I'm sorry that your question wasn't answered in a timely manner. Red's vet has diagnosed stomatitis if he's suggesting total teeth extraction. This doesn't respond to penicillin - at least in any meaningful manner and so I recommend your not considering administering it. Here's my synopsis of stomatitis in cats for you:
Stomatitis presents a therapeutic challenge, and management is often frustrating for both me and owner. Many cases are refractory to treatment. A multimodal approach is imperative in patients with stomatitis, often requiring a combination of medical and surgical therapies for resolution of clinical signs and occasional placement of an esophageal feeding tube for nutritional management. Plaque control is achieved with professional dental cleaning, topical and systemic antimicrobial therapy, and tooth extraction. Systemic antibiotic therapy (e.g. , potentiated amoxicillin suspension) often provides only short-term clinical benefit or can be ineffective in the initial management of inflammation. Topical chlorhexidine (0.12%) products may be used for adjunctive therapy in the initial management.
Corticosteroids (injectable methylprednisolone , oral prednisolone, dexamethasone, or triamcinolone) are often required to decrease inflammation, reduce pain, and stimulate appetite. The presence of lymphocytes and plasmacytes in the tissues suggest an "up-regulation " (over-activity) of the immune system and so the immunosuppressive cyclosporin may be useful starting at 2.5 mg/kg of Neoral solution orally every 12 hours and given for 6 weeks before judging effectiveness. Low-dose doxycycline (an antibiotic with anti-inflammatory and immunomodulary effects) at 1mg/kg orally once daily and feline interferon omega (5 MU are diluted and divided as necessary to submucosally inject all inflamed areas; the remaining 5 MU are injected into a 100 mL bag of sodium chloride and frozen in ten 10 ml aliquots - you then give 1 mL orally every 24 hours for 100 days; the 10 mL fraction in use is refrigerated and the other aliquots are kept frozen until needed) have also been suggested as medical treatment options for cats with stomatitis.
When the above fail, tooth extraction appears to be the best long-term therapeutic strategy because it removes the surfaces that are available for plaque retention. Plaque seems to play a role in perpetuating stomatitis even if teeth are located relatively distant from the actual site of inflammation. Therefore reasonably healthy teeth may be extracted in cats with severe stomatitis that do not respond to medication. Extraction of all teeth caudal to the canine teeth is often sufficient. The response to tooth extraction ranges from complete resolution of inflammation (60%); minimal residual inflammation, and no oral pain (20%); to initial improvement requiring continued medical therapy to control clinical signs (13%); to no improvement (7%). Cats tolerate extractions, even full-mouth extractions, very well and can eat moist and even dry food without teeth. Laser surgery may be used as an adjunct in patients with refractory stomatitis not responding to extractions and medical therapy.One investigation found that 88% of cats with stomatitis were shedding both feline calicivirus and feline herpesvirus in saliva, suggesting that these two viruses play a role in feline stomatitis. Evidence for a cause-and-effect relationship between the bacteria Bartonella and feline stomatitis has not been provided. FeLV (leukemia virus) and FIV (kitty AIDS) have also been found in these cases and so hopefully Red has already been tested for those viruses.
Please respond with further questions or concerns if you wish.