My Father Has A Very Bad Infection From Breaking The

my father has a very bad infection from breaking the root nerve on his front tooth. he was started on a z pak by the doctor but the dentist then put him on clindamycin 300mg. however the clindamycin is NOT working. is it safe to mix the two antibiotics to get the infection down faster, as his face is swollen so far the skin is stretched n i honestly feel his skin will split if the swelling does not stop.