Friend, it sounds like his paw is very irritated and this could be the reason why he is limping. It is important to stop him from licking or he will not let it heal and even make it worst. This is what you can try:
1- Need to stop him from licking or he is going to delay healing. Pick up an ecollar (cone) in your local pet store to stop him from licking/gnawing at affected paw.
2- Pick up in your local pharmacy "Hibiclens" antimicrobial soap or chlorhexiderm scrub. Dilute 1-2 tablespoon for every cup of water. Use this mixture to soak the paw for a few minutes 2-3 times a day. You can also just wash the paw with this soap; whatever is easier for you. Once he has the ecollar on it will be easier to touch the paw. Just have another person helping you.
3- After soaking or washing affected paw as above apply a topical antibiotic like neosporin or bacitracin. Do this 2-3 times a day for the next 7-10 days.
4- Buffered Aspirin 325mg every 12 hours for 1 week. You can buy buffered aspirin over the counter in any pharmacy (chemist).
5- If no significant improvement after doing the above for 2-3 days follow up with your family veterinarian for a hands on examination.
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