Actually if the drug did not work,probably bad guys that make your tooth hurt are already resistant to it.
As far as i know , amoxicillin is almost always first line in these infections because: it is cheap, it usually works, it has relatively subtle side
effects. Clindamycin is totally different family. Not given as first line because side effects (rare ones, but sometimes problematic) and because
increasing resistance to it is not wise. As for second time - do not know what is novo-penicillin, maybe penicillin v? Can not see reason why if it is
so, but not a doctor.
Anyway, these drugs are cheap (relatively) so his shares would not go up very much.

However in costly treatments immoral person could play these
tricks. But this is a minority of doctors, i suppose (or hope...).