They commonly get nailbed/toenail type infections that can cause swelling and be painful. The infection can be mixed between bacterial and fungal...and much like us, nonresponsive to topicals and require oral medications. And as always, I feel a vet visit will yield the most affective medications.
IF you are reluctant to go to a vet. For now you can start with diluted betadine soaks (drug store) it is brown and will stain the foot...you can ask for a chlorohexiderm solution that doesn't stain. Regardless of bacteria or fungal the solutions do help. You would soak the foot twice a day for about 5-7 minutes. Dry well and you can purchase a topical antifungal spray or drops or cream. Apply this for 2-3 days. If you don't see improvement you need to go to a vet.
Dr.V
Dr. D.A. Vamvakias
Veterinarian