Pet Factsheets

Antibiotic treatment

Since the discovery of penicillin by Alexander Flemming in 1928, antibiotics have saved millions of lives, in both human and veterinary medicine. They are an invaluable tool used against many diseases and are incredibly useful in veterinary as well as human medicine.

What are antibiotics?

Antibiotics are important medicines used to treat bacterial infections; they work by killing or slowing the growth of harmful bacteria. There are many types of antibiotics. It is important to remember that antibiotics are only effective against bacteria and there are many other ailments such as viruses and fungal infections that cannot be treated with antibiotics. Some of the more common antibiotics include: 

  • Penicillins, eg penicillin G and amoxicillin. 
  • Cephalosporins, eg cefaclor, cefadroxil, cefalexin, cefovecin, and ceftiofur. 
  • Tetracyclines, eg tetracycline, minocycline, and doxycycline. 
  • Aminoglycosides, eg gentamicin and amikacin. 
  • Lincosamides, eg clindamycin, lincomycin, and pirlimycin. 
  • Suphonamides and trimethoprim, eg co-trimoxazole. 
  • Nitroimidazoles, eg metronidazole, ronidazole, and tinidazole. 
  • Quinolones, eg ciprofloxacin, enrofloxacin, levofloxacin and norfloxacin. 
  • Macrolides, eg erythromycin, azithromycin, clarithromycin, and tylosin. 

What are the potential dangers of using antibiotics?

Antibiotics are designed to 'kill' bacteria either directly or by stopping their growth to the point where they die off, and some types of antibiotics are not selective about what bacteria they kill. This means that some antibiotics may kill off the 'friendly' bacteria within the digestive system as well as the harmful ones, which can cause significant side effects. Gastrointestinal signs including nausea, vomiting and diarrhoea are relatively common and this may be due to damage to the biome in the gut when friendly bacteria are killed as well as the harmful ones.  

When antibiotics are used inconsistently or at doses that are too low to be effective, bacteria can form resistance to these antibiotics rendering them useless for treatment of the targeted infection. For this reason, antibiotics must be given exactly as directed by the vet for the specified number of times daily and for the specified duration of therapy.  

Adverse reactions can occur to any medication and in any animal. There are always risks involved with any drug, and no one drug can ever be 100% safe in all situations. Adverse reactions can occur, but by selecting appropriate antibiotics and by giving the correct dose for the correct amount of time we can minimise the risks.  

Side effects of antibiotics can take many forms, but severe reactions are rare and the risks of not treating an infection outweigh any potential risk of antibiotic treatment if drugs are used exactly as prescribed by the vet. Your cat may develop an allergic reaction to antibiotics which usually appears as itchy skin, hives, rashes, and sometimes a swollen mouth or face. Rarely some antibiotics trigger an auto immune response which can lead to joint pain, swelling and lameness.  

Some antibiotics can have effects on blood cell production, and signs of problems might include loss of appetite, depression and unwillingness to exercise or jump. Neurological signs such as seizures, staggering and head tilt are seen in rare cases with some types of antibiotic. Some drugs can’t be used in young animals or pregnant queens due to risks to the developing kittens such as damage to bone growth. Some fluoroquinolone antibiotics (ie enrofloxacin) have been associated with blindness in cats. Other antibiotics may cause liver or kidney problems so care is needed in any animals with known problems in these organs.   

If your pet is prescribed medication make sure you read the information sheet that comes with the drug and ask your vet if there are any particular signs you should be watching out for. Always monitor your pet closely for side effects whenever they are on medication, and if you are concerned then you should speak to your vet immediately. And, remember the importance of giving the antibiotics exactly as the vet has prescribed.  

When are antibiotics useful?

Antibiotics have a very important role in veterinary treatment, and without antibiotics, we would be able to treat many conditions far less successfully. 

Antibiotics do not work against viral or fungal infections. However, cats may develop a secondary bacterial infection as a consequence of damage caused by viral and fungal infections, and in this circumstance your vet may prescribe antibiotics. 

Antibiotics are useful in cases of bacterial infection (eg abscesses, respiratory infection, urinary infections, skin infections, eye infections), and to prevent infection in wounds (eg trauma or after surgery). In some circumstances your vet will administer antibiotics to your pet around the time of an operation to prevent bacterial infections in the wound. 

How does my vet know which antibiotic to use?

Different antibiotics are effective against different types of bacteria; some will be effective against many types of bacteria (broad spectrum antibiotics) and others may only work against one or two types of bacteria (narrow spectrum antibiotics). 

Ideally, a culture and sensitivity test should be carried out before starting any antibiotic treatment. This involves taking a sample of any discharge from the affected area, (eg a wound, bodily fluid or from an orifice). The sample is then sent away to a laboratory where the bacteria are grown and then tested against a variety of antibiotics to see which is most effective at killing the bacteria.  

Because it may take a few days to determine which bacteria are causing the problem, your vet may start treatment with a broad spectrum antibiotic while waiting for the results of the culture and sensitivity tests. Some vets may do an in-office procedure called a gram stain, or they may use professional experience in treating infections to determine which broad spectrum antibiotic to start with. Culture and sensitivity testing is increasingly important because of the treatment challenges veterinarians face due to antibiotic resistance. It is important to make sure that the antibiotic used will be effective, because the sooner the infection can be treated the best chance your cat has of recovering.  

How are antibiotics administered?

Antibiotics can be given as tablets, capsules or liquid by mouth, or your vet may give an injection under the skin, into the muscle or intravenously. In rare cases your vet may show you how to give injections to your pet at home. If your pet has a skin infection they may be prescribed an antibiotic cream to apply directly onto the lesion or an antibiotic shampoo to bathe the infected area. If you are responsible for giving antibiotics to your cat you must make sure that you give the treatment as prescribed, which means giving the right dose at the right time and making sure you complete the treatment course (even if your pet appears to have got better after only a few days).

If you miss a dose of antibiotic you should refer to the information sheet you were given with the medication, or if you don’t have this sheet, contact your vet for advice. It is best to not consult antibiotic drug information sheets written for humans as they typically do not mention any of the important considerations for use of the antibiotic in animals. Most antibiotics have a wide safely margin and often it will be simply a case of giving the dose as soon as you remember, and the next dose at its usual time. However, do not double up doses unless specifically instructed to do so by your vet as this can lead to more side effects.

What about antibiotic resistance?

Antibiotic resistance is fast becoming a serious problem in human medicine, and in some cases is following the same path in veterinary medicine. Many of the same antibiotics that are used in human medicine are used in animals. 

Bacteria are living organisms and can adapt and find ways to survive the effects of an antibiotic, especially if the antibiotics are given intermittently or at doses lower than those required to be effective. Over time these bacteria may become 'antibiotic resistant', meaning that the antibiotic no longer works against that strain of bacteria. Each time we use an antibiotic we run the risk of creating a resistant bacteria which is why it is so important to only use antibiotics when they are absolutely necessary.  

The main cause of antibiotic resistance is failure to complete a full course of treatment or missing too many doses during the prescribed course of treatment. Bacteria have varying degrees of sensitivity to an antibiotic. Usually the most sensitive bacteria in an infected tissue are killed first with the more resilient bacteria requiring subsequent doses of antibiotic to achieve a kill. If antibiotics are stopped too soon then the more resilient bacteria remain alive; they “remember” the exposure to the antibiotic that did not kill them, adjust their bodily defences, and reproduce creating a new colony that is less likely to be killed by that antibiotic. These bacteria can then share that information with other bacteria and resistance starts to spread through the whole population. Potentially a situation can arise whereby a bacterium becomes resistant to all known antibiotics. 

By using antibiotics less often, we can slow down the development of resistance, and antibiotics should never be used unnecessarily. Always use the correctly prescribed antibiotic, at the correct dosage and for the correct length of time. 

Antibiotics are an invaluable tool in the fight against disease in cats. However, it is essential they are treated with respect to protect the benefits they give to both veterinary and human medicine. If your pet is prescribed antibiotics remember to always follow the instructions given to you by your vet.