Chloramphenicol

Absorption

Rapidly and completely absorbed from gastrointestinal tract following oral administration (bioavailability 80%). Well absorbed following intramuscular administration (bioavailability 70%). Intraocular and some systemic absorption also occurs after topical application to the eye.

Toxicity

Oral, mouse: LD50 = 1500 mg/kg; Oral, rat: LD50 = 2500 mg/kg. Toxic reactions including fatalities have occurred in the premature and newborn; the signs and symptoms associated with these reactions have been referred to as the gray syndrome. Symptoms include (in order of appearance) abdominal distension with or without emesis, progressive pallid cyanosis, vasomotor collapse frequently accompanied by irregular respiration, and death within a few hours of onset of these symptoms.

Description

Chloramphenicol was originally produced by fermentation of Streptomyces venezuelae, but its comparatively simple chemical structure soon resulted in several efficient total chemical syntheses. With two asymmetric centers, it is one of four diastereomers, only one of which (1R,2R) is significantly active. Because total synthesis produces a mixture of all four, the unwanted isomers must be removed before use. Chloramphenicol is a neutral substance that is only moderately soluble in water, because both nitrogen atoms are nonbasic under physiologic conditions (one is an amide and the other a nitro moiety). It was the first broad-spectrum oral antibiotic used in the United States and was once very popular. Severe potential blood dyscrasia has greatly decreased its use in North America. Although its cheapness and efficiency makes it still very popular in much of the rest of the world where it can often be purchased over-the-counter without a prescription

Description

Chloramphenicol is a venerable antibiotic that was isolated from the soil bacterium Streptomyces venezuelae in the late 1940s by researchers at Parke–Davis (Detroit), the University of Illinois (Urbana–Champaign), and Yale University (New Haven, CT). It was originally called chloromycetin.
In July 1949, the Parke–Davis team published the structure of the compound, which then was given the generic name chloramphenicol; Parke–Davis adopted Chloromycetin as its trade name. The group simultaneously announced a laboratory synthesis of chloramphenicol. It was the first totally synthetic antibiotic.
Over the years, chloramphenicol has been used to treat conjunctivitis, meningitis, cholera, and typhoid fever. It is active against bacteria such as Escherichia coli, Staphylococcus spp., and Salmonella spp.
Chloramphenicol can produce some serious adverse effects, including aplastic anemia, neurotoxicity, and some cancers. In 1991, the United States discontinued the use of the oral formulation because of its association with aplastic anemia. In 2007, the World Health Organization classified it as a probable human carcinogen.
Chloramphenicol is still being used in the United States and other countries as an injectable. It is administered intravenously as the more water-soluble prodrug chloramphenicol monosuccinate. Intravenous dosages are greater than oral ones because much of the ester is eliminated before the body can hydrolyze it. Another prodrug, chloramphenicol palmitate, is given orally, but like the parent compound, it is no longer approved for use in the United States.

Chemical properties

White to grey-white crystalline powder

Chemical properties

Chloramphenicol is a white to grayish-white or yellowish-white crystalline solid.

Originator

Leukomycin,Bayer,W. Germany

The Uses of Chloramphenicol

Chloramphenicol is unusual nitroaromatic metabolite produced by Streptomyces venezuelae, first published in 1947. Chloramphenicol is a broad spectrum antibiotic with good activity against Gram negative and anaerobic bacteria. Although restricted to ocular use, antibiotic resistance to other classes has refocused attention on this class. Chloramphenicol acts by binding to the 23S sub-unit of the 50S ribosome, inhibiting protein synthesis. Chloramphenicol has been extensively studied with over 35,000 literature citations.
Chloramphenicol is a protein translation blocking antibiotic.

The Uses of Chloramphenicol

Broad spectrum antibiotic obtained from cultures of the soil bacterium Streptomyces venezuelae. It has a broad spectrum of activity against Gram-positive and gram-negative bacteria. Antibacterial; antirickettsial

The Uses of Chloramphenicol

antibacterial, antirickettsial, inhibits protein synthesis

Indications

Used in treatment of cholera, as it destroys the vibrios and decreases the diarrhea. It is effective against tetracycline-resistant vibrios. It is also used in eye drops or ointment to treat bacterial conjunctivitis.

Background

An antibiotic first isolated from cultures of Streptomyces venequelae in 1947 but now produced synthetically. It has a relatively simple structure and was the first broad-spectrum antibiotic to be discovered. It acts by interfering with bacterial protein synthesis and is mainly bacteriostatic. (From Martindale, The Extra Pharmacopoeia, 29th ed, p106)
The FDA has withdrawn all oral drug products containing chloramphenicol, due to the high risk of fatal aplastic anemia associated with this specific route of administration.

Definition

ChEBI: Chloramphenicol is an organochlorine compound that is dichloro-substituted acetamide containing a nitrobenzene ring, an amide bond and two alcohol functions. It has a role as an antimicrobial agent, an antibacterial drug, a protein synthesis inhibitor, an Escherichia coli metabolite, a Mycoplasma genitalium metabolite and a geroprotector. It is an organochlorine compound, a diol, a C-nitro compound and a carboxamide.

Indications

Resistance to chloramphenicol is usually explained by the presence of a plasmid that determines the production of chloramphenicol acetyltransferase. This enzyme acetylates the drug, giving it unable to bind with 50 S subunits of bacterial ribosomes.
Chloramphenicol is a potentially toxic drug and has a few indications for use. It is the drug of choice for treating typhoid fever, and it is used for treating brain abscesses. Until recently, it was the drug of choice for therapy of bacterial meningitis in children (in combination with ampicillin). However, third-generation cephalosporins are currently preferred for such purposes. Chloramphenicol is an effective alternative for a number of infections in situations, where drugs of choice cannot be used for one reason or another. However, it should never be used for infections that can readily be treated with other antimicrobial drugs. Synonyms of this drug are levomycetin, amindan, aquamycetin, chloromycetin, ophthoclor, opulets, leukomycin, and many others.

Manufacturing Process

Chloramphenicol may be prepared by fermentation or by chemical synthesis. The fermentation route to chloramphenicol is described in US Patents 2,483,871 and 2,483,892. To quote from US Patent 2,483,892: The cultivation of Streptomyces venezuelae may be carried out in a number of different ways. For example, the microorganism may be cultivated under aerobic conditions on the surface of the medium, or it may be cultivated beneath the surface of the medium, i.e., in the submerged condition, if oxygen is simultaneously supplied.
Briefly stated, the production of chloramphenicol by the surface culture method involves inoculating a shallow layer, usually less than about 2 cm, of a sterile, aqueous nutrient medium with Streptomyces venezuelae and incubating the mixture under aerobic conditions at a temperature between about 20° and 40°C, preferably at room temperature (about 25°C), for a period of about 10 to 15 days. The mycelium is then removed from the liquid and the culture liquid is then treated by methods described for isolating therefrom the desired chloramphenicol. The synthetic route to chloramphenicol is described in US Patent 2,483,884 as follows: 1.1 g of sodium is dissolved in 20 cc of methanol and the resulting solution added to a solution of 5 g of benzaldehyde and 4.5 g of betanitroethanol in 20 cc of methanol. After standing at room temperature for a short time the gel which forms on the mixing of the reactants changes to a white insoluble powder. The precipitate is collected, washed with methanol and ether and then dried. The product thus produced is the sodium salt of 1- phenyl-2-nitropropane-1,3-diol.
Eighteen grams of the sodium salt of 1-phenyl-2-nitropropane-1,3-diolis dissolved in 200 cc of glacial acetic acid. 0.75 g of palladium oxide hydrogenation catalyst is added and the mixture shaken at room temperature under three atmospheres pressure of hydrogen overnight. The reaction vessel is opened, 2.5 g of 10% palladium on carbon hydrogenation catalyst added and the mixture shaken under three atmospheres pressure of hydrogen for 3 hours. The catalyst is removed from the reaction mixture by filtration and the filtrate concentrated under reduced pressure. Fifty cubic centimeters of npropanol is added to the residue and the insoluble inorganic salt removed by filtration.
The filtrate is treated with excess hydrochloric acid and evaporated to obtain a pale yellow oil. Five grams of the oil thus obtained is treated with 15 cc of saturated potassium carbonate solution and the mixture extracted with 50 cc of ether, then with 30 cc of ethyl acetate and finally with two 30 cc portions of ethanol. Evaporation of the solvent from the extract gives the following quantities of the desired 1-phenyl-2-aminopropane-1,3-diol: 0.5 g, 1.0 g and 3.1 g.
1.7 g of 1-phenyl-2-aminopropane-1,3-diol is treated with 1.6 g of methyl dichloroacetate and the mixture heated at 100°C for 1.25 hours. The residue is washed with two 20 cc portions of petroleum ether and the insoluble product collected. Recrystallization from ethyl acetate yields the desired (dl)- reg.-1-phenyl-2-dichloroacetamidopropane-1,3-diol in pure form; MP 154° to 156°C.Five hundred milligrams of (dl)-reg.-1-phenyl-2-dichloroacetamidopropane- 1,3-diolis added to a solution consisting of 1 cc of pyridine and 1 cc of acetic anhydride and the resulting reaction mixture heated at 100°C for 1/2 hour. The reaction mixture is evaporated to dryness under reduced pressure and the residue taken up in and crystallized from methanol. Recrystallization from methanol produces the pure diacetate of (dl)-reg.-1-phenyl-2-dichloroacetamidopropane-1,3-diol (MP 94°C). Two hundred milligrams of the diacetate of (dl)-reg.-1-phenyl-2- dichloroacetamidopropane1,3-diol is added to a mixture consisting of 0.25 cc of concentrated nitric acid and 0.25 cc of concentrated sulfuric acid at 0°C. The reaction mixture is stirred until solution is complete, poured onto 25 g of ice and the mixture extracted with ethyl acetate. The ethyl acetate extracts are evaporated under reduced pressure and the diacetate of (dl)-reg.-1- pnitrophenyl-2-dichloroacetamidopropane-1,3-diol so produced purified by recristallization from ethanol; MP 134°C.
Five hundred milligrams of the diacetate of (dl)-reg.-1-p-nitrophenyl-2- dichloroacetamidopropane-1,3-diol is dissolved in a mixture consisting of 25 cc of acetone and an equal volume of 0.2 N sodium hydroxide solution at 0°C and the mixture allowed to stand for one hour. The reaction mixture is neutralized with hydrochloric acid and evaporated under reduced pressure to dryness. The residue is extracted with several portions of hot ethylene dichloride, the extracts concentrated and then cooled to obtain the crystalline (dl)-reg.-1- p-nitrophenyl-2-dichloroacetamidopropane-1,3-diol; MP 171°C.

brand name

Chloromycetin (Parke-Davis);Acne-sol;Acnoxin;Actimac;Actinac;Alficetyn susp.;Altabactin;Ambrasynth;Amphemycin-prednisonum;Ampliomicetin;Amseclim;Angimidone;Angiters;Antibiopto;Aquapred;Armacol;Arrlicetin;Aviatrin;Balkamycin;B-cpct;Bemacol;Berlicetin;Biofeniol;Biophtas;Biotocap;Bismophenyl;Bitencyl;C. o fluo-fenicol;C. o hidrocor-clora;Cafenolo;Calmina;Campiol;Caosol;Cavumycetina;Ccombinado balsamico;Ccorticol;Cebenicol;Chemibal;Chemyzin;Chloramfenicol;Chloramol;Chloramphenicol intervetra;Chloramphenicol-pos;Chloramphycin;Chloramplast;Chloramson;Chloranfeni-mck;Chloranfeni-opipno;Chloranfeni-otico;Chloranfeni-ungena;Chloreptic;Chlorical;Chloroantibion;Chlorocortal;Chlorofair;Chloroject s;Chloromex;Chloromik;Chloromimyxin;Chloromycetin kapseals;Chloromycetin palmitate;Chloroptic p. oint.;Chlorostrep;Clorbiotina;Clorbis supp.;Cloromicetin;Cloromycetin;Cloroptic farmicetina;Clorosyntex;Colidene;Colimy-c;Cortican;Cortidermale;Cortimisin;Cortiphenicol;Cortison-quemicet;Cortivert;Cutispray no. 4;Cyphenicol;Cysticat;Davuron sedante;Dectamicina;Delta optil;Devamycetin;Dexa-biofinicol;Dorsec;Duphenicol;Econoclor;Ejificol strept;Ejificol sulfa;Elase chloromycel;Enttocetrin;Erittronicol;Erteilen;Esterofenil;Estevecicina cloranfenico;Extracicilina;Fago-praxin;Fluorobioptal;Furacol l;Furamecetil alpha magna;Furamecetil magna;Furatrimon;Furokatin;Gammaphenicol;Ginetris;Gino-dectacil;Gliscol;Globveticol;Goticas;Nova-phenicol;Novoclorocap;Oftan;Ophthaphenicol;Opthalon;Oralmisetin;Otiprin;Otopred ear drops;Pantofenicol;Parcyclin;Pedimycetin;Pentocetina;Pertaril;Pimabiciron;Pinimentac;Plastoderma;Prednomycetine;Procusulf;Protercicline;Prurivet;Pulmo vinco;Quitrase antibiotico;Ranphenicol;Ranstrepcol;Reclor;Redidropsol;Renegen;Reocetin;Reostop;Rheofin;Rivomycin sulfa;Rolintrex;Roncovita;Ronphenil;Roscomycin;Rovictor;Samaphenicol;Scanicoline;Scieramycetin;Sergo-amigdalar;Serviclofen;Sigmicilina;Sintomitsin;Snophenicol;Soludectancil;Sopamycetin;Spasmo-paraxin;Spersanicol;Strepticine;Streptoglobenicol;Streptophenicol;Subital supp.;Suismycetin;Sulfaglobenicol;Sulfamycetin;Synthomycetina;Synthophtone;Tardomyocel;Tega-cetin;Tetrachlorasone;Tetracol;Tetranfen;Tetraphenicol;Tetra-phenicol oculos;Tiframilk;Tiromycetin;Toramin;Transicetina;Transpulmycin;Tribiotic;Trophen;Troymycetin;Tusolone;Tycloran;Uro-gliscal 500;Uroletten-s;Uroplex 4;Ut forte;Uvomycin;Variolan;V-crayolan;Vetical;Vetophenicol;Viceton;Viklorin;Virogin;Vitaklorin;Vsmpozim;Wintetil;Zoppib spray blu;Gotimycetin;Ichthoseptal;Iruxolum;Isicetina;Isopto fenicol;Kavipe;Kloramfex.

Therapeutic Function

Antimicrobial

World Health Organization (WHO)

Chloramphenicol, an antibiotic isolated from Streptomyces venezuelae in 1947, first became available for general clinical use in 1948. By 1950 it was evident that its use could cause serious, sometimes fatal, blood dyscrasias. However, it remains one of the most effective antibiotics for treating invasive typhoid fever and salmonellosis, some rickettsioses and serious infections caused by Haemophilus influenzae or anaerobic organisms. This is considered to justify its retention in the WHO Model List of Essential Drugs. (Reference: (WHTAC1) The Use of Essential Drugs, 2nd Report of the WHO Expert Committee, 722, , 1985)

Antimicrobial activity

It is active against a very wide range of organisms. Minimum inhibitory concentrations (MICs) (mg/L) for other organisms are: Staphylococcus epidermidis, 1–8; Corynebacterium diphtheriae, 0.5–2; Bacillus anthracis, 1–4; Clostridium perfringens, 2–8; Mycobacterium tuberculosis, 8–32; Legionella pneumophila, 0.5–1; Bordetella pertussis, 0.25–4; Brucella abortus, 1–4; Campylobacter fetus, 2–4; Pasteurella spp., 0.25–4; Serratia marcescens, 2–8; Burkholderia pseudomallei, 4–8. Most Gramnegative bacilli are susceptible, but Pseudomonas aeruginosa is resistant. Leptospira spp., Treponema pallidum, chlamydiae, mycoplasmas and rickettsiae are all susceptible, but Nocardia spp. are resistant. It is widely active against anaerobes, including Actinomyces israelii (MIC 1–4 mg/L), Peptostreptococcus spp. (MIC 0.1–8 mg/L), and Fusobacterium spp. (MIC 0.5–2 mg/L), but Bacteroides fragilis is only moderately susceptible (MIC about 8 mg/L).
It is strictly bacteristatic against almost all bacterial species, but exerts a bactericidal effect at 2–4 times the MIC against some strains of Gram-positive cocci, Haemophilus influenzae and Neisseria spp. The minimum bactericidal concentrations (MBCs) for penicillin-resistant pneumococci are often significantly higher than those for penicillin- susceptible strains, although this cannot be detected by conventional disk susceptibility testing or MIC determination. Its bacteristatic effect may inhibit the action of penicillins and other β-lactam antibiotics against Klebsiella pneumoniae and other enterobacteria in vitro, but the clinical significance of this is doubtful. The presence of ampicillin does not affect the bactericidal effect of chloramphenicol on H. influenzae.

Acquired resistance

The prevalence of resistant strains in many Gram-positive and Gram-negative organisms reflects usage of the antibiotic. Over-the-counter sales are believed to have compounded the problem in some countries. For example, it has long been the drug of choice for the treatment of typhoid and paratyphoid fevers, but widespread use led to a high prevalence of resistant Salmonella enterica serotype Typhi. Outbreaks of infection caused by chloramphenicol-resistant S. Typhi have been seen since the early 1970s. Use of co-trimoxazole and fluoroquinolones in typhoid has resulted in a decline in chloramphenicol resistance in some endemic areas. Many hospital outbreaks caused by multiresistant strains of enterobacteria, notably Enterobacter, Klebsiella and Serratia spp., have been described.
Plasmid-borne resistance was first noted in shigellae in Japan and subsequently spread widely in Central America, where it was responsible for a huge outbreak. Strains of S. Typhi resistant to many antibiotics including chloramphenicol are particularly common in the Indian subcontinent. Resistance in shigellae is also relatively common in some parts of the world.
Resistant strains of H. influenzae (some also resistant to ampicillin), Staph. aureus and Streptococcus pyogenes are also encountered. Most N. meningitidis strains remain susceptible,but high-level resistance (MIC >64 mg/L) due to the production of chloramphenicol acetyltransferase has been described; the nucleotide sequence of the resistance gene was indistinguishable from that found on a transposon in Cl. perfringens. Resistant strains of Enterococcus faecalis are relatively common, and resistance to chloramphenicol is found in some multiresistant pneumococci.
Resistance in Staph. aureus is caused by an inducible acetyltransferase; additionally, the cfr (chloramphenicol– florfenicol resistance) gene encodes a 23S rRNA methyltransferase that also confers resistance to linezolid. In Escherichia coli, the capacity to acetylate chloramphenicol (at least three enzymes are involved) is carried by R factors. Replacement of the 3-OH group, which is the target of acetylation, accounts for the activity of fluorinated analogs against strains resistant to chloramphenicol and thiamphenicol. The resistance of B. fragilis and some strains of H. influenzae is also due to elaboration of a plasmid-encoded acetylating enzyme; in others it is due to reduced permeability resulting from loss of an outer membrane protein. Some resistant bacteria reduce the nitro group or hydrolyze the amide linkage. Resistance of Ps. aeruginosa is partly enzymic and partly due to impermeability.

General Description

Synthetic bacteriostatic antibiotic that inhibits the translation of RNA by blocking the peptidyltransferase reaction on ribosomes.

Hazard

Has deleterious and dangerous side effects. Must conform to FDA labeling requirements. Use is closely restricted. Probable carcinogen.

Contact allergens

This broad spectrum phenicol group antibiotic has been implicated in allergic contact dermatitis. Cross-sensitivity to thiamphenicol is possible, but not systematic.

Biochem/physiol Actions

Potency: ≥970 μg/mg

Mechanism of action

Chloramphenicol is bacteriostatic by virtue of inhibition of protein biosynthesis in both bacterial and, to a lesser extent, host ribosomes. Chloramphenicol binds to the 50S subparticle in a region near where the macrolides and lincosamides bind.
Resistance is mediated by several R-factor enzymes that catalyze acetylation of the secondary and, to some extent, the primary hydroxyl groups in the aliphatic side chain. These products no longer bind to the ribosomes and so are inactivated. Escherichi a coli frequently is resistant because of chloramphenicol's lack of intercellular accumulation.

Pharmacokinetics

Chloramphenicol is a broad-spectrum antibiotic that was derived from the bacterium Streptomyces venezuelae and is now produced synthetically. Chloramphenicol is effective against a wide variety of microorganisms, but due to serious side-effects (e.g., damage to the bone marrow, including aplastic anemia) in humans, it is usually reserved for the treatment of serious and life-threatening infections (e.g., typhoid fever). Chloramphenicol is bacteriostatic but may be bactericidal in high concentrations or when used against highly susceptible organisms. Chloramphenicol stops bacterial growth by binding to the bacterial ribosome (blocking peptidyl transferase) and inhibiting protein synthesis.

Pharmacokinetics

Oral absorption: 80–90%
C_max 500 mg oral: 10–13 mg/L after 1–2 h
Plasma half-life: 1.5–3.5 h
Volume of distribution: 0.25–2 L/kg
Plasma protein binding: c. 25–60%
Absorption
The plasma concentration achieved is proportional to the dose administered. Suspensions for oral administration to children contain chloramphenicol palmitate, a tasteless and bacteriologically inert compound, which is hydrolyzed in the gut to liberate chloramphenicol. Following a dose of 25 mg/kg, peak plasma levels around 6–12 mg/L are obtained, but there is much individual variation.
Pancreatic lipase is deficient in neonates and, because of poor hydrolysis, the palmitate should be avoided. In very young infants, deficient ability to form glucuronides, and low glomerular and tubular excretion greatly prolong the plasma half-life. For parenteral use, chloramphenicol sodium succinate, which is freely soluble and undergoes hydrolysis in the tissues with the liberation of chloramphenicol, can be injected intravenously or in small volumes intramuscularly. The plasma concentrations after administration by these routes are unpredictable, and approximate to only 30–70% of those obtained after the same dose by the oral route. Protein binding is reduced in cirrhotic patients and neonates, with correspondingly elevated concentrations of free drug.
Distribution
Free diffusion occurs into serous effusions. Penetration occurs into all parts of the eye, the therapeutic levels in the aqueous humor being obtained even after local application of 0.5% ophthalmic solution. Concentrations obtained in cerebrospinal fluid (CSF) in the absence of meningitis are 30–50% of those of the blood and greater in brain. It crosses the placenta into the fetal circulation and appears in breast milk.
Metabolism
It is largely inactivated in the liver by conjugation with glucuronic acid or by reduction to inactive arylamines; clearance of the drug in patients with impaired liver function is depressed in relation to the plasma bilirubin level. It has been suggested that genetically determined variance of hepatic glucuronyl transferase might determine the disposition and toxicity of the drug.
Excretion
It is excreted in the glomerular filtrate, and in the newborn elimination may be impaired by the concomitant administration of benzylpenicillin, which is handled early in life by the same route. Inactive derivatives are eliminated partly in the glomerular filtrate and partly by active tubular secretion. Over 24 h, 75–90% of the dose appears in the urine, 5–10% in biologically active forms and the rest as metabolites, chiefly as a glucuronide conjugate. Excretion diminishes linearly with renal function and at a creatinine clearance of <20 ml/min, maximum urinary concentrations are 10–20 mg/L rather than the 150–200 mg/L found in normal subjects. Because of metabolism, blood levels of active drug are only marginally elevated in renal failure, but microbiologically inactive metabolites accumulate. The plasma half-life of the products in the anuric patient is around 100 h, and little is removed by peritoneal or hemodialysis. Dosage modification is normally unnecessary in renal failure as the metabolites are less toxic than the parent compound. About 3% of the administered dose is excreted in the bile, but only 1% appears in the feces, and this mostly in inactive forms.
Interactions
Induction of liver microsomal enzymes, for example by phenobarbital (phenobarbitone) or rifampicin (rifampin), diminishes blood levels of chloramphenicol; conversely, chloramphenicol, which inhibits hepatic microsomal oxidases, potentiates the activity of dicoumarol (dicumarol), phenytoin, tolbutamide and those barbiturates that are eliminated by metabolism. It also depresses the action of cyclophosphamide, which depends for its cytotoxicity on transformation into active metabolites. It is uncertain whether this interaction may lead to a clinically significant level of inhibition of the activity of cyclophosphamide. The half-life of chloramphenicol is considerably prolonged if paracetamol (acetaminophen) is given concurrently, and co-administration of these drugs should be avoided.

Clinical Use

Typhoid fever and other severe infections due to salmonellae
Rickettsial infections
Meningitis
Invasive infection caused by H. influenzae
Destructive lung lesions involving anaerobes
Eye infections (topical)
Reference is made to its use in cholera, plague, tularemia and bartonellosis, melioidosis, Whipple’s disease and relapsing fever. In enteric fever in adults, fluoroquinolones are associated with a lower clinical relapse rate. Treatment for other serious infections should be restricted to organisms that are resistant or much less susceptible to other antibiotics. A study in low resource countries found ampicillin plus gentamicin superior to injectable chloramphenicol for the treatment of very severe communityacquired pneumonia in children.
It has been used with varying success to treat infections caused by glycopeptide-resistant enterococci. Meningitis caused by penicillin-resistant pneumococci responds poorly, apparently due to failure to achieve bactericidal concentrations in CSF. It should never be given systemically for minor infections. Topical use in the treatment of eye infections is controversial given the unsubstantiated risk of bone marrow aplasia. A placebo-controlled study in children with infective conjunctivitis in the community found no clinical benefit in the use of chloramphenicol eye drops.
The daily dose should not normally exceed 2 g, and the duration of the course should be limited (e.g. 10 days). Although patients may show toxic manifestations after receiving very little drug, the danger is almost certainly increased by excessive or repeated dosage or by the treatment of patients with impaired hepatic or renal function, including those at the extremes of life. The wide pharmacokinetic variability of the antibiotic in neonates makes monitoring of serum concentrations advisable. Determination of full blood counts should be carried out twice weekly.

Side Effects

Glossitis, associated with overgrowth of Candida albicans, is fairly common if the course of treatment exceeds 1 week. Stomatitis, nausea, vomiting and diarrhea may occur, but are uncommon. Hypersensitivity reactions are very uncommon. Jarisch–Herxheimer-like reactions have been described in patients treated for brucellosis, enteric fever and syphilis.
Bone marrow effects
Chloramphenicol exerts a dose-related but reversible depressant effect on the marrow of all those treated, resulting in vacuolization of erythroid and myeloid cells, reticulocytopenia and ferrokinetic changes indicative of decreased erythropoiesis. Evidence of bone-marrow depression is regularly seen if the plasma concentration exceeds 25 mg/L, and leukopenia and thrombocytopenia may be severe. There is no evidence that this common marrow depression is the precursor of potentially fatal aplasia, which differs in that it is fortunately rare, late in onset, usually irreversible and may follow the smallest dose. Aplasia can follow systemic, oral and even ophthalmic administration and may be potentiated by cimetidine. Liver disease, uremia and pre-existing bone marrow dysfunction may increase the risk. It is unusual for manifestations to appear during treatment, and the interval between cessation of treatment and onset of dyscrasia can be months. A few patients survive with protracted aplasia, and myeloblastic leukemia then often supervenes.
It is thought that the toxic agent is not chloramphenicol itself but an as yet unidentified metabolite. Chloramphenicol is partially metabolized to produce oxidized, reduced and conjugated products. The toxic metabolite may be a shortlived product of reduction of the nitro group, which damages DNA by helix destabilization and strand breakage.
Predisposition to aplasia may be explained by genetically determined differences in metabolism of the agent. Risk of fatal aplastic anemia has been estimated to increase 13-fold on average treatment with 4 g of chloramphenicol. Corresponding increases are 10-fold in patients treated with mepacrine (quinacrine) and 4-fold in patients treated with oxyphenbutazone.
Children
Infants given large doses may develop exceedingly high plasma levels of the drug because of their immature conjugation and excretion mechanisms. A life-threatening disorder called the ‘gray baby’ syndrome, characterized by vomiting, refusal to suck and abdominal distention followed by circulatory collapse, may appear when the plasma concentration exceeds 20 mg/L. If concentrations reach 200 mg/L, the disorder can develop in older children or even adults.
Optic neuritis has been described in children with cystic fibrosis receiving prolonged treatment for pulmonary infection. Most improve when the drug is discontinued, but central visual acuity can be permanently impaired. There is some experimental evidence that ear drops containing 5% chloramphenicol sodium succinate can damage hearing. One study identified an increased risk of acute leukemia following childhood administration of chloramphenicol, particularly for durations exceeding 10 days.

Safety Profile

Confirmed human carcinogen producing leukemia, aplastic anemia, and other bone marrow changes. Experimental tumorigenic data. Poison by intravenous and subcutaneous routes. Moderately toxic by ingestion and intraperitoneal routes. Human systemic effects by an unknown route: changes in plasma or blood volume, unspecified liver effects, and hemorrhaging. Experimental teratogenic and reproductive effects. Human mutation data reported. An antibiotic. When heated to decomposition it emits very toxic fumes of NOx and Cl-. See also other chloramphenicol entries.

Synthesis

Chloramphenicol, D-threo-2,2-dichloro-N-[|?-hydroxy-|á-(hydroxymethyl)]-n-nitrophenylacetamide (32.6.7), was first isolated in 1947 from a culture fluid of the actinomycete Streptomyces venezuelae; however, it is only currently produced synthetically. When using a synthetic racemic mixture without having previously separated it into D- and L-threo forms, it is called sintomycin. Two ways of synthesizing chloramphenicol are suggested. The first begins with 4-nitroacetophenone, which is brominated with molecular bromine to make |?-bromo-4-nitroacetophenone (32.6.1). This is transformed to |?-amino- 4-nitroacetophenone (32.6.2) by successive production of a quaternary salt with urotropine and subsequent break up to an amine using hydrogen chloride. The resulting aminoketone is acylated with acetic anhydride to make |?-acetamido-4-nitroacetophenone (32.6.3), and the product undergoes acylmethylation with paraform aldehyde to give |á-acetamido- |?-hydroxy-4-nitropropiophenone (32.6.4). Reducing the carbonyl group in the resulting compound with aluminum isopropoxide in isopropyl alcohol gives D,L-threo-2-acetamido- 1-(4-nitrophenyl)-1,3-propandiol (32.6.5). The acetyl group is hydrolyzed in hydrochloric acid to form D,L-threo-2-amino-1(4-nitrophenyl)-1,3-propandiol. The resulting racemic mixture of amines is treated with camphor-D-sulfonic acid, and the resulting enantiomeric salts are separated. After alkaline hydrolysis of the selected salt, the product D, (?)-threo-2- amino-1-(4-nitrophenyl)-1,3-propandiol (32.6.6) is synthesized. Acylating the aminogroup of this compound with the methyl ester of dichloroacetic acid gives the desired chloramphenicol (32.6.7).

The other synthesis begins with cinnamic alcohol, which is reacted with hypobromous acid to make 2-bromo-1-phenyl-1,3-propandiol (32.6.8), the hydroxyl group of which is protected as a ketal by reacting it with acetone, giving 5-bromo-2,2-dimethyl-4-phenyl- 1,3-dioxane (32.6.9). Reacting the resulting bromide with ammonia gives an isomeric mixture of D,L-threo-5-amino-2,2-dimethyl-4-phenyl-1,3-dioxane, which upon treatment with D-tartaric acid, separation of the resulting salts, and subsequent alkaline hydrolysis of the selected salt gives D-(?)-5-amino-2,2-dimethyl-4-phenyl-1,3-dioxane (32.6.10). Acylating this with the methyl ester of dichloroacetic acid gives D-(?)-threo-5-dichloroacetamido-2,2-dimethyl-4-phenyl-1,3-dioxane (32.6.11). The phenyl ring is then nitrated, during which the 1,3-dioxane ring is cleaved off, giving dinitrate of D-(?)-threo-2- dichloroacetamido-1-(4-nitrophenyl)-1,3-propandiol (32.6.12). Reducing the nitro group in this compound with bivalent iron sulfate gives the desired chloramphenicol (32.6.7).

Potential Exposure

An antibiotic derived from streptomyces venezuelae. A potential danger to those involved in the manufacture, formulation, and application of this antibiotic and antifungal agent

Veterinary Drugs and Treatments

Chloramphenicol is used for a variety of infections in small animals and horses, particularly those caused by anaerobic bacteria. The FDA has prohibited the use of chloramphenicol in animals used for food production because of the human public health implications.

Drug interactions

Potentially hazardous interactions with other drugs
Anticoagulants: effect of coumarins enhanced.
Antidiabetics: effect of sulphonylureas enhanced.
Antiepileptics: metabolism accelerated by phenobarbital and primidone (reduced concentration of chloramphenicol); increased concentration of fosphenytoin and phenytoin (risk of toxicity).
Antipsychotics: avoid with clozapine (increased risk of agranulocytosis).
Ciclosporin: possibly increases ciclosporin concentration.
Clopidogrel: possibly reduces antiplatelet effect.
Tacrolimus: possibly increases tacrolimus concentration.

First aid

If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids. Seek med?ical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Seek medical attention immediately. Ifthis chemical has been inhaled, remove from exposure,begin rescue breathing (using universal precautions, includ?ing resuscitation mask) if breathing has stopped and CPR if598 Chloramphenicolheart action has stopped. Transfer promptly to a medicalfacility. When this chemical has been swallowed, get medical attention. Give large quantities of water and inducevomiting. Do not make an unconscious person vomit.

Carcinogenicity

Chloramphenicol is reasonably anticipated to be a human carcinogen, based on limited evidence of carcinogenicity from studies in humans.

Environmental Fate

As an antibiotic, chloramphenicol enters the target cells by facilitated diffusion and binds reversibly to the 50S ribosomalsubunit. This prevents the interaction between peptidyl transferase and its amino acid substrate, which results in the inhibition of peptide bond formation. Indeed, it is an inhibitor of protein synthesis in the bacteria and to a lesser extent, in eukaryotic cells. Chloramphenicol can also inhibit mitochondrial protein synthesis in mammalian cells particularly erythropoietic cells, which are sensitive to the drug.

Metabolic pathway

Six metabolites of chloramphenicol are identified, among which the sulfate conjugate is characterized in goat urine.

Metabolism

Hepatic, with 90% conjugated to inactive glucuronide.

Metabolism

When given orally, it is rapidly and completely absorbed but has a fairly short half-life. It is mainly excreted in the urine in the form of its metabolites, which are a C-3 glucuronide, and, to a lesser extent, its deamidation product and the product of dehalogenation and reduction. These metabolites are all inactive. The aromatic nitro group also is reduced metabolically, and this product can undergo amide hydrolysis. The reduction of the nitro group, however, does not take place efficiently in humans but, rather, primarily occurs in the gut by the action of the normal flora. Chloramphenicol potentiates the activity of some other drugs by inducing liver metabolism. Such agents include anticoagulant coumarins, sulfonamides, oral hypoglycemics, and phenytoin.

storage

Color Code—Blue: Health Hazard/Poison: Storein a secure poison location. Prior to working withChloramphenicol you should be trained on its proper handling and storage. A regulated, marked area should beestablished where this chemical is handled, used, or storedin compliance with OSHA Standard 1910.1045. Store intightly closed containers in a cool, well-ventilated area.

Shipping

UN3249 Medicine, solid, toxic, n.o.s., Hazard Class: 6.1; Labels: 6.1-Poisonous materials. UN2811 Toxic solids, organic, n.o.s., Hazard Class: 6.1; Labels: 6.1- Poisonous materials, Technical Name Required.

Purification Methods

Purify chloramphenicol by recrystallisation from H2O (solubility is 2.5mg/mL at 25o) or ethylene dichloride as needles or long plates, and by sublimation at high vacuum. It has A 1cm 298 at max 278nm, and it is slightly soluble in H2O (0.25%) and propylene glycol (1.50%) at 25o but is freely soluble in MeOH, EtOH, BuOH, EtOAc and Me2CO. [Relstock et al. J Am Chem Soc 71 2458 1949, Confroulis et al. J Am Chem Soc 71 2463 1949, Long & Troutman J Am Chem Soc 71 2469, 2473 1949, Ehrhart et al. Chem Ber 90 2088 1957, Beilstein 13 IV 2742.]

Toxicity evaluation

In the aquatic system, chloramphenicol is not expected to adsorb to suspended solids and sediments given by the Koc (Soil Organic Carbon–Water Partitioning Coefficient) value of 99.
Chloramphenicol solutions are susceptible to direct photolysis by sunlight or high temperatures and decompose to form hydrochloric and dichloric acid. Hydrolysis of chloramphenicol is not anticipated under environmental conditions because it lacks a functional group to hydrolyze. Chloramphenicol has been reported to degrade 86.2% with a biodegradation rate of 3.3 mg COD per gram per hour using adapted activated sludge as the inoculums. It can also be degraded by intestinal bacteria via amidolysis to 18 observed metabolites.

Incompatibilities

Compounds of the carboxyl group react with all bases, both inorganic and organic (i.e., amines), releasing substantial heat, water, and a salt that may be harmful. Incompatible with arsenic compounds (releases hydrogen cyanide gas), diazo compounds, dithiocarbamates, isocyanates, mercaptans, nitrides, sulfides (releasing heat, toxic, and possibly flammable gases), thiosulfates, and dithionites (releasing hydrogen sulfate and oxides of sulfur).

Waste Disposal

It is inappropriate and possibly dangerous to the environment to dispose of expired or waste pharmaceuticals by flushing them down the toilet or discarding them to the trash. Household quantities of expired or waste pharmaceuticals may be mixed with wet cat litter or coffee grounds, double-bagged in plastic, discard in trash. Larger quantities shall carefully take into consideration applicable DEA, EPA, and FDA regulations. If possible return the pharmaceutical to the manufacturer for proper disposal being careful to properly label and securely package the material. Alternatively, the waste pharmaceutical shall be labeled, securely packaged, and transported by a state licensed medical waste contractor to dispose by burial in a licensed hazardous or toxic waste landfill or incinerator.