Chloramphenicol is a bacteriocidal antimicrobial. It is considered a prototypical broad-spectrum antibiotic, alongside the tetracyclines.
Chloramphenicol is effective against a wide variety of Gram-positive and Gram-negative bacteria, including most anaerobic organisms. Due to resistance and safety concerns, it is no longer a first-line agent for any indication in developed nations, although it is sometimes used topically for eye infections. Nevertheless, the global problem of advancing bacterial resistance to newer drugs has led to renewed interest in its use. In low-income countries, chloramphenicol is still widely used because it is inexpensive and readily available.
It was the first antibiotic to be manufactured synthetically on a large scale.
Despite safety concerns, chloramphenicol is, in many ways, an ideal antibiotic for the 17th century environment. It is effective against many of the major epidemic diseases of 17th century Europe. In particular, it is effective against plague and typhus, which are not affected by penicillin. However, it is not effective against diphtheria.
Just as importantly, it can be synthesized (at least in "bucket-shop" quantities) using available materials and equipment, and can be stockpiled for later use. Also, "Portraits" suggests that it can be made by down-time chemists, at least if detailed instructions are available. However, "Ounces Of Prevention" suggests that some of those details, such as the need for controlled near-freezing temperatures and very pure sulfuric and nitric acid, meant that it could take years to go from having detailed instructions for making chloramphenicol to actually developing the ability to produce it.