If there is an infected cut on his foot I would strongly recommend you consider having him checked by your family veterinarian. In the meantime, this is what you can do:
1- In response to your question, yes, you can give him 1/2 (half) of the 500mg Penicillin V every 8 hours for the next 7-10 days. But, you need to stop him from licking
or it is not going to get better. Pick up an ecollar (cone) in your local pet store to stop him from licking/gnawing at affected area. It is best to leave the area uncovered. Until you pick the ecollar you can apply a light bandage but the bandage needs to be changed 2-3 times a day.
2- Pick up in your local pharmacy (CVS) "Hibiclens" antimicrobial soap. Wash affected area with this soap 2-3 times a day.
3- After washing affected area as above apply a topical antibiotic like neosporin or bacitracin. Do this 2-3 times a day for the next 7-10 days.
4- Follow up with your family veterinarian.
Hope the above helps, if you have additional questions I will be glad to answer them.