the brain: The substances cut off the signals there before vomiting occurs. In veterinary medicine, vets use antiemetics for dogs whenever vomiting is triggered by very different causes – whether gastrointestinal diseases, motion sickness, post-operative nausea or chemotherapy side effects.

When is an antiemetic used in dogs?

The situations in which a dog needs an antiemetic are more varied than one might initially think:

• Gastrointestinal problems: Dogs with gastroenteritis, gastric mucosal inflammation, gastric hyperacidity or general digestive disorders vomit frequently. Antiemetics relieve these symptoms until the actual cause is treated.
• Motion sickness (kinetosis): Some dogs become nauseous even on short car journeys – a real problem for pet owners travelling with their animal. Antiemetics can be given before the journey to prevent nausea and vomiting from occurring in the first place.
• Post-operative nausea: After surgery, many dogs react sensitively to the administered anaesthetic agents. An antiemetic then helps to stabilise the dog and allow recovery to proceed more calmly.
• Chemotherapy: Dogs undergoing chemotherapy often struggle with nausea and vomiting as accompanying symptoms. Antiemetics keep these side effects under control.
• Kidney diseases: In chronic kidney disease or acute kidney failure, nausea is part of the common symptom picture. Antiemetics can help the dog eat better again and retain fluid.
• Toxin ingestion or poisoning: If a dog has ingested toxins, severe vomiting often occurs. Once the poison has been removed from the body, an antiemetic can stop the persistent vomiting.

Common antiemetics in dogs

Not every antiemetic suits every situation. The choice depends on what triggered the vomiting and how the individual dog is doing at the moment.

Maropitant (Cerenia)

• Maropitant is one of the most frequently prescribed antiemetics in small animal practice. It blocks neurokinin-1 receptors in the vomiting centre, thereby interrupting the signal chain that leads to nausea and vomiting. It shows good efficacy for both acute nausea and motion sickness.
• Application: As a tablet or injection.
• Side effects: Rare; occasionally causes drowsiness or pain at the injection site.

Metoclopramide (Paspertin)

• Metoclopramide has a dual effect: it stimulates the gastrointestinal tract and simultaneously blocks dopamine receptors in the vomiting centre. This makes it particularly useful for dogs that vomit due to digestive disorders or after surgery.
• Application: As a tablet or injection.
• Side effects: At high doses, behavioural changes or nervousness may occur.

Ondansetron (Zofran)

• Ondansetron is a serotonin antagonist – originally from human medicine, now also established in veterinary medicine. It blocks serotonin receptors in the gastrointestinal tract and in the brain and is particularly used when chemotherapy, anaesthesia or severe gastrointestinal diseases are behind the nausea.
• Application: As a tablet or injection.
• Side effects: Generally well tolerated; occasionally causes constipation or drowsiness.

Dimenhydrinate (Vomex A)

• Dimenhydrinate is an antihistamine that many dog owners know primarily from their own travel medicine kit. In dogs with motion sickness, it suppresses the urge to vomit by inhibiting H1 receptors in the brain, which are responsible for motion and balance stimuli.
• Application: As a tablet or in liquid form, usually shortly before a car journey.
• Side effects: Drowsiness is the most common accompanying symptom.

Mechanism of action of antiemetics

At its core, all antiemetics aim to interrupt the signals that would activate the vomiting centre in the brain – only the exact point of attack differs depending on the active ingredient:

• Blockade of neurokinin-1 receptors (maropitant): Maropitant occupies the neurokinin-1 receptors in the brain. These receptors are centrally involved in transmitting nausea and vomiting signals – if they are blocked, the signal no longer arrives.
• Promotion of gastrointestinal motility (metoclopramide): Metoclopramide accelerates stomach and intestinal movement, so that stomach contents are transported further more quickly. Additionally, it blocks dopamine receptors in the brain, which would otherwise trigger the vomiting reflex.
• Blockade of serotonin receptors (ondansetron): Ondansetron interrupts serotonin receptors in the gastrointestinal tract and in the central nervous system. Serotonin can therefore no longer trigger a nausea stimulus.
• Inhibition of H1 receptors (dimenhydrinate): Dimenhydrinate acts on H1 receptors, which process motion and balance stimuli in the brain. If these are dampened, the urge to vomit during motion sickness is also noticeably reduced.

Side effects and risks of antiemetics

Antiemetics are effective – but no remedy is without risk. Especially with long-term use or high doses, possible side effects should be kept in mind:

• Drowsiness and sleepiness: Particularly antihistamines such as dimenhydrinate often make dogs sleepy. This is usually temporary, but anyone giving such a remedy for the first time should observe their dog closely.
• Behavioural changes: Some dogs react to metoclopramide with nervousness, restlessness or, in individual cases, even aggression. This often shows up soon after the first dose.
• Gastrointestinal problems: Occasionally – ironically – an antiemetic itself causes complaints in the gastrointestinal tract. Ondansetron, for example, can cause constipation; diarrhoea or loss of appetite also occur.
• Allergic reactions: Rare, but serious: in some cases, allergic reactions can occur – recognisable by swelling, itching or breathing difficulties. Immediate vet visit is indicated then.
• Interactions with other medications: Antiemetics can interact with other preparations the dog receives. The vet should therefore always be informed about all medications.

Precautions when using antiemetics

To ensure that antiemetics work safely and no unnecessary risks arise, a few basic points must be observed:

• Veterinary prescription: Antiemetics do not belong in the category of “just trying it out yourself”. The dose and active ingredient should always be determined by a vet – tailored to the cause of the nausea and the general condition of the animal.
• Monitoring for side effects: Observe the dog attentively during treatment. If unusual symptoms occur, one should not wait but contact the vet promptly.
• Combination with other treatments: An antiemetic combats symptoms – not the underlying disease. The actual cause must be diagnosed and specifically treated; the antiemetic accompanies this treatment but does not replace it.