Hi.. Thanks for the query. If Clindamycin is not working then he can consult his Dentist again so that he can advise Augmentin [Amoxicillin + Clavulanate Potassium] that is more appropriate for tooth abscess as compared to Azithromycin.. But many a times if there is an abscess, taking antibiotics will not solve the problem alone and the tooth will also need treatment for complete eradication of infection.. So my suggestion is that you should consult a Dentist and along with getting antibiotics, you should also get an x ray of his tooth done.. If tooth can still be saved with treatment then Pulpectomy can be done. If the tooth is deeply decayed extraction is advised so that the infection can completely subside. As you have not mentioned his age, for pain relief you should give him painkillers only after consulting an Emergency doctor/ dentist. Hope this helps.. Regards.