Periodontitis and peri-implantitis are a consequence of alterations in the oral microbiome. Depending on the clinical findings, adjunctive antibiotic therapy is therefore necessary in certain cases. However, the composition of the subgingival microflora can vary greatly between individuals. The concentration of the individual marker bacteria also fluctuates considerably between patients. Adjunctive antibiotic therapy should always target the pathogens present specifically while sparing the beneficial flora. For targeted therapy, a microbiological analysis is therefore necessary before an antibiotic is prescribed.