I want to let you know that while dogs can take antibiotics, they may not be as effective for a tooth abscess as other treatment methods. You can read about this here:
We are also not able to tell a client that we do not have an in-person relationship with that they should give a prescription medication. I can give you a site that gives you the usage, precautions, side effects and dosages for the various medications. Most dogs will have some stomach issues with antibiotics and as a result many recommend giving with food to help ease that side effect. Amoxicillin is a common choice.
You can read about amoxicillin here:
Read about Cipro on this page:
Levofloxacin is not one I'd use in an elderly dog due to side effects.
The problem you have with tooth abscesses is that the infection can spread throughout the body and affect other areas of your dog and even lead to organ failure. With him being an elderly dog already, this may be a serious issue. If at all possible, I'd try to get him into see your vet or another option is to have a mobile vet come by and at least check him over. You can find a mobile vet on the following page. Just put your zip code into the house call vet area and how far away you think a vet might come and press the search button. Mobile vet services have become pretty common across the country and that might be a better choice for your dog.
I hope this information is helpful to you. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have . If you do find this helpful, please take this opportunity to rate my answer positively so I am compensated for my time.