Can antibiotic use cause complication in mono patients?

Possibly: For the mono patients i see as an ENT doctor i usually prescribe steroids and an antibiotic. The patients usually have huge infected tonsils and i treat with antibiotics to prevent bacterial superinfection of the virally damaged tissue. In my years of experience this has been successful in not only helping the throat symptoms but preventing later secondary recurrent tonsillitis.

Yes: Specifically Amoxicillin causes a fairly characteristic rash.