Complex sentence: Since probenecid reduces the excretion of penicillin from the body, it increases the concentration of penicillin in the body and allows individuals to take less penicillin over a course of therapy.
Split into simpler sentences: Since probenecid reduces the excretion of penicillin from the body, a dose of penicillin will stay around the body for a longer period of time when taken with probenecid. Hence, probenecid allows individuals to take less penicillin over a course of therapy.