Amornchai Somjetlertcharoen
Aquatic Animal Health Research Institute, Bangkok 10900 Thailand
Chloramphenicol, a protein synthesis inhibitor, is an antibiotic produced by Streptomyces venezuelae, an organism first isolated in 1947 from a soil sample collected in Venezuela. Chloramphenicol acts primarily by binding reversibly to the 50S ribosomal subunit and also can inhibit mitochondrial protein synthesis in mammalian cells. This drug is reserved for serious infections in which the location of the infection, susceptibility of the pathogen or poor response to other therapy indicate restricted antimicrobial option such as meningitis, typhus, and typhoid fever, who cannot take safer alternatives because of resistance or allergies. In addition, it used for treatment of rickettsial diseases in the patients who sensitized to tetracyclines and in those with reduced renal function in pregnant women.
|
|
There is limited evidence for carcinogenicity of chloramphenicol in humans. The most important adverse effects of chloramphenicol involve the haematopoietic system, possible idiosyncratic bone marrow suppression that presented as anemia, leukopenia, or thrombocytopenia, and potentially fatal toxicity to neonates exposed to excessive dose of chloramphenicol, called gray baby syndrome. Another haematological side effect is rare, unpredictable, non-dose-related aplastic anaemia, which often appears after drug has been discontinued. Chloramphenicol induces aplastic anemia, and this condition is related to the occurrence of leukemia. Other adverse effects include hypersensitivity reactions (macular or vesicular skin rashes), gastrointestinal complaints and neurological complication after long-term treatment. The structural feature of chloramphenical that is responsible for aplastic anemia is hypothesized to be the nitro group, which might be metabolized by intestinal bacteria to a toxic intermediate. However, the exact biochemical mechanism has not yet been elucidated.
 Florfenicol
|
In Asia, chloramphenicol has been widely used as a veterinarian antibiotic in aquaculture despite regal controls in many countries. Florfenicol and thiamphenicol, derivatives of chloramphenicol, are also used for treatment of bacterial infection. After finding of chloramphenicol residues in shrimp products exported from Asia to EU on September, 2001, the use of this drug in aquaculture is taken into account very seriously. According to USFDA, chloramphenicol, both animal and human drug, is placed in the list of substances those are prohibited for extra-label uses in all food-producing animals. The current list of prohibited drugs also includes furazolidone and nitrofurazone. From the EU food safety, chloramphenicol is located in the list of pharmacology active substances for which no maximum levels can be fixed. No drug
residual allowance to be found in food animals. The alternatives have been proposed to avoid using antimicrobials or other chemicals in food fish. Nutritional supplements and immunostimulants are considered to replace the using of drugs and chemicals by keeping the aquatic animals healthy till harvesting. Biocontrol, by using appropriate microbes, is an option to eliminate nitrogenous waste at the bottom of the ponds.
