DOC for prophylaxis against Diphtheria is:-

Erythromycin is macrolide group of drug which binds irreversibly to a site on the 50s subunit of bacterial ribosome thus inhibiting translocation steps of protein synthesis. It is used to eliminate the carrier state of Corynebacterium Diphtheriae. Rifampicin: Blocks RNA transcription by interacting with B subunit of mycobacterial DNA dependent RNA polymerase.