Antibacterials (ABX) Practice Exam

Absorption from the gut is all about how much and how quickly the drug enters the bloodstream after an oral dose. Amoxicillin is more rapidly absorbed because it’s more stable in stomach acid and has higher oral bioavailability. In numbers, amoxicillin around 75% of an oral dose reaches systemic circulation, whereas ampicillin is only about 40–50%. That means amoxicillin achieves higher and faster plasma levels when given by mouth, while ampicillin is absorbed less efficiently due to being more acid-labile. If the drug is given by IV, both bypass this step, but for oral dosing the difference in absorption makes amoxicillin the faster-absorbing option.