Quick answer: There is only one iron rule in pet medication: every dosage and medication decision is made by the veterinarian. Common human drugs such as acetaminophen (paracetamol) and ibuprofen are clearly toxic to cats and dogs—never give them on your own. If a pet swallows something by mistake, immediately note the drug name, quantity and time, bring the packaging and contact your veterinarian, and do not induce vomiting yourself.
Information checked to 2026-10-12Sources: publicly available database of the ASPCA Animal Poison Control Center, publicly available information from the American College of Veterinary Internal Medicine (ACVIM), and general Hong Kong veterinary clinical practice
Pet medication is one of the easiest areas for things to go wrong in Hong Kong pet-owning households. The same drug name that is fine for a human can poison a cat or dog; the same dose can carry more than ten times the risk for a 5 kg cat compared with a 30 kg dog. These differences cannot be fixed by 'being a bit more careful'—they require a veterinarian's professional judgment.
This article is the overview of the PetChill Blog pet medication safety series. It explains the safety principles from three angles: first, who is responsible for dosage and medication decisions (entirely the veterinarian); second, the toxicity of human drugs to cats and dogs and what to do if they are swallowed; third, the discipline of prescription courses (antibiotics, dewormers) and how to handle side effects. Everything here covers general principles only—it will not teach you to self-medicate, nor can it provide any specific dosage advice.
1. The first iron rule: every dosage and medication question must be decided by a veterinarian
Many 'pet medication dosage charts' online look convenient, but they make a fatal mistake: they treat a drug as a number that can be plugged into a formula. In reality, when a veterinarian prescribes, they must consider all of the following, and none of these factors can be assessed by an owner at home:
- Actual body weight and body condition score: not 'about 5 kg', but including dehydration, muscle wasting and fat proportion.
- Drug type and concentration: two things both called 'antibiotics' can have completely different ingredients, formulations and absorption rates.
- Liver and kidney function: metabolism and excretion of drugs rely mainly on the liver and kidneys; if function is poor, adjustments are needed.
- Other medications being taken at the same time: drugs can amplify each other's toxicity or reduce effectiveness.
- Age and physiological state: medication considerations for kittens and puppies, pregnancy, lactation and senior pets are completely different.
- Illness and complications: fever, dehydration and vomiting all change drug absorption.
Therefore every dosage and medication question must be decided by a veterinarian. The owner's job is not to do calculations but to report accurately: the pet's weight, what was eaten, when, how much, what symptoms, whether there are other chronic illnesses and what medications are being taken. The clearer this information, the more accurate the veterinarian's judgment.
Another often-overlooked principle: complete the full course. Antibiotics must not be stopped 'because the pet seems better', because disappearance of symptoms only means the number of bacteria has decreased, not that they are fully cleared; stopping early easily leads to relapse and promotes resistance. Likewise, do not 'double the dose to get better faster' on your own—drug toxicity is often dose-related.
2. Why can't cats and dogs share the same drug?
Although cats and dogs are both pets, they metabolise drugs very differently. The classic example: a cat's liver has relatively limited ability to handle certain drugs, so some drugs that are safe for dogs can be fatal to cats. This is not because 'cats are weaker' but because of physiological differences between species.
| Comparison | Cats | Dogs | Meaning for medication |
|---|---|---|---|
| Liver metabolism speed for some drugs | Slower (low activity of specific metabolic pathways) | Relatively faster | For the same ingredient, cats may need a lower dose or it may be completely contraindicated |
| Examples of high-risk ingredients | Acetaminophen, pyrethroids, some human anti-inflammatory painkillers | Ibuprofen, some human anti-inflammatory painkillers | Dog spot-on products or drugs must not be used on cats |
| Typical weight range | Generally 3 to 5 kg | From 2 kg to over 40 kg | Dosage must be calculated by actual body weight, never 'approximately' |
| Risk when dehydrated | Drug concentration rises faster | Also at risk | Use medication more cautiously with vomiting, diarrhoea or kidney disease |
| Grooming habits | Grooms frequently, easily licks topical medication | Relatively less | Topical spot-on products must be applied where the pet cannot lick |
The most practical conclusions are three sentences: dog products must not be used on cats; cat products must not be casually increased for dogs; any cross-species or cross-brand substitution must be checked with a veterinarian first. In particular, dog flea products containing pyrethroids can cause tremors, seizures and other neurological signs in cats after contact—this is an emergency.
3. How toxic are human drugs? Acetaminophen and ibuprofen must be completely avoided
The most common scenario in Hong Kong households is 'whatever medicine we have, just give the pet a bit'. The following categories are common human drugs long listed as toxic to pets in the ASPCA Animal Poison Control Center database and must be completely avoided.
| Human drug/ingredient | Human use | Risk to cats | Risk to dogs | Common poisoning signs |
|---|---|---|---|---|
| Acetaminophen (paracetamol) | Fever and pain relief | Extremely high; even small amounts can cause serious harm | High (dose-related) | Rapid breathing, blue-purple gums or tongue, facial swelling, depression, jaundice |
| Ibuprofen | Anti-inflammatory pain relief | High | High | Vomiting, black stool, abdominal pain, kidney damage |
| Aspirin | Pain relief, blood thinning | High (slow metabolism, easily accumulates) | Moderate to high | Gastrointestinal bleeding, anaemia |
| Cold and cough medicines containing pseudoephedrine or dextromethorphan | Cold and cough treatment | High | High | Fast heart rate, restlessness, tremors, drowsiness |
| Human oral steroids | Anti-inflammatory, immune suppression | Must be prescribed by a veterinarian | Must be prescribed by a veterinarian | Increased thirst and urination, stomach upset; long-term use has other metabolic effects |
| Human topical ointments (containing steroids or antifungals) | Skin problems | Risk if licked | Risk if licked | Stomach upset; systemic effects possible after absorption |
Remember three key points:
- 'A small human dose' is not the same as 'a safe dose for a pet'. Acetaminophen has a very narrow safety margin in cats; there is no such thing as 'try a little and see'.
- Combination products are the most dangerous. One cold capsule may contain a fever reducer, an antihistamine, pseudoephedrine and other ingredients, any one of which can cause harm.
- Topical medications can also poison. A pet licking ointment applied to itself or to the owner's skin can be enough to cause a systemic reaction.
If you have these medications at home, it is best to store them in a sealed medicine box that pets cannot reach, not on the coffee table, bedside table or in a handbag. For more information on household toxins, see our cat forbidden food list and cat toxic plant guide.
4. What to do if your pet swallows something: the first 30 minutes decide the outcome
Swallowing something by mistake is a race against time. The flow chart below covers general principles, but please note: all management decisions must still be made by a veterinarian; the owner's role is to 'report accurately, contact quickly, and avoid doing the wrong thing'.
| Timeframe | What to do | What not to do |
|---|---|---|
| Immediately (0–5 minutes) | Remove the medication and packaging, and settle the pet in a safe, quiet space | Do not shout or startle the pet, to avoid it searching again |
| 5–15 minutes | Note the drug name, ingredients, dose per tablet, how many were eaten, the time, the pet's weight and symptoms | Do not induce vomiting yourself, do not feed milk, salt water, oil or any 'antidote' home remedy |
| Within 15 minutes | Call your veterinarian or emergency centre and explain the above information item by item | Do not wait for symptoms to appear before calling—many poisonings are delayed |
| Before going to the clinic | Bring the drug packaging or a clear photo; if there is vomit, bag it and bring it | Do not feed any food or medication on your own |
| After arrival | Provide a full medication history, chronic illnesses, and current medications and supplements | Do not conceal information or add medication yourself |
Several common misconceptions need correcting:
- 'Inducing vomiting is basic first aid'—wrong. Unless your veterinarian explicitly instructs you on the phone, inducing vomiting yourself can cause corrosive substances or sharp objects to injure the oesophagus again, and can cause aspiration into the airway.
- 'A little bit should be fine'—not necessarily. Toxicity from acetaminophen, flea product ingredients and others does not change linearly with 'how much'; a small amount can already cause harm.
- 'Wait and see if there are symptoms'—the most dangerous. Obvious symptoms of many poisonings are delayed by hours to a day or two; delaying veterinary care means missing the golden window.
If your pet has persistent vomiting, see the cat vomiting guide to distinguish warning signs; for emergencies such as seizures, difficulty breathing or inability to stand, go straight to the pet emergency first aid guide and take your pet to the clinic immediately.
5. Antibiotic courses: finish them, note side effects, do not stop on your own
Antibiotics are among the most commonly prescribed drugs by veterinarians and also the class with the most side-effect complaints. Many owners stop the medication themselves when the pet seems better or when the pet has stomach upset after taking it—this is the most common and most regrettable mistake: an incomplete course leaves bacteria not fully cleared, easily causing relapse, and the next time a stronger drug is needed.
The following table covers how to respond to common antibiotic side effects. Please note: this only helps you judge 'when to contact the veterinarian immediately' and is not a substitute for veterinary instructions.
| Side effect | Common cause | What you can do at home first | When to contact the veterinarian immediately |
|---|---|---|---|
| Loss of appetite | Bitter taste, stomach upset, mild nausea | Confirm each dose is finished; check with the veterinarian whether it can be given with food; maintain water intake | Complete refusal to eat for more than 24 hours, or obvious deterioration in alertness |
| Diarrhoea or soft stool | Gut flora disrupted | Ensure adequate water; do not suddenly change food at the same time | Blood in stool, black stool, multiple episodes of diarrhoea in a day, vomiting at the same time |
| Constipation | Insufficient water, changed gut motility | Increase wet food proportion and water intake | No bowel movement for more than 48 hours, abdominal bloating or pain, straining without passing stool |
| Vomiting | Taking medication on an empty stomach, stomach irritation | Check with the veterinarian whether it can be given with food and try again | Continuous vomiting, vomiting blood, unable to keep any medication down |
| Skin rash, facial swelling | Drug allergic reaction | These situations should not be managed at home | Immediately—this is an emergency |
| Lethargy, tremors, seizures | Severe adverse reaction | These situations should not be managed at home | Immediately—this is an emergency |
When antibiotics cause diarrhoea, many veterinarians recommend supplementing with probiotics, but probiotics and antibiotics should be given about two hours apart, otherwise the antibiotic will kill the probiotics too, wasting them. If your veterinarian agrees to probiotic supplementation, consider VetriScience Cat Probiotic Chews 60 pieces (duck flavour), HK$195 (price subject to the current price shown on the online store). It must be emphasised: supplements are supportive only, cannot replace veterinarian-prescribed antibiotics, and must not be used on your own to 'treat' diarrhoea.
As for giving the medication itself, if every dose turns into a battle with your cat, see our cat medication guide, which covers the details of three main methods: by hand, hiding in treats, and using a pill popper.
6. Deworming safety: calculate by weight, never swap species, frequency decided by the veterinarian
Dewormers are another class of medication often 'handled on one's own'. Many owners think dewormers are health supplements, but they are drugs, and misuse can cause neurotoxicity, especially in cats. There are three safety principles:
- Must be calculated by actual body weight. Dewormers are not like vitamins; you cannot 'give approximately'. Estimating weight wrongly can easily lead to overdose or underdose.
- Cat and dog products must not be swapped. Some dog flea and tick ingredients are clearly toxic to cats and must never be applied to cats 'in a smaller amount'.
- Kittens, pregnant and ill pets need extra caution. These situations must be assessed by a veterinarian before medication is used.
| Deworming item | General recommended frequency (subject to veterinary instructions) | Notes |
|---|---|---|
| Internal parasites (roundworm, hookworm, tapeworm) | More frequent for kittens and puppies; adult pets generally every one to three months | Calculated by weight; do not split doses on your own |
| External parasites (fleas, ticks) | Monthly, or according to product label | Cat and dog products must not be swapped |
| Heartworm prevention | Mosquitoes are present year-round in Hong Kong; most are monthly or according to product instructions | In some cases a blood test is needed first; see the heartworm prevention guide |
| Ear mites, mange | Medication decided after veterinary diagnosis | Do not buy ear drops and use them indiscriminately |
Regarding dewormer safety, the right question is not 'which brand is especially safe' but 'is this drug appropriate for this pet, this weight and this health condition, according to the veterinarian's judgment'. Common dewormer brands differ in ingredients, formulation and suitable age; some target only internal worms, some also treat external parasites, and some require a blood test first. These details must be decided by a veterinarian. For more local deworming arrangements, see the cat deworming guide.
7. Dosage calculation: why you cannot copy online formulas
'How can I quickly calculate an emergency drug dose for my pet using a simple formula?' is a question many people search, but the answer is: without veterinary instructions, any self-calculated dose should not be used.
| Factors often ignored by online formulas | Real impact |
|---|---|
| Drug concentration and formulation | The same ingredient can come as 10 mg and 100 mg tablets; the wrong tablet is already a tenfold difference |
| Liver and kidney function | Pets with slower metabolism need a reduced dose or a different drug |
| Dehydration and electrolyte status | Affects drug distribution and toxicity |
| Other medications being taken | Can amplify each other's side effects |
| Pet's age | Safe ranges for the young and the elderly are very different from adults |
| Whether the product is human or veterinary | Human tablets usually cannot be accurately split in half; cutting errors can be large |
So the truly safe approach is:
- Use only veterinarian-prescribed medications and veterinarian-specified doses.
- Use the measuring tools provided by the veterinarian (syringe, medicine spoon, original dispenser), not a rough estimate with a kitchen spoon.
- Check the drug name and expiry date before each dose, to avoid mixing up old medication or family members' medication.
- Record each dose and time, and show it to the veterinarian at follow-up.
- If you miss a dose, do not give double next time; instead call the veterinarian to ask how to make it up.
8. Storage and management: three habits to reduce accidental ingestion
Many poisoning cases do not happen outdoors but on the coffee table and bedside table at home. The following three habits can greatly reduce the risk:
- Store human and pet medications separately, preferably in a lidded medicine box that pets cannot open; keep prescription medications in their original labelled packaging.
- Do not store medication in food containers, and do not mix medication into a whole bag of treats (the full dose may not be eaten).
- Dispose of expired medication properly: in Hong Kong, it is not recommended to flush medication down the toilet or throw it in the bin. You can return it to a pharmacy's medication return arrangement; there have been cases of pets being poisoned after eating old medication from the bin. If in doubt, ask your veterinarian or pharmacist.
If your pet is on long-term medication (for example, for the heart, kidneys, joints or endocrine conditions), it is advisable to keep a 'medication record book' noting the drug name, dose, start date and each blood test result, and show it directly to the veterinarian at follow-up. This allows the veterinarian to spot side effects or the need for dose adjustment more quickly.
9. When to see a veterinarian immediately: emergency warning list
If any of the following occurs, do not wait and do not observe—call a nearby veterinarian or emergency centre immediately:
| Emergency warning sign | Possible meaning |
|---|---|
| Rapid breathing, blue-purple gums or tongue | Acetaminophen poisoning, lack of oxygen |
| Seizures, tremors, sudden inability to stand | Neurotoxicity, severe allergy |
| Large-volume vomiting, vomiting blood, black stool | Gastrointestinal bleeding |
| Facial swelling, generalised hives | Acute allergic reaction |
| Difficulty urinating or no urine at all | Urinary obstruction (especially high risk in cats) |
| Extreme lethargy, cannot be roused | Systemic poisoning |
In an emergency, contact your veterinarian immediately; this article is for reference only and cannot replace veterinary diagnosis. For nighttime emergency arrangements in Hong Kong, see the pet emergency first aid guide and Hong Kong pet veterinary care information, but please note that clinic phone numbers and service hours may change from year to year—call to confirm before setting off.
Summary: there is only one road to safe medication
There are no shortcuts to pet medication safety, and no 'mum's secret recipe'. What you can do is remember three things: first, every dosage and medication question is decided entirely by the veterinarian; second, human drugs, dog drugs and old drugs must never be applied to cats or dogs on your own; third, complete the full course, note side effects, and seek veterinary care immediately if warning signs appear. Follow these three and most avoidable medication accidents will stay further away from your pet.
This article is general health information and does not constitute diagnosis or treatment advice. Consult a registered veterinarian for any medication decision. Information checked to 2026-10-12.
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