Oral Penicillin and Your Dog: Doses, Treatment, Risks, and More

Written by Shaunice Lewis
Published: September 18, 2022
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Penicillin is a type of antibiotic that is often prescribed to animals to help heal infections. If your veterinarian has prescribed your dog penicillin there are a few important things you should know. Read on to learn more about penicillin, its uses, and its risks.

What Is Penicillin?

As stated, penicillin is a type of antibiotic that is commonly prescribed to animals and humans to treat infections. It is a naturally occurring penicillin and was the first ever antibiotic to be discovered. There are many different types of penicillin available now, but the original form of penicillin is still used today.

Bacterial infections are the reason why penicillin is generally prescribed. However, some bacteria have become resistant to penicillin. Because of this, many veterinarians will only prescribe penicillin when they are certain that the type of bacterial infection that your dog is dealing with will be able to be treated effectively with it.

Penicillin is administered via injection. It can either be injected into a vein or even into a muscle or beneath the skin. There is also the oral form of penicillin, which works the same, but is prescribed less often and is administered orally. This type of penicillin is best taken on an empty stomach, so before you feed your dog. If, however, you find that your dog develops an upset stomach after giving it the oral medication, you may want to give it with food the next time.


Penicillin is administered via injection. It can either be injected into a vein or even into a muscle or beneath the skin.

©Walter Cicchetti/Shutterstock.com

What Is Penicillin Used for in Dogs?

Penicillin can be prescribed to dogs for treating infections that are caused by certain types of bad bacteria. It is most commonly used to treat skin infections, respiratory infections, and urinary tract infections.

Doses for Dogs

You’ll want to follow any specific dosage instructions that were given to you by your veterinarian. They will provide you with this information at the vet when you pick up your dog or the medicine. Adhere to the dosage instructions as closely as possible so that your dog can recover from its infection properly.

What Do I Do if I Miss a Dosage?

If you miss one of the dosages for your dog, you should try to give it its missed dosage as soon as possible. If the missed dosage is close to the time that you are supposed to give your dog its next dosage, you should skip the dose that you missed and just continue on with its next dose on its regular schedule. Be sure that you do not give your dog two doses at a time. This can be very dangerous. If you have any other questions or concerns about your dog’s dosage, you should get in contact with your veterinarian for further information.

What Are the Risks?

There are a few risks associated with penicillin that you should be aware of before administering penicillin to your dog. Let’s go over a few of them below.

In most cases, penicillin is considered to be a safe treatment for infections. However, there are some side effects to be aware of if you will be giving the medicine to your dog. One of the most serious side effects that are associated with penicillin is an allergic reaction called anaphylaxis. Your dog may also experience gastrointestinal distress. Here are a few things to be on the lookout for to know if your dog is having a negative reaction to the medicine:

  • Facial swelling
  • Itchiness
  • Hives
  • Rashes on the skin
  • Difficulty breathing
  • Loss of appetite
  • Vomiting
  • Diarrhea

If you notice any of the above side effects in your dog you should stop giving the penicillin doses and get in contact with your veterinarian right away. They will be able to let you know whether you should continue with the treatment or not and may present other treatment alternatives for your dog.

To help reduce the instances of upset stomach in your dog, you may want to give your dog its medicine along with food. This can reduce the chances of your dog developing an upset stomach or experiencing vomiting or diarrhea. If you’ve tried giving your dog the medicine with food and it still has these symptoms, you should contact your veterinarian for further instructions.

The more serious side effects of penicillin are rare but they are possible. Your dog could experience irregular breathing patterns, fever, rash, or swelling around its face. If you notice any of these symptoms please reach out to your veterinarian right away so that your dog can be treated.

dog with a rash

If your dog breaks out in a rash, he may be having a reaction to penicillin.


How Should Penicillin Be Stored?

When you receive penicillin for your dog, it’s important that you store it properly to keep the medicine from going bad and to keep it safely out of reach of children.

Liquid, oral penicillin should be stored in the refrigerator since it must be kept cool. However, you do not want the medicine to freeze so do not store it in the freezer. Any medication that is not used within 14 days of receiving it should be discarded.

Also, be sure to keep the medicine away from heat and moisture. If exposed to either of these, the medicine may break down and become less effective. The best place to store oral penicillin is in the refrigerator where it will stay liquified at a cool temperature and away from heat and moisture.

Possible Drug Interactions

If you are already giving your dog other medications, it’s important that you discuss this with your vet if they don’t already know as some medications can interact with oral penicillin.

In some cases, a veterinarian may even prescribe two different medications for your dog to take, and may even anticipate that an interaction may occur. Under the care of the veterinarian, they will monitor your dog closely to make sure that the medications are working as intended together and will adjust your dog’s dosages if necessary.

Here is a list of drugs that could potentially have interactions with penicillin:

  • Cephalosporins
  • Aminoglycosides
  • Rifampin
  • Bacteriostatic antibiotics
  • Oral anticoagulants
  • Probenecid
  • Antacids
  • Neomycin
  • Aspirin
  • Heparin
  • Phenylbutazone
  • Indomethacin

If your dog is currently taking any of the above medications you should let your veterinarian know before they begin your dog on its prescription oral penicillin. Your vet will monitor your dog for any possible interactions and adjust the dosage or stop the regimen accordingly.

Can I Stop Giving My Dog Oral Penicillin if It Seems Better?

If you notice that your dog seems to be feeling a lot better, you may wonder if it’s necessary to finish giving your dog all of its doses. It is advised that you continue giving your dog its doses, even if it appears that your dog is feeling better. Dogs will need to finish their full course of antibiotics for very important reasons.

The first reason why dogs will need to complete their full course of antibiotics is that different illnesses or health issues will require different lengths of antibiotics to kill off the bacteria. For example, if your dog has a simple wound infection, it may only take about a week of oral medication to clear up the infection.

However, if your dog has a more complicated or serious infection, it could take months of dedicated treatment in order to clear it up. Your pet may look like it’s doing better on the outside (which is a great thing) but you will not know if the bacterial infection has been completely resolved.

If you stop the rounds of medicine too soon, the infection may persist since the bacteria weren’t completely eliminated, which could result in the return or prolonging of whatever illness or infection your dog was dealing with.

Another reason why you don’t want to end your dog’s treatment early is because of the Acceleration of Antimicrobial Resistance (AMR). This is when there is a change in microbes like viruses, bacteria, or fungi, in which they become more resistant to drugs that were previously used to treat them.

What this means is that if you stop your dog’s treatment too early, the bacteria that weren’t killed off have the chance to become more resistant to the medication in the future, making it harder to treat your dog for the illness—especially if the infection persists.

Making sure that you give your dog its full dosage of the medicine will not only help your dog heal faster, but it can also help it remain healthier for longer and reduce the chances of leftover bacteria becoming resistant to treatment in the future. This is why it is always important to follow the instructions given to you by the veterinarian that go along with the medication as closely as you can.

If you have any further questions or concerns about your dog’s oral penicillin, be sure to reach out to your veterinarian and they will be able to help you get your dog the proper treatment they need to be on track to fully heal from their infection.

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The photo featured at the top of this post is © megaflopp/Shutterstock.com

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Freelance writer specializing in natural health and wellness.

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  1. Ped MD, Available here: https://www.petmd.com/pet-medication/penicillin
  2. VCA Animal Hospitals, Available here: https://vcahospitals.com/know-your-pet/penicillins---general
  3. Vet Voice, Available here: https://www.vetvoice.com.au/ec/pet-ownership/does-my-pet-have-to-finish-their-antibiotics/