Side Effect

Side effects – this is everything that a medication, a vaccination or a treatment triggers in the body without it being intended. In short: the unwanted accompanying symptoms alongside the actual healing effect.

Symptoms of a Side Effect in Dogs

After administering medication, a dog sometimes behaves differently than usual. This can be harmless – but it does not have to be. The decisive factor is what changes and how strongly.

Frequent reactions after a vaccination, 83.3 per cent of which occurred within 12 hours:

• Pain and swelling at the injection site
• Lethargy
• Loss of appetite
• Fever
• Individual episodes of vomiting

Emergency symptoms – go to the vet immediately:

• Acute swelling of lips, conjunctiva or facial skin
• Severe breathing difficulties
• Vomiting and diarrhoea shortly after administration (in dogs, gastrointestinal signs are predominant in anaphylaxis)
• Collapse or loss of consciousness (anaphylactic shock)

Medications with frequent side effects

Some medications trigger unwanted reactions in dogs more often than others. A few candidates that regularly appear in everyday life:

Painkillers (Rimadyl, Metacam): Vomiting is the most frequently observed side effect; gastrointestinal ulcers are the most common life-threatening one. Around a quarter of reported reactions affected the gastrointestinal tract. If your dog vomits, call the practice and follow their instructions regarding further administration.

Deworming treatments with avermectins: In Collie-type dogs with the P-glycoprotein gene defect, lethargy, muscle weakness, blindness, coma and fatalities were observed after high doses; a genetic test shows sensitivity in advance.

Vaccinations: Pain and swelling at the injection site, lethargy, loss of appetite, fever and isolated vomiting are common; hives and anaphylaxis are rarer. In a Japanese evaluation, 62.7 reactions occurred per 10,000 vaccinations; small dogs under 5 kilograms that received multiple vaccinations per appointment were particularly at risk.

Measures for side effects

The first reaction counts. Keep calm – and then proceed in a structured manner.

Immediate measures (from the practice): Note the time of medication administration. Take photos of skin changes while they are still visible. Do not discontinue a medication on your own authority, but call the vet practice and let them decide whether and how it should be continued.

In case of gastrointestinal problems (from the practice): Offer small portions of cooked rice with chicken. Provide plenty of water. Observe closely whether things improve or worsen.

In case of skin reactions: Do not apply your own ointments without veterinary consultation.

Many reactions depend on the dose. However, only the vet may adjust the dose.

Normal versus dangerous side effects

Knowing the difference is crucial – it determines whether you wait and see or act immediately.

Frequent and usually harmless: Pain and swelling at the injection site, lethargy, loss of appetite, fever and isolated vomiting after a vaccination.

Concerning (contact vet): Vomiting under painkillers, because gastrointestinal ulcers are the most common life-threatening side effect.

Dangerous (emergency): Breathing difficulties of any kind. Changes in consciousness. Circulatory collapse – recognisable by pale mucous membranes and a weak pulse.

How can I prevent side effects?

From the practice: Adhere to the dosage and schedule of the practice and mention all medications your dog receives at every appointment.

Are older dogs more susceptible to side effects?

Yes. For painkillers, the MSD Veterinary Manual recommends laboratory monitoring for liver damage in old animals, as they may be more susceptible to severe complications.

Can side effects also occur only after days?

Yes, that happens. Especially with prolonged administration of painkillers, the MSD Veterinary Manual therefore recommends laboratory monitoring of liver values.

What to do if the dog spits out the medication?

Do not re-administer a spat-out dose on your own authority, but ask the vet practice how to proceed.

Are there dog breeds that react particularly sensitively?

Yes. In Collie-type dogs, sensitivity to avermectins in deworming treatments is documented. For vaccinations, small dogs under five kilograms that received multiple vaccinations per appointment were particularly at risk. Always mention the breed to the vet; this belongs to the medical history.