What's the difference between a synthetic drug and an antibiotic?
Sometimes there's no difference at all.
Let's take a look at chloramphenicol and couple of pencillins.
Chloramphenicol kills many different kinds of bacteria by interfering with their ability to make new proteins. Here's a point where language gets tricky. Originally, chloramphenicol was isolated and purified from Streptomyces (a kind of bacteria). But, chloramphenicol is small and chemists are able to synthesize it. So even though we consider antibiotics to be natural products, they don't have to be made in a "natural" way.
Some antibiotics are also made by bacteria and then modified further through synthetic chemistry. These chemical modifications are used to make the antibiotic a better drug. Some examples are modifications that antibiotics withstand stomach acids; others can make antibiotics more resistant to bacterial enzymes. Many different antibiotics have been produced by modifying penicillin. Here we have a naturally occuring pencillin G and a semi-synthetic version, ampicillin. I circled the portion that is shared by both molecules. I probably owe my life to penicillin since one of my earliest childhood memories is a stay in the hospital when I was sick with pneumonia.
Read the intro and get a clue about upcoming topics.