The aim of this study is to evaluate if local treatment with penicillin of interdigital phlegmon in dairy cows is as efficient as intramuscular treatment with penicillin. Interdigital phlegmona is a common disease in dairy cows. The standard treatment is often intramuscular injection with penicillin, but local treatment with penicillin is also used in the field. The effect of the latter treatment is however not scientifically evaluated and there are no registered drugs with penicillin available for local treatment. When treating cows with intramuscular antibiotics, the entire cow is treated, leading to more antibiotics used and an increased risk of antibiotic resistance. Moreover, injections can cause pain. If local treatment with penicillin is proven to be an efficient way of treating interdigital phlegmon, it is an economic and more animal friendly alternative to intramuscular injections and also better for the environment and with less risk for antibiotic resistance.