Chloramphenicol is produced by an actinomycete, Streptomyces venezuelae, which was initially found in soil sample in Venezuela in 1947. The drug was successfully synthesized in 1948, large scale clinical trials were conducted with extraordinary expediency and the drug was marketed for general usage in 1949. Chloramphenicol was quickly recognized as an important addition to our therapeutic armamentarium, but this enthusiasm was quickly tempered by reports of serious blood dyscrasias noted as early as 1950. Chloramphenicol is a derivative of dichloracetic acid with a nitrobenzene moiety and a molecular weight of 324 daltons. The dichloracetamide side chain is critical for antimicrobial activity. The drug is extremely stable to temperature and pH changes; solubility is about 0.25 mg/ml in water and 400 mg/ml in alcohol. Thiamphenicol is a chloramphenicol derivative in which the nitro group of the benzene ring is replaced by a sulphomethyl group. This derivative is not available in the United States, but it has been used extensively in Europe, has demonstrable efficacy, and most interestingly, has not been clearly implicated in causing aplastic anemia.
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