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 occurring pencillin G and a semi-synthetic version, ampicillin. I circled the portion that differs between these two 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.
Other articles in this series:
1. A primer on antibiotic resistance: an introduction to the question of antibiotic resistance.
2. Natural vs. synthetic drugs: what is the difference between an antibiotics and synthetic drugs?
3. How do antibiotics kill bacteria? a general discussion of the pathways where antibiotics can act and one characteristic that helps some bacteria survive.
4. Are antibiotics really only made by bacteria and fungi? It depends on what you'd like to call them.
5. The Five paths to antibiotic resistance: a quick summary