I have tooth abcess and my dentist prescribed antibiotic for 4x a day on the 1st 3days and less it to 2x a day on the 4th to 7th day. Is that possible?

Yes it can be. . Although not knowing the name of the antibiotic still there are different ways different physicians prescribe antibiotics. Usually the medicines are prescribed two or four times because of the time they will remain in the system so if the remain in the body for Six hours they usually are prescribed four times a day. But sometimes due to severity of infection people use it more frequent initially .
Abcess/antibiotics. Antibiotics will only help control the symptoms of an abcess...they will not heal the abcess. The treatment needed for a tooth abcess is a root canal.
Possible. Possible regimen. Assuming your are improving. if no better after 48 hours, contact dentist for advice.