Chloramphenicol and Macrolides

1. Antibiotics inhibiting protein synthesis:
Chloremphenicol and Macrolides
Dr Ravi Kant Agrawal, MVSc, PhD
Senior Scientist (Veterinary Microbiology)
Food Microbiology Laboratory
Division of Livestock Products Technology
ICAR-Indian Veterinary Research Institute
Izatnagar 243122 (UP) India

2. Amphenicols
• Chloramphenicol
• Thiamphenicol (with SH-group instead of N02-group):
less ADRs but less antibacterial activity
• Florfenicol (analog of thiamphenicol)
Chlorephenicol:
• Contains nitrobenzene Moiety
• Derivative of dichloroacetic acid Chlormycetin
• It is a non-ionized, highly lipophilic compound that
enters bacterial cells by passive diffusion

3. Chloramphenicol
• Originally isolated from Streptomyces venezuale.
• Chloramphenicol was the first broad-spectrum
antibacterial developed (1947).
• It is now produced synthetically because has a very
simple structure.
• Although an effective broad-spectrum antibiotics;
limited clinical use because of serious toxicity.
• Mainly bacteriostatic
• Due to resistance and safety concerns, it is no longer a
first-line agent for any infection in developed nations,
with the notable exception of topical treatment of
bacterial conjunctivitis.

4. Mechanism of Action of Chloroamphenicol
• Attaches at P sites of 50 S subunit of microbial
ribosomes and inhibits functional attachment of amino-
acyl end of AA-t-RNA to 50S subunit (A site).
• Failure to properly align prevents Peptidyl transferase
enzyme from transferring the growing chain from the "P"
site to the bound charged tRNA in the "A" site. This
stops protein synthesis.
• Chloramphenicol does inhibit mitochondrial ribosomal
protein synthesis because these ribosomes are 70S, the
same as those in bacteria. It does not bind to the 80S
mammalian ribosomes. This may be responsible for the
dose related anemia caused by chloramphenicol.

6. Pharmacological activity
• Well absorbed after oral administration
• Distribution is Wide and Rapid, Distributed into total
body water
• Crosses BBB, can reach 60% (45-90%) of plasma
concentration in presence or absence of meningitis
• Excellent penetration into CSF, ocular and joint fluids
• Highest concentration found in Liver and kidney
• Chloramphenicol succinate used for parenteral
administration is highly water soluble
• Metabolized by liver – glucuronidation
• 68-99% excreted via urine
• T1/2: 1.5 to 4 hrs
• Rapidly excreted in urine, 10% as chloramphenicol; 90%
as glucuronide conjugate
• Systemic dosage need not be altered in renal
insufficiency but must be reduced markedly in hepatic
failure
• Newborns less than a week old and premature infants
also clear Chloramphenicol less well, dosage should be
reduced at 25 mg/kg/d

7. ANTIMICROBIAL ACTIVITY
• Broad spectrum antibiotic.
• Chloramphenicol is primarily bacteriostatic, but it may
be bactericidal to some strains of microorganisms even
at lower concentration: H. influenzae, N. meningitidis N.
gonorrhoeae and Bacteroides fragilis
• Bacteriostatic for – S. epidermidis, S. aureus, , M.
pneumonia, L. monocytogenes, Corynebacterium
diphtheriae, L. multocida, Salmonella sp., Shigella sp.,
E. coli, Rickettsia and Anaerobes
• Ineffective for Chlamydial infections
• More effective than Tetracyclines against Typhoid Fever
and other Salmonella infections.

8. Clinical uses
• Few uses as systemic drug because of toxicity.
• Because of potential toxicity, bacterial resistance, and the
availability of many other effective alternatives, chloramphenicol is
rarely used.
• It may be considered for treatment of serious rickettsial infections
such as typhus and Rocky Mountain spotted fever.
• It is an alternative to a beta-lactams for treatment of meningococcal
meningitis occurring in patients who have major hypersensitivity
reactions to penicillin or bacteria meningitis caused by penicillin-
resistant strains of pneumococci.
• Used as backup drug for severe infections caused by Salmonella
Typhi and Paratyphi
• Infections caused by anaerobes like B. fragilis
• Commonly used as topical agent
• Occasionally used topically in the treatment of eye
infections for its well penetration to ocular tissues
and the aqeous humor
• Used only in serious infections with the sensitive bacteria.

9. Resistance
• Selection of permeability mutants that results in impaired
penetration of the drug to target site.
• Production of chloramphenicol acetyltransferase/
chloramphenicol transacetylase, a plasmid-encoded
enzyme that inactivates the drug.

10. Adverse effects
• Adults occasionally develop Gastrointestinal reaction: nausea,
vomiting, and diarrhea. This is rare in children.
• Superinfections such as Oropharyngeal candidiasis, vaginal
candidiasis and acute Staphylococcal enterocolitis may occur
as a result of alteration of normal microbial flora.
• Chloramphenicol causes a dose-related reversible suppression
of red cell production at dosages exceeding 50 mg/kg/d after 1–
2 weeks.
• Aplastic anaemia, a rare consequence (1 in 24 000 to 40 000
courses of therapy) of chloramphenicol administration by any
route. It tends to be irreversible and can be fatal.
• Chloramphenicol inhibits protein synthesis in the mitochondria
(70s ribosomes) of human cells. This inhibition may be the
cause of the dose dependent toxicity of drug to bone marrow.
• Premature infants: Gray baby syndrome
• Tolerated in older infants
• Decreased RBC, cyanosis and cardiovascular collapse
• Hypersensitivity reactions
• A rare anemia, probably immunological in origin but often fatal.

11. Adverse effects: gray baby syndromegray baby syndrome
• Newborn infants lack an effective glucuronic acid conjugation
mechanism for the degradation and detoxification of
chloramphenicol (Mainly due to deficiency of hepatic glucoronyl
transferase ).
• Consequently, when infants are given dosages above 50 mg/kg/d,
the drug may accumulate, resulting in the gray baby syndromegray baby syndrome,
with vomiting, flaccidity, hypothermia, gray color, shock, and
collapse.
• Cyanosis, respiratory irregularities, abdominal distention, loose
green stool, and an ashen-gray color characterize this often-fatal
syndrome.
• To avoid this toxic effect, chloramphenicol should be used with
caution in infants and the dosage limited to 50 mg/kg/d or less
(during the first week of life) in full-term infants.
• The inadequate renal elimination mechanism of neonate and the
inactive metabolites also contributes to the occurrence of the
syndrome.
• Chloramphenicol inhibits hepatic microsomal enzymes that
metabolize phenytoin,Tolbutamide,Chlorpropamide, Anticoagulants
and warfarin.

12. Gray baby syndromeGray baby syndrome

13. Disadvantage:
bone marrow
toxicity
Advantage:
good penetration
including
in brain and eyes

14. Gram-positive
bacteria
Streptococcus pyogenes,
Viridans group streptococci.
Some Streptococcus
pneumoniae
Gram-negative
bacteria
Haemophilus influenzae,
Neisseria spp. Salmonella
spp. Shigella spp.
Anaerobic
bacteria
Bacteroides fragilis. Some
Clostridia spp. Other
anaerobic Gram-positive
and Gram negative bacteria
Atypical
bacteria
Rickettsia spp. Chlamydia
trachomatis, Mycoplasma
spp.
The Antimicrobial Activity of Chloramphenicol

15.  Florfenicol is a structural analog of thiamphenicol.
 It has greater in vitro activity against pathogenic
bacteria than chloramphenicol and thiamphenicol.
 It is also active against enteric bacteria, resistant to
chloramphenicol.
 It can cause dose-related bone marrow suppression but
has not been reported to cause fatal aplastic anemia in
humans.
 Currently, it is approved for use only in cattle,
aquaculture and pigs.
 In cattle florfenicol is used to treat infectious
conjunctivitis and respiratory disease caused by
bacteria like PasteurellaPasteurella andand Haemophilus.Haemophilus.
Florfenicol

16. ForfeniciolForfeniciol (Norfenicol(Norfenicol®®
))

17. Macrolides and Ketolides
 Erythromycin was derived from
Streptomyces erythreus.
 The basic structure is a lactone ring
 14-membered lactone ring-
Erthromycin, Clarithromycin,
Roxithromycin, Telithromyin
(ketolide).
 15-membered lactone ring-
Azithromycin
 16-membered lactone ring-
Spiramycin, Josamycin
 The structures of erythromycin and
telithromycin - Circled substituents
distinguish telithromycin from the
macrolides.
 Substituent allows telithromycin to
bind to a second site on the
bacterial ribosome.
 Old Generation: Erythromycin,
Oleandomycin, Troleandomycin,
Spiramycin, Josamycin
 New Generation: Rosaramycin,
Roxithromycin, Clarithromycin,
Azithromycin, Dirithromycin

18. Mechanism of Action of Macrolide Antibiotics
• Macrolides bind tightly
to the P site of 50S
subunit of the bacterial
ribosome, thus
blocking the Aminoacyl
translocation (exit of
the newly synthesized
peptide and formation
of initiation complex.
• Thus, they are
interfering with
bacterial translation.

19. RESISTANCE
Resistance to erythromycin is usually plasmid encoded.
Three mechanisms have been identified:
(1) Reduced permeability of the cell membrane or active
efflux
(2) Production (by Enterobacteriaceae) of esterases that
hydrolyze macrolides
(3) Modification of the ribosomal binding site (so-called
ribosomal protection) by chromosomal mutation or by
a macrolide-inducible or constitutive methylase.
Cross-resistance is complete between erythromycin and
the other macrolides.

20. Uses of Macrolide Antibiotics
• Active against a broad range of bacteria
• Effective against some staphylococci and streptococci,
but not usually used for MRSA or penicillin-resistant
streptococci
• Most aerobic Gram- bacteria are resistant
• Active against campylobacter, mycoplasma, legionella,
• Active against many atypical bacteria and some
mycobacteria and spirochetes.
Azithromycin
• Conc. in tissues and phagocytes higher than plasma.
• Slow release allows once a week dosing (half life 2-4
days).
• Especially useful for chlamydial infections
Clarithromycin
– Used for Mycobacterium avium

21. - Prototype macrolide
- Distributed into total body water
- Poor CSF penetration
- Food interferes with absorption.
- Serum half life is approx. 1.5 h normally and 5 hours in
patients with anuria
- Not removed by dialysis
- Metabolized in the liver
- Traverses the placenta and reaches the fetus
Spectrum:
- Erythromycin has a narrow Gram (+) spectrum similar to
Penicillin G.
- Also active against Chlamydia and Legionella organisms
Erythromycin

22. Commercial Preparations:
- Oral- stearate, ethyl succinate, estolate salts – 250-500
mg q 6 h adults
40 mg/kg/d - children
- Parenteral- lactobionate, gluceptate – 0.5-1 g q 6 hours
for adults
20-40 mg/kg/d for children
Erythromycin
● Erythromycin is the drug of choice for treatment of
Campylobacter jejuni infections.
● It is one of the drugs of choice for treatment of
Mycoplasma infections.
● Erythromycin has greater activity against
Staphylococcus than lincomycin but not clindamycin.

23. Adverse Effects
• GIT dysfunction: Anorexia, nausea, vomiting, and
diarrhea accompany oral administration.
• GI intolerance, which is due to a direct stimulation of
gut motility, is the most common: reason for
discontinuing erythromycin and substituting another
antibiotic.
• Erythromycin can produce acute cholestatic
hepatitis/jaundice (fever, jaundice, impaired liver
function), probably as a hypersensitivity reaction.
• Most patients recover from this, but hepatitis recurs if
the drug is re-administered.
• Erythromycin metabolites can inhibit cytochrome P450
enzymes and thus increase the serum concentrations of
theophylline, oral anticoagulants, cyclosporine,
methylprednisolone, and digoxin.

24. - Clarithromycin is derived from erythromycin by
addition of a methyl group and has improved acid
stability and oral absorption compared with
erythromycin.
-Clarithromycin and erythromycin are
virtually identical with respect to antibacterial activity
except that clarithromycin is more active against
M. avium complex.
-Clarithromycin also has activity
against M. leprae, T. gondii, and H. pylori.
-Erythromycin-resistant streptococci and
staphylococci are also resistant to clarithromycin.
-The advantages of clarithromycin compared with
erythromycin are lower incidence of GI
intolerance and less frequent dosing.
-More active against Gram (+) pathogens, Legionella
and Chlamydia than Erythromycin
-Lower frequency of GIT effects
-Less frequent dosing
-Half life of 6 hours
- Given at 250-500 mg twice daily
Clarithromycin

25. - More active than erythromycin against several Gram (-) pathogens
- Maintains high concentrations for prolonged periods into a number
of tissues (lungs, tonsil, cervix)
- Tissue half life – 2 - 4 days
- Long half-life allows once daily oral administration and shortening
of treatment in many cases ( a single 1 g dose of azithromycin is as
effective as a 7 day course of doxycycline for chlamydial cervicitis
and urethritis).
- Community acquired pneumonia – 500 mg loading dose, followed
by a 250 mg Single daily dose for the next 4 days
- Should be administered 1 hour before or 2 hours after meals;
- Aluminum and magnesium delay absorption and reduce peak serum
concentrations
- Does not inactivate cytochrome p450 enzymes and free of the drug
interactions that occur with erythromycin and clarithromycin
Azithromycin

26. • Azithromycin has spectrum of
activity and clinical uses
virtually identical to those of
clarithromycin.
• Azithromycin is active against
M. avium complex and T. gondii.
• Azithromycin is slightly less
active than erythromycin and
clarithromycin against
staphylococci and streptococci
and slightly more active against
H. influenzae.
• Azithromycin is highly active
against chlamydia.
• Azitrhromycin penetrates into
phagocytes so that it is effective
against intracellular tubercle
bacilli.

27. AZITHROMYCIN

28. Gram-positive
bacteria
Some Streptococcus pyogenes.
Some viridans streptococci, Some
Streptococcus pneumoniae. Some
Staphylococcus aureus.
Gram-negative
bacteria
Neiseria spp. Some Haemophilus
influenzae. Bordetella pertussis
Anaerobic
bacteria
Atypical
bacteria
Chlamydia spp. Mycoplasma spp.
Legionella pneumophila, Some
Rickettsia spp.
Mycobacteria Mycobacterium avium complex,
Mycobacterium leprae.
Spirochetes Treponema pallidum, Borrelia
burgdorferi.
The macrolide group consists of Erythromycin, Clarithromycin, and
Azithromycin (all oral, with erythromycin and azithromycin also being
available parenterally).

29. ● Spiramycin is less active against bacteria than
erythromycin in vitro but more active in vivo because of
exceptional ability to concentrate in tissues.
● It excretes mainly with saliva and is marketed in
combination with metronidazole, for treatment of oral
infections in dogs and cats.
• Rodogyl® (spiramycin/metronidazole)
Spiramycin

30.  Fidaxomicin (Dificid®
) is a
macrolide in a adults ≥18 years of
age for treatment of Cl. difficile-
associated diarrhrea.
 It is a tablet taken orally two
times a day for 10 days, with or
without food.
 Fidaxomicin inhibitits C.
difficile sporulation and of
clostridial toxin production.

31. KETOLIDES
• Semisynthetic 14 membered ring macrolides
• Telithromycin
• Active in vitro against S pyogenes, S. penumoniae, S.
aureus, H. influenzae, Moraxella catarrhalis,
mycopasmas, Legionella sp, Chlamydia sp,
Helicobacter pylori, N. gonorrhoaea, B. fragilis, T.
gondii and non-tuberculosis mycobacteria.

32. - Oral bioavailability – 57%
- Good tissue and intracellular penetration
- Metabolized in the liver
- Eliminated by a combination of biliary and urinary
routes
of excretion
- Administered as a once daily dose of 800 mg
- Indicated for treatment of respiratory tract infections,
including community acquired bacterial pneumonia,
acute exacerbations of chronic bronchitis, sinusitis and
streptococcal pharyngitis
- A reversible inhibitor of the CYP3A4 enzyme system
Pharmacokinetics

33. TELITHROMYCIN

34. Uses of Telithromycin (a ketolide)
• Telithromycin is approved for use against bacterial
respiratory infections
• Active against most strains of Streptococcus
pneumoniae, including penicillin- and macrolide-
resistant strains
• Also active against more strains of Staphylococci
• Only available in oral formulation

35. Gram-positive
bacteria
Streptococcus pyogenes,
Streptococcus pneumoniae,
Some Staphylococcus
aureus
Gram-negative
bacteria
Some Haemophilus
influenzae, Bordetella
pertussis
Anaerobic
bacteria
Atypical
bacteria
Chlamydia spp. Mycoplasma
spp. Legionella
pneumophila
The related ketolide class consists of Telithromycin (oral)

36. Thanks
Acknowledgement: All the material/presentations available
online on the subject are duly acknowledged.
Disclaimer: The author bear no responsibility with regard to the
source and authenticity of the content.