It GREATLY depends on what type of Penicillin. for an 80 lb (36
kg) dog the aqueous Pen G (300,000 units/ml) dosage that I would
give is as follows: First dose = 4.5 ml INTRAMUSCULAR all
subsequent doses = 4.0 ml intramuscular every 24 hours for a total
of 5 doses Hope this helps.