How long does it take an antibiotic to leave your system?

Antibiotic Half-Life: The half-life of an antibiotic in the system varies greatly among antibiotic. Each antibiotic has it's own half-life which is the time it takes for half of the drug to leave the body. Normally, after 5 half-lives, the drug is considered totally gone. So if Ampicillin has a half life of 1 hour, after 5 hours it is completely gone from the body. Remember, each drug has it's own unique half life.