[Steve G]

Originally Posted by Jeff

The difference between ampicillin and amoxicillin is mainly one of licencing - as the patent on qds Penbritin (ampicillin) came too an end the new wonder antibiotic Amoxil was introduced with a tds dosage.

Amoxicillin half life 61.3 minutes
http://en.wikipedia.org/wiki/Amoxicillin

Ampicillin half life approx 1 hour
http://en.wikipedia.org/wiki/Ampicillin

Jeff

But half life is only part of the story, bioavailabilty is also important (95% for amoxicillin against 40% for ampicillin), as is volume of distribution and minimum inhibitory concentration.

Surely the licencing wouldn't be different unless there was a good reason for it, and given that amoxicillin is effective at a tds dose, why give it qds?