Why do you take an antibiotic before surgery?

Antibiotics are not necessary for every operation. It is given when emergency Surgery is carried out due to trauma, in presence of infection, in patients with valvular Heart disease to prevent bacterial endocarditis, and in operations where prosthesis is used like in Joint replacement surgery, mesh repair of hernias, and in immuno compromised patients. The role of antibiotics is to prevent infection, as prosthesis are foreign bodies and once infected, it may have to be removed.