How long does antibiotics last in the blood stream?

Answer 1

Most of the antibiotics last for very short time in your blood. They have different half lives. The half life of penicillin is say half an hour. That of ampicillin is is about 90 minutes. That of amoxycillin is about 60 minutes. You need not maintain the blood level of the antibiotic. The so called post antibiotic effect take care of the infection. The ceftriaxone has got half life of about 10 hours. So once a day dose can be enough in most cases. The benzathine penicillin has got very long half life and once a month or once in three weeks dose will prevent the streptococcal infection.

Answer 2

Each antibiotic has a different life time, an antibiotic could be administer every 4,6, 8, 12 o 24 hours.