Antibiotics, including penicillin are often taken when an infection is present or sometimes, to prevent an infection from occurring when undergoing a surgical procedure.
When seeing someone taking penicillin, they often assume its for an infection, as perfect princess mentioned. As to what kind of infection, it will vary depending on symptoms shown.
To add to what the other posters said, there are some times that a patient is asked to take antibiotics in preparation for an invasive procedure like a surgery or root canal treatment. It doesn't mean you have an infection at the time the drug was prescribed but as a preventive measure against possible infection while the treatment is being done.
This "prophylactic antibiotic regimen" is usually done for people with particular medical problems. But even healthy people with strong immune systems may occasionally be given preventive antibiotics—if they are having certain kinds of surgery that carry a high risk of infection, or if they are traveling to parts of the world where they are likely to get an infection that causes diarrhea, for example.
Linear Mode
