If your vet has not suggest to you that you give your dog penicillin then DON'T! Self medicating your dog without seeing a vet is extremely dangerous. Dogs can have allergic reactions to medications like humans. See a vet!
If in fact a visit to the vet is not a viable option owed to their exorbitant fees; "self" medicating may well be preferable to taking no action and hoping that the condition self resolves. Below, find the dosage guidelines for dogs. Best wishes to Pooch for a full & speedy recovery.
dosing standards for dogs & cats
penicillin v 5.5 - 11mg per kg, every 6-8hrs
source- Veterinary Pharmacology and Therapeutics 8th ed, pg 844
source - http:/www.vetinfo.com/side-effects-penicillin.html
Side Effects of Penicillin
There are side effects that can be caused by penicillin. Side effects are rare but they can occur so it is important to be aware of them in case your dog develops symptoms.
It is possible for dogs to be allergic to penicillin. In this case, an allergic reaction can be life-threatening so it is crucial to get your dog to a vet immediately. Symptoms of an allergic reaction include problems with breathing and, in severe cases, your dog could go into shock. There is nothing you will be able to do to help your dog yourself, he will need urgent attention from a vet.
Other dogs that aren't allergic to penicillin may also develop side effects. These include:
Wind or flatulence
Digestion problems, including diarrhoea
The development of fungi
Taking the Full Prescription-
Penicillin only works properly if your dog takes the full course that was prescribed. It is common for pets to look much better a few days before the course of medication has ended. However, if you stop giving your dog the penicillin before the course is over then there is a chance the infection might return. At this point, the bacteria causing the infection might be immune to the effects of the penicillin so it will be even harder to cure your dog.
Although it can cause side effects, penicillin is an effective way of treating infections in dogs. Side effects are rare compared to the number of dogs that are prescribed penicillin but they are worth watching out for. Unless your dog has had an allergic reaction or your vet has told you to stop giving your pet the medicine, continue with the prescribed course. Soon, the infection will be gone and your dog can continue living a normal life.