Chloramphenicol

Source: Wikipedia, the free encyclopedia.
Chloramphenicol
Clinical data
Trade namesChloromycetin, Abeed, others[1]
Other namesC/CHL/CL[2]
AHFS/Drugs.comMonograph
MedlinePlusa608008
License data
Pregnancy
category
  • AU: A
QJ51BA01 (WHO)
Legal status
Legal status
Pharmacokinetic data
Bioavailability75–90%
Protein binding60%
MetabolismLiver
Elimination half-life1.6–3.3 hours
ExcretionKidney (5–15%), faeces (4%)
Identifiers
  • 2,2-dichloro-N-[(1R,2R)-1,3-dihydroxy-1-(4-nitrophenyl)propan-2-yl]acetamide[4]
JSmol)
  • c1cc(ccc1[C@H]([C@@H](CO)NC(=O)C(Cl)Cl)O)[N+](=O)[O-]
  • InChI=1S/C11H12Cl2N2O5/c12-10(13)11(18)14-8(5-16)9(17)6-1-3-7(4-2-6)15(19)20/h1-4,8-10,16-17H,5H2,(H,14,18)/t8-,9-/m1/s1 checkY
  • Key:WIIZWVCIJKGZOK-RKDXNWHRSA-N checkY
  (verify)

Chloramphenicol is an

injection into a vein, it is used to treat meningitis, plague, cholera, and typhoid fever.[5] Its use by mouth or by injection is only recommended when safer antibiotics cannot be used.[5] Monitoring both blood levels of the medication and blood cell levels every two days is recommended during treatment.[5]

Common side effects include

stops bacterial growth by stopping the production of proteins.[5]

Chloramphenicol was discovered after being isolated from Streptomyces venezuelae in 1947.[8] Its chemical structure was identified and it was first synthesized in 1949. It is on the World Health Organization's List of Essential Medicines.[9] It is available as a generic medication.[5]

Medical uses

The original indication of chloramphenicol was in the treatment of

Salmonella typhi has meant it is seldom used for this indication except when the organism is known to be sensitive.[medical citation needed
]

In low-income countries, the WHO no longer recommends only chloramphenicol as first-line to treat meningitis, but recognises it may be used with caution if there are no available alternatives.[10]

During the last decade chloramphenicol has been re-evaluated as an old agent with potential against systemic infections due to multidrug-resistant gram positive microorganisms (including vancomycin resistant enterococci). In vitro data have shown an activity against the majority (> 80%) of vancomycin resistant E. faecium strains.[11]

In the context of preventing endophthalmitis, a complication of cataract surgery, a 2017 systematic review found moderate evidence that using chloramphenicol eye drops in addition to an antibiotic injection (cefuroxime or penicillin) will likely lower the risk of endophthalmitis, compared to eye drops or antibiotic injections alone.[12]

Spectrum

Chloramphenicol has a broad spectrum of activity and has been effective in treating ocular infections such as conjunctivitis, blepharitis etc. caused by a number of bacteria including Staphylococcus aureus, Streptococcus pneumoniae, and Escherichia coli. It is not effective against Pseudomonas aeruginosa. The following susceptibility data represent the minimum inhibitory concentration for a few medically significant organisms.[13]

  • Escherichia coli: 0.015 – 10,000 μg/mL
  • Staphylococcus aureus: 0.06 – 128 μg/mL
  • Streptococcus pneumoniae: 2 – 16 μg/mL

Each of these concentrations is dependent upon the bacterial strain being targeted. Some strains of

E coli, for example, show spontaneous emergence of chloramphenicol resistance.[14][15]

Resistance

Three mechanisms of

hydroxyl groups on the chloramphenicol molecule. The acetylation prevents chloramphenicol from binding to the ribosome. Resistance-conferring mutations of the 50S ribosomal subunit are rare.[medical citation needed
]

Chloramphenicol resistance may be carried on a plasmid that also codes for resistance to other drugs. One example is the

R factors).[medical citation needed
]

As of 2014 some Enterococcus faecium and Pseudomonas aeruginosa strains are resistant to chloramphenicol. Some Veillonella spp. and Staphylococcus capitis strains have also developed resistance to chloramphenicol to varying degrees.[16]

Adverse effects

Aplastic anemia

The most serious

blood counts of patients can prevent the development of aplastic anaemia, but patients are recommended to have a baseline blood count with a repeat blood count every few days while on treatment.[17] Chloramphenicol should be discontinued if the complete blood count drops. The highest risk is with oral chloramphenicol (affecting 1 in 24,000–40,000)[18] and the lowest risk occurs with eye drops (affecting less than one in 224,716 prescriptions).[19]

veterinary antibiotic, but is not approved for use in humans.[citation needed
]

Bone marrow suppression

Chloramphenicol may cause

mitochondria.[20] This effect manifests first as a fall in hemoglobin levels, which occurs quite predictably once a cumulative dose of 20 g has been given. The anaemia is fully reversible once the drug is stopped and does not predict future development of aplastic anaemia. Studies in mice have suggested existing marrow damage may compound any marrow damage resulting from the toxic effects of chloramphenicol.[21]

Leukemia

Leukemia, a cancer of the blood or bone marrow, is characterized by an abnormal increase of immature white blood cells. The risk of childhood leukemia is increased, as demonstrated in a Chinese case–control study,[22] and the risk increases with length of treatment.

Gray baby syndrome

Intravenous chloramphenicol use has been associated with the so-called gray baby syndrome.[23] This phenomenon occurs in newborn infants because they do not yet have fully functional liver enzymes (i.e. UDP-glucuronyl transferase), so chloramphenicol remains unmetabolized in the body.[24] This causes several adverse effects, including hypotension and cyanosis. The condition can be prevented by using the drug at the recommended doses, and monitoring blood levels.[25][26][27]

Hypersensitivity reactions

Fever, macular and vesicular rashes, angioedema, urticaria, and anaphylaxis may occur. Herxheimer's reactions have occurred during therapy for typhoid fever.[28]

Neurotoxic reactions

Headache, mild depression, mental confusion, and delirium have been described in patients receiving chloramphenicol. Optic and peripheral neuritis have been reported, usually following long-term therapy. If this occurs, the drug should be promptly withdrawn.[28]

Pharmacokinetics

Chloramphenicol is extremely lipid-soluble; it remains relatively unbound to protein and is a small molecule. It has a large apparent volume of distribution and penetrates effectively into all tissues of the body, including the brain. Distribution is not uniform, with highest concentrations found in the liver and kidney, with lowest in the brain and cerebrospinal fluid.[28] The concentration achieved in brain and cerebrospinal fluid is around 30 to 50% of the overall average body concentration, even when the meninges are not inflamed; this increases to as high as 89% when the meninges are inflamed.[citation needed]

Chloramphenicol increases the absorption of iron.[29]

Use in special populations

Chloramphenicol is metabolized by the liver to chloramphenicol glucuronate (which is inactive). In liver impairment, the dose of chloramphenicol must therefore be reduced. No standard dose reduction exists for chloramphenicol in liver impairment, and the dose should be adjusted according to measured plasma concentrations.

The majority of the chloramphenicol dose is excreted by the kidneys as the inactive metabolite, chloramphenicol glucuronate. Only a tiny fraction of the chloramphenicol is excreted by the kidneys unchanged. Plasma levels should be monitored in patients with renal impairment, but this is not mandatory. Chloramphenicol succinate ester (an intravenous prodrug form) is readily excreted unchanged by the kidneys, more so than chloramphenicol base, and this is the major reason why levels of chloramphenicol in the blood are much lower when given intravenously than orally.[30] Chloramphenicol passes into breast milk, so should therefore be avoided during breast feeding, if possible.[31]

Dose monitoring

Plasma levels of chloramphenicol must be monitored in neonates and patients with abnormal liver function. Plasma levels should be monitored in all children under the age of four, the elderly, and patients with kidney failure. Because efficacy and toxicity of chloramphenicol are associated with a maximum serum concentration, peak levels (one hour after the intravenous dose is given) should be 10–20 µg/ml with toxicity > 40 µg/ml; trough levels (taken immediately before a dose) should be 5–10 µg/ml.[32][33]

Drug interactions

Administration of chloramphenicol concomitantly with bone marrow depressant drugs is contraindicated, although concerns over aplastic anaemia associated with ocular chloramphenicol have largely been discounted.[34]

Chloramphenicol is a potent inhibitor of the

antifungals, tricyclic antidepressants, macrolide antibiotics, SSRIs, statins, cardiac antiarrhythmics, antivirals, anticoagulants, and PDE5 inhibitors.[28][36]

Drug antagonistic

Chloramphenicol is antagonistic with most cephalosporins and using both together should be avoided in the treatment of infections.[37]

Drug synergism

Chloramphenicol has been demonstrated a synergistic effect when combined with fosfomycin against clinical isolates of Enterococcus faecium.[38]

Mechanism of action

Chloramphenicol is a

protein chain elongation by inhibiting the peptidyl transferase activity of the bacterial ribosome. It specifically binds to A2451 and A2452 residues[39] in the 23S rRNA of the 50S ribosomal subunit, preventing peptide bond formation.[40] Chloramphenicol directly interferes with substrate binding in the ribosome, as compared to macrolides, which sterically block the progression of the growing peptide.[41][42][43]

History

Chloramphenicol was first isolated from Streptomyces venezuelae in 1947 and in 1949 a team of scientists at Parke-Davis including Mildred Rebstock published their identification of the chemical structure and their synthesis.[8]: 26 [44][45]

In 1972, Senator Ted Kennedy combined the two examples of the Tuskegee Syphilis Study and the 1958 Los Angeles Infant Chloramphenicol experiments as initial subjects of a Senate Subcommittee investigation into dangerous medical experimentation on human subjects.[46]

In 2007, the accumulation of reports associating aplastic anemia and blood dyscrasia with chloramphenicol eye drops led to the classification of “probable human carcinogen” according to World Health Organization criteria, based on the known published case reports and the spontaneous reports submitted to the National Registry of Drug-Induced Ocular Side Effects.[47]

Society and culture

Names

Chloramphenicol is available as a generic worldwide under many brandnames[48] and also under various generic names in eastern Europe and Russia, including chlornitromycin, levomycetin, and chloromycetin; the racemate is known as synthomycetin.[49]

Formulations

Pure chloramphenicol

Chloramphenicol is available as a capsule or as a liquid. In some countries, it is sold as chloramphenicol

palmitate ester (CPE). CPE is inactive, and is hydrolysed to active chloramphenicol in the small intestine. No difference in bioavailability is noted between chloramphenicol and CPE.[citation needed
]

Manufacture of oral chloramphenicol in the U.S. stopped in 1991, because the vast majority of chloramphenicol-associated cases of aplastic anaemia are associated with the oral preparation. No oral formulation of chloramphenicol is available in the U.S. for human use.[50]

In molecular biology, chloramphenicol is prepared in ethanol.[citation needed]

Intravenous

The

intravenous (IV) preparation of chloramphenicol is the succinate ester. This creates a problem: Chloramphenicol succinate ester is an inactive prodrug and must first be hydrolysed to chloramphenicol; however, the hydrolysis process is often incomplete, and 30% of the dose is lost and removed in the urine. Serum concentrations of IV chloramphenicol are only 70% of those achieved when chloramphenicol is given orally.[51] For this reason, the dose needs to be increased to 75 mg/kg/day when administered IV to achieve levels equivalent to the oral dose.[52]

Oily

Oily chloramphenicol (or chloramphenicol oil suspension) is a long-acting preparation of chloramphenicol first introduced by Roussel in 1954; marketed as Tifomycine, it was originally used as a treatment for

typhoid. Roussel stopped production of oily chloramphenicol in 1995; the International Dispensary Association Foundation has manufactured it since 1998, first in Malta and then in India from December 2004.[53]

Oily chloramphenicol was first used to treat meningitis in 1975[54] and numerous studies since have demonstrated its efficacy.[55][56][57] It is the cheapest treatment available for meningitis (US$5 per treatment course, compared to US$30 for ampicillin and US$15 for five days of ceftriaxone). It has the great advantage of requiring only a single injection, whereas ceftriaxone is traditionally given daily for five days. This recommendation may yet change, now that a single dose of ceftriaxone (cost US$3) has been shown to be equivalent to one dose of oily chloramphenicol.[58]

Eye drops

Chloramphenicol is used in topical preparations (

aplastic anaemia following use of chloramphenicol eyedrops exist, but the risk is estimated to be of the order of less than one in 224,716 prescriptions.[19] In Mexico, this is the treatment used prophylactically in newborns for neonatal conjunctivitis.[59]

Veterinary uses

Although its use in veterinary medicine is highly restricted, chloramphenicol still has some important veterinary uses.[60] It is currently considered the most useful treatment of chlamydial disease in koalas.[61][62] The pharmacokinetics of chloramphenicol have been investigated in koalas.[63]

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