Tonsillitis / Pharyngitis - unable to swallow (if sepsis see treatment option here)

Benzylpenicillin IV 1.2g 6 hourly for 10 days (IV and oral)

If true penicillin / beta-lactam allergy:

Clarithromycin* IV 500mg 12 hourly for 5 days

If severe swallowing problems or suspected quinsy refer urgently to ENT. 

*Clarithromycin - serious drug interactions and risk of QT prolongation (see here for further information and  BNF Appendix 1).