Why does penicillin attach to protein molecules in the body in some people while in others it doesn't?

[College Student]

Proteins in the blood can bind to penicillin (the hapten) and produce an allergic reaction by triggering an immune response. Why does this only happen in some people and not in all?

[ladypam]

There are a lot of reasons why people have various reactions to medications especially antibiotics like penicillin. A probable reason for this is the genetic configuration of the cells in the body. Each has their own genetic map and this dictates how it will react with certain substances. There are even times that the body recognizes its own cells as enemies such as in auto immune diseases.

Another possibility is the chemical structure of penicillin that contains a beta lactam ring as its functional group and which is responsible in attaching itself to proteins, normally of bacteria, but possibly with protein molecules in the blood to produce an allergic reaction. Hope this helps.