CHLORAMPHENICOL (Veterinary—Systemic) Some commonly used brand names are: or moderately acid solutions. Its alcohol solution is For veterinary-labeled products—Chlor 250; Chlor 500; Chlor dextrorotatory and its ethyl acetate solution is levorotatory. 1000; Chloromycetin; Chlor Palm 125; Chlor Palm 250; Chloramphenicol Palmitate USP—Fine, white, unctuous, Duricol; Karomycin Palmitate 125; Karomycin Palmitate crystalline powder, having a faint odor. 250; and Viceton. Chloramphenicol Sodium Succinate USP—Light yellow powder. For human-labeled products—Chloromycetin and Novochlorocap. Solubility:{R-10} Chloramphenicol USP—Slightly soluble in water; freely soluble Note: For a listing of dosage forms and brand names by country in alcohol, in propylene glycol, in acetone, and in ethyl availability, see the Dosage Forms section(s). acetate. Chloramphenicol Palmitate USP—Insoluble in water; freely Category: Antibacterial (systemic). soluble in acetone and in chloroform; soluble in ether; sparingly soluble in alcohol; very slightly soluble in solvent hexane. Indications Chloramphenicol Sodium Succinate USP—Freely soluble in ELUS EL Note: The text between and describes uses that are not included water and in alcohol. ELCAN EL in U.S. product labeling. Text between and describes uses that are not included in Canadian product labeling. Pharmacology/Pharmacokinetics The ELUS or ELCAN designation can signify a lack of product Note: See also Table 1. Pharmacokinetic Parameters at the end of this availability in the country indicated. See the Dosage Forms monograph. section of this monograph to confirm availability. Mechanism of action/Effect: Accepted Chloramphenicol is bacteriostatic. However, it may be Chloramphenicol is a broad-spectrum antibiotic shown to have bactericidal in high concentrations or when used against specific activity against a wide variety of organisms that are the highly susceptible organisms. causative agents of several disease conditions in domestic Chloramphenicol, which is lipid soluble, diffuses through the animals. Such organisms include staphylococci and streptococci; bacterial cell membrane and reversibly binds to the 50 S some gram-negative organisms, such as Bordetella subunit of the bacterial ribosomes where transfer of amino bronchiseptica, Escherichia coli, and Salmonella species; acids to growing peptide chains is prevented (perhaps by anaerobic bacteria; and rickettsiae.{R-11} The species treated with suppression of peptidyl transferase activity), thus inhibiting chloramphenicol include dogs, ELUScatsEL, and ELUS,CANhorses EL. peptide bond formation and subsequent protein synthesis. Regulatory Considerations Absorption: U.S.— Chloramphenicol is rapidly absorbed from the gastrointestinal Food and Drug Administration regulations ban tract after oral administration in many simple-stomach chloramphenicol from use in animals that are used for animals. food production. There are no safe residue levels, and no Cats—Chloramphenicol palmitate is not absorbed well after oral withdrawal times have been established. administration to fasted cats.{R-1; 2} Chloramphenicol Tablets USP are labeled for veterinary use only. Canada— Distribution: Chloramphenicol is prohibited from use in food-producing Chloramphenicol diffuses readily into all body tissues, but at animals by the Canadian Health Protection Branch. different concentrations. Highest concentrations are found in Chloramphenicol Tablets USP are labeled for veterinary use only. the liver and kidneys of dogs. The lungs, spleen, heart, and skeletal muscles contain Chemistry concentrations similar to that in the blood. Chloramphenicol Source: Originally derived from Streptomyces venezuelae.{R-8} reaches significant concentrations in the aqueous and vitreous Chemical name: humors of the eye. Within 3 to 4 hours after administration, Chloramphenicol—Acetamide, 2,2-dichloro-N-[2-hydroxy-1- the concentration in the cerebrospinal fluid reaches, on the (hydroxymethyl)-2-(4-nitrophenyl)ethyl]-, [R-(R*,R*)]-.{R-9} average, 50% of the concentration in the serum. The Chloramphenicol palmitate—Hexadecanoic acid, 2-[(2,2- percentage increases if there is inflammation of the meninges. dichloroacetyl)amino]-3-hydroxy-3-(4-nitrophenyl) propyl Chloramphenicol diffuses readily into milk and pleural and ascitic ester, [R-(R*,R*)]-.{R-9} fluids and crosses the placenta, attaining concentrations of Chloramphenicol sodium succinate—Butanedioic acid, mono[2- about 75% of that in maternal blood. [(2,2-dichloroacetyl)amino]-3-hydroxy-3-(4- nitrophenyl)propyl]ester, monosodium salt, [R-(R*,R*)]-.{R-9} Biotransformation: Chloramphenicol is rather rapidly metabolized, Molecular formula: mainly in the liver, by conjugation with glucuronic acid. {R-9} Chloramphenicol—C11H12Cl2N2O5. {R-9} Elimination: Approximately 55% of a single daily dose can be Chloramphenicol palmitate—C27H42Cl2N2O6. {R-9} recovered from the urine of a treated dog. A small fraction of this Chloramphenicol sodium succinate—C15H15Cl2N2NaO8. Molecular weight: is in the form of unchanged chloramphenicol. The unchanged Chloramphenicol—323.13.{R-9} chloramphenicol is excreted by glomerular filtration (5 to 10%), Chloramphenicol palmitate—561.54.{R-9} whereas 80% is excreted via tubular secretion as inactive Chloramphenicol sodium succinate—445.18.{R-9} metabolite. Description:{R-10} Chloramphenicol USP—Fine, white to grayish white or yellowish Precautions to Consider white, needle-like crystals or elongated plates. Its solutions Species sensitivity are practically neutral to litmus. Is reasonably stable in neutral Cats—Chloramphenicol should not be used in the cat for more than © 2007 The United States Pharmacopeial Convention All rights reserved 1 14 days because it can cause dose-related blood dyscrasias.{R-2} Those indicating need for medical attention The reported increased susceptibility of cats to development of All species blood dyscrasias relative to dogs or horses may be attributable to Anorexia; bone marrow suppression;{R-7} depression; diarrhea chloramphenicol’s significantly longer elimination half-life in the and vomiting{R-6} cat.{R-6} Note: Intermediate metabolites are thought to be responsible for the reversible bone marrow suppression seen in domestic Pediatrics animals. All species The effect is dose-dependent, often occurring with long-term In the fetus and neonate, the immature liver cannot conjugate therapy. chloramphenicol, and toxic concentrations of active drug accumulate. Human side/adverse effects{R-12} In addition to the above side/adverse effects reported in animals, the Dogs and cats following side/adverse effects have been reported in humans, and Sudden death has been reported in puppies and kittens receiving are included in the human monograph Chloramphenicol intravenous chloramphenicol. (Systemic) in USP DI Volume I; these side/adverse effects are intended for informational purposes only and may or may not be Drug interactions and/or related problems applicable to the use of chloramphenicol in the treatment of The following drug interactions and/or related problems have been animals: selected on the basis of their potential clinical significance Note: The hematologic toxicity of chloramphenicol can manifest (possible mechanism in parentheses where appropriate)—not itself in 1 of 2 ways—either as a reversible bone marrow necessarily inclusive (» = major clinical significance): depression or an idiosyncratic aplastic anemia. Bone marrow Note: Combinations containing any of the following medications, depression is dose-related and most commonly seen when depending on the amount present, may also interact with this serum concentrations of chloramphenicol exceed 25 medication. mcg/mL. Bone marrow changes are usually reversible when Digitalis glycosides chloramphenicol is discontinued. Aplastic anemia is an (chloramphenicol decreases the rate of elimination of digitalis idiosyncratic reaction that occurs in 1 of every 25,000 to glycosides, which may lead to their accumulation to toxic 40,000 courses of treatment. It is not related to dose or concentrations){R-3} duration of therapy. Most cases have been associated with Erythromycin oral chloramphenicol, and the onset of aplasia may not occur (erythromycin and chloramphenicol compete for the same until weeks or months after treatment with chloramphenicol ribosome; therefore, the 2 medications may antagonize each has been discontinued. other if used concurrently) Incidence less frequent Medications metabolized by the mixed function oxidase system, Blood dyscrasias; gastrointestinal reaction especially: Incidence rare Phenobarbital or Gray syndrome—in neonates only; hypersensitivity Primidone reactions; neurotoxic reactions; optic neuritis; peripheral (chloramphenicol irreversibly inhibits the hepatic microsomal neuritis enzymes of the cytochrome P450 complex, which may Note: Gray syndrome (or ‘‘gray baby syndrome’’) almost potentiate the effects of other medications that are always occurs in newborn infants treated with metabolized by this complex) inappropriately high doses of chloramphenicol. Pentobarbital Typically, the infant has been started on (pentobarbital-induced anesthesia in dogs can be significantly chloramphenicol within the first 48 hours of life; prolonged by concurrent administration of symptoms first appear after 3 to 4 days of continued chloramphenicol){R-4} treatment with high doses of chloramphenicol; and serum concentrations are high, often between 40 and Patient monitoring 200 mcg/mL. If detected early and chloramphenicol is The