This is from the animal poison control center they charge$45.00 per case charged to the owner’s phone bill. The Center will do as many follow-up calls as necessary in critical cases, and at the owner’s request will contact their veterinarian. Stated below it recommends possible antihistamines to help if it is infact the plant that in causing the problem. If it doesn't subside soon maybe anesthetizing him and possible getting a close look in there might be a good idea. Make sure its not an abcess, bad tooth or even possibly a tumor. In the mean time you can try feeding him baby food so he doesn't have to chew it. Might be easier for him to eat since his mouth is sore.
Common Name: Fiddle-Leaf Philodendron
Scientific Name: Philodendron bipennifolium
Toxic Principle: calcium oxalate crystals
Clinical signs: oral irritation, intense burning and irritation of the mouth, lips, tongue, excessive drooling, vomiting, difficulty in swallowing.
Common name(s) Cordaturn, horsehead, philodendron, red emerald, red princess.
Toxin(s) Oxalates. May also initiate histamine release in the body.
Toxic part(s) Probably the entire plant including the roots.
Signs Pain and swelling of the oral cavity. Acute inflammation of the oropharynx accompanied by salivation, pawing at the mouth, and drooling. Edema of the lips, tongue, and throat may be seen.
Treatment Usually none required. Rinse the mouth copiously with water or milk. Give the animal milk or other source of calcium. The calcium may precipitate soluble oxalates. Antihistamines may be helpful. Analgesics may be required. Swelling may be treated with cool compresses. It is unknown if diuretics or glucocorticosteroid would help with the inflarnmation. Rarely, swelling of the tongue, glottis, or pharynx will interfere with respiration. If necessary, secure the airway