Classes of antimicrobial agents

Antibiotics, antifungals, antihelminths, antivirals

1. MBSM 713: BIOCHEMISTRY OF ANTI
MICROBIAL AGENTS
Lecture Two:
Survey of major antimicrobial
drug groups
1.ANTIBACTERIAL AGENTS
(Antibiotics)
Dr. G. Kattam Maiyoh
01/23/15 1
GKM/KISIIU/MBSM713 /BIOC.AMIC.AGENS.LEC02

2. Classification: Mode of action
01/23/15 2
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

3. Inhibitors of Cell Wall Synthesis
01/23/15 3
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

4. 01/23/15 4
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02
Bacterial cell wall
•There are three types
–Gram-positive (e.g. Staphylococci,
Listeria
•Have many peptidoglycan
layers
•stains with crystal violet
•typically lack the outer
membrane found in gram-ve.
–Gram-negative (e.g. E.coli,
Salmonella)
•Have few peptidoglycan layers
•(stain safranin or fuchsin)
–Acid-fast Positive (Mycobacteria)
•Cell wall contains waxy
substance (Mycollic acid)
•Stains with acid fast (heating
required)

5. Antibiotics - Cell wall synthesis inhibitors
Beta-lactam antibiotics:
1928 - Alexander Fleming
observes the
antibacterial effects of
Penicillin
1940 - Florey and Chain
extract Penicillin
01/23/15 5
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

6. The beta lactams
•The β-lactam group of antibiotics
includes an enormous diversity of
natural and semi-synthetic
compounds that inhibit several
enzymes associated with the final
step of peptidoglycan synthesis.
•All of this enormous family are
derived from a β -lactam structure: a
four-membered ring in which the β
-lactam bond resembles a peptide
bond.
•The multitude of chemical
modifications based on this four-
membered ring permits the
astonishing array of antibacterial and
pharmacological properties within
this valuable family of antibiotics.
01/23/15 6
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

7. The Beta-Lactams
01/23/15
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02
7
R – variable side chain
Monobactam nucleus

8. Penicillinase (b Lactamase)
- Represents a great challenge to the action of the beta lactams
Figure 20.8
More when we discuss antibiotic resistance
01/23/15 8
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

9. •Penicillium notatum produces the
only naturally occurring agent –
penicillin G or benzylpenicillin
•Penicillium chrysogenum produces
6-aminopenicillanic acid, raw
material for semi-synthetics
penicillins
01/23/15 9
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

10. Targets for beta lactams
1. The targets for β-lactam drugs are the penicillin binding
proteins (PBP's), so called because they bind radioactive
penicillin and can be detected by autoradiography of gels on
which bacterial proteins have been separated
electrophoretically.
•The penicillin binding proteins have transpeptidase or
carboxypeptidase activity and they act to regulate cell size and
shape.
•They are also involved in septum formation and cell division. Bacteria have
several individual penicillin binding proteins, each with a separate function.
•Conventionally these are numbered according to size, with PBP 1 as the
largest protein.
•The PBP 1 of one bacterium will not necessarily have the same function as
the PBP 1 of a different organism.
01/23/15 10
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

11. Target
2. The β-lactam antibiotics also stimulate the activity of
autolysins by inactivating an inhibitor => lysis
•Autolysins are enzymes that are responsible for the natural
turnover of cell wall polymers to permit growth of the cells.
•Under normal conditions, these enzymes produce
controlled weak points within the peptidoglycan
structure to allow for expansion of the cell wall structure.
•This activity is stimulated by β-lactams, causing a
breakdown of peptidoglycan and leading to osmotic
fragility of the cell and ultimately to cell lysis.
01/23/15 11
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

12. Penicillins - classification
– Narrow spectrum – penicillinase sensitive
– Narrow spectrum – penicillinase resistant
– Broad spectrum penicillins
– Extended-spectrum penicillins
• Cephalosporines
• Carbapenems
• Monobactams
• Vancomycin, Bacitracin
01/23/15 12
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

13. Penicllins (pharmacokinetics)
•Attains therapeutic concentration in
most tissues
•However has poor CSF penetration
•Renal excretion (Excretion)
•Side effects: hypersensitivity, nephritis,
neruotoxicity, platelet dysfunction
01/23/15 14
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

14. Narrow spectrum – penicillinase (= β-lactamase)
sensitive
• Benzylpenicillin
– Naturally occuring
– Poor oral availability (sensitive to stomach acid)
=> given by injection
– Active against gram-positive bacteria
• Phenoxymethylpenicillin
– Better oral availability (acid resistant)
01/23/15 15
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

15. Narrow spectrum – penicillinase (= β-lactamase) resistant
• Methicillin
– Semisynthetic
– Poor oral availability (only parenteral)
– Active against gram-pos bacteria
– Mostly used for Staphylococcus aureus
• Oxacillin
– Good oral availability
• Cloxacillin
• Dicloxacillin
01/23/15 16
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

16. Broad spectrum – penicillinase (β-
lactamase) sensitive
(Also referred to as Aminopenicillins)
• Ampicillin
– Semisynthetic
– Good oral availability
– Active against gram-pos and gram-neg bacteria
– Active against enterobacteria e.g. kleb. Shig. Salm
• Amoxicillin
– Excellent oral availability
01/23/15 17
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

17. Extended spectrum – penicillinase (β-
lactamase) sensitive
(Also called Carboxypenicillins)
• Carbenicillin
– Semisynthetic
– Poor oral availability
– Active against gram-pos and gram-neg bacteria
– Active against Pseudomonas aeruginosa and
Klebsiella
• Ticarcillin
• Mezlocillin
• Pipercillin
01/23/15 18
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

18. Penicillins
Figure 20.6
01/23/15 19
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

19. 01/23/15
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02
20

20. Cephalosporins
•Share the same antibiotic mechanism as penicillins
•Cross-allergies with penicillins are common
•Some CSs antagonize Vitamin K => leads to bleeding
•Some CSs block alcohol oxidation => disulfiram effect (allergic
reactions, seizures, extreme tiredness and dark urine)
Classified into generations: 1- 4
• Increasing activity against gram-negative bacteria and
anaerobes
• Increasing resistance to destruction by beta-lactamases
• Increasing ability to reach cerebrospinal fluid
01/23/15 21
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

21. Cephalosporins
•The first to be discoverded were called first
generation while later, more extended spectrum
cephalosporins were classified as second, third and
4th generation cephalosporins in this order.
•Each newer generation has significantly greater gram-
negative antimicrobial properties than the preceding
generation,
• Most cases with decreased activity against gram-
positive organisms.
•Fourth generation cephalosporins, however, have true
broad spectrum activity.
01/23/15 22
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

22. 01/23/15 23
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

23. 01/23/15
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02
24
Cephalosporin structure

24. •Base molecule is 7-
aminocephalosporanic acid
produced by a Sardinian
sewer mold
•R groups determine
spectrum of activity and
pharmacological properties
•Mechanism of
action/resistance and class
pharmacology is essentially
the same as penicillins
01/23/15 25
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

25. First Generation Cephalosporins
•Cefazolin, cephalexin,
cephadroxil
•Excellent against susceptible
staph and strep
•Modest activity against G -ve
•Cefazolin given parentally,
others orally
•More than half of the drug is
bound to plasma proteins
•Excreted by kidneys
unmetabolized
•Good for staph and strep skin
and soft tissue infections
01/23/15 26
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

26. Second Generation Cephalosporins
•Include;
–Cefaclor,
– cefuroxime,
–cefprozil
•Modest activity against G+, increased activity
against G-, works against anaerobes
•Cefaclor and cefprozil given orally
•Absorption and excretion same as first
generation.
•Good for treating respiratory tract infections,
intra-abdominal infections, pelvic
inflammatory disease, diabetic foot ulcers
01/23/15 27
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

27. Third Generation Cephalosporins
•Ceftaxime, ceftriaxzone,
cefoperazone, cefpodoxime
•Broad spectrum killers
•Drugs of choice for serious
infections
•No effect against Listeria and beta-
lactamase producing pneumococci
•Cefpodoxime given orally, others
parentally
•Most excreted by kidney
•Therapeutic uses
–Bacterial meningitis
–Lyme disease
–Life-threatening G -ve sepsis
(infection)
01/23/15 28
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

28. Fourth Generation Cephalosporin
– e.g.Cefepime
–Have true broad spectrum activity ( and
more beta-lactamases resistanc (effective
against Gm+ and Gm-)
–Given parentally, excellent penetration into
CSF
–Good for nosocomial infections
01/23/15 29
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

29. 01/23/15
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02
30

30. Toxicity/Contraindications
of Cephalosporins
•Hypersensitivity reactions (uncommon) essentially
same as for penicillins
•Cross-reaction between 2 classes
01/23/15 31
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

31. Inhibitors of Cell Wall Synthesis
01/23/15 33GKM/KISIIU/MBSM713 /BIOC.AMIC.AGENS.LEC02

32. Carbapenems
•Beta-lactam ring is
fused to a 5 member
ring system
•Effect on microbes
and pharmacology
of carbapenems
similar to penicillins
01/23/15 34GKM/KISIIU/MBSM713 /BIOC.AMIC.AGENS.LEC02

33. Selected Carbapenems
•Imipenem
–Broad spectrum including anaerobes
and Pseudomonas aeruginosa
–Parentally administered
–Must be combined with cilastatin to be
absorbed
–Excreted by kidneys
•Meropenem, ertapenem, and doripenem
are similar to imipenem but don’t need co-
administration with cilastatin
cilastatin chemical compound which inhibits the human enzyme dehydropeptidase
01/23/15 35GKM/KISIIU/MBSM713 /BIOC.AMIC.AGENS.LEC02

34. Toxicity/Contraindications
of Carbapenems
•Nausea and vomiting (common)
•Hypersensitivity reactions (uncommon)
–Essentially the same as for penicillins
–Cross-reactivity is possible
01/23/15 36
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

35. Aztrenam – a monobactam
•Monobactam - beta-lactam compounds
wherein the beta-lactam ring is alone and not
fused to another ring
•Works only on Gm -ve, including Pseudomonas
aeruginosa
•Useful for treating G-ve infections that require
a beta-lactam because it does not elicit
hypersensitivity reactions
01/23/15 37GKM/KISIIU/MBSM713 /BIOC.AMIC.AGENS.LEC02

36. Beta-lactamase inhibitors
a. Clavulanic acid
– Irreversible inhibitor of β-lactamase
– Good oral absorption
– Combined with amoxicillin or ticarcillin
b. Sulbactam
01/23/15 38GKM/KISIIU/MBSM713 /BIOC.AMIC.AGENS.LEC02

37. Peptide Antibiotics
Peptide antibiotics are drugs with
polypeptides structure
Sub-group of Peptide Antibiotics
Polymyxins e.g.
»Polymyxin B
»Colistin
Glycopeptides e.g.
»Vancomycin
»Teicoplanin
»Avoparcin
Bacitracin
Streptogramins
Each drug group has its own mechanism of
action
4 groups and 4 mechanism
01/23/15 39
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

38. PolymyxinsPolymyxins
Drug members
Polymyxin B
Colistin (Polymyxin E)
Mechanism of action
Detergent-like action
Damage to cell membrane function
Bind to Lipopolysaccharides (LPS) and
destroy outer membrane of Gram-
negative bacteria
Bactericidal
Concentration-dependent
Non-selective on bacterial membrane
Spectrum of activity
Gram-negative bacteria
01/23/15 40
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

39. PolymyxinsPolymyxins
•Pharmacokinetics
–Not absorbed via GI tract
–If injection, drug accumulated and
slowly excreted
•Toxicities
–Highly toxic if systemic injection
–Nephrotoxic
–Neurotoxic
•Clinical uses
–Oral treatment
–Local treatment
01/23/15 41
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

40. GlycopeptidesGlycopeptides
•Group members
–Vancomycin
•Antibacterial activity
–Inhibition of cell wall synthesis
–Active against Gram-positive bacteria
•Not absorbed orally, must
administered IV
•High toxicity
–Local irritation , ototoxicity,
nephrotoxicity
•Clinical uses
–Hardly used in animals
–Used only resistant case i.e. to beta-
lactams
01/23/15 42
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

41. BacitracinBacitracin
•Drug activity
–Inhibit cell wall synthesis
–Activity on Gram-positive bacteria
–Bactericidal
•Nephrotoxic if systemic injection
•Clinical uses – the same as polymyxin
–Oral – as growth promoter
–Local or topical drugs
01/23/15 43
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

42. Antibiotics that Inhibit Protein Synthesis
01/23/15 44
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

43. Protein synthesis inhibitors
– Aminoglycosides
– Tetracyclins
- Spectinomycin
– Macrolides
– Chloramphenicol
– Clindamycin
01/23/15
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02
45

44. Inhibition of Protein Synthesis by Antibiotics
Figure 20.4
01/23/15 46
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

45. Review of Initiation of Protein Synthesis
30S
13
2GTP
123GTP
Initiation Factors
mRNA
3
1
2GTP
30S
Initiation
Complex
f-met-tRNA
Spectinomycin
Aminoglycosides
1
2
GDP + Pi
50S
70S
Initiation
Complex
AP
01/23/15 47
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

46. Review of Elongation of Protein Synthesis
GTP
AP
TuGTP TuGDP
Ts
Ts
Tu
+
GDP
Ts
Pi
PA
Tetracycline
AP
Erythromycin
Fusidic Acid
Chloramphenicol
GGTP
GGDP+Pi
G
GDP
AP
+
GTP
01/23/15 48
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

47. Antimicrobials that Bind to the 30S
Ribosomal Subunit
01/23/15 49
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

48. a) Aminoglycosides (bactericidal)
streptomycin, kanamycin, gentamicin, tobramycin, amikacin,
netilmicin, neomycin (topical)
•Mode of action - The aminoglycosides irreversibly bind
to the 16S ribosomal RNA and freeze the 30S initiation
complex (30S-mRNA-tRNA) so that no further initiation
can occur.
•They also slow down protein synthesis that has already
initiated and induce misreading of the mRNA.
–By binding to the 16 S r-RNA the aminoglycosides increase
the affinity of the A site for t-RNA regardless of the anticodon
specificity.
•May also destabilize bacterial membranes.
01/23/15 50
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

49. Microbe Library
American Society for Microbiology
www.microbelibrary.org
01/23/15 51
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

50. b) Aminoglycosides (bactericidal)
streptomycin, kanamycin, gentamicin, tobramycin, amikacin,
netilmicin, neomycin (topical)
•Spectrum of Activity –Effective against many gram-
negative and some gram-positive bacteria;
•Not useful for anaerobic (oxygen required for uptake of
antibiotic) or intracellular bacteria.
•Resistance - Common
•Synergy - The aminoglycosides synergize with β -lactam
antibiotics. The β -lactams inhibit cell wall synthesis and
thereby increase the permeability of the aminoglycosides.
01/23/15 52GKM/KISIIU/MBSM713 /BIOC.AMIC.AGENS.LEC02

51. c) Tetracyclines (bacteriostatic)
tetracycline, minocycline and doxycycline
•Mode of action - The tetracyclines reversibly bind to the 30S
ribosome and inhibit binding of aminoacyl-t-RNA to the acceptor site
on the 70S ribosome.
•Spectrum of activity - Broad spectrum; Useful against intracellular
bacteria
•Resistance - Common
•Adverse effects - Destruction of normal intestinal flora resulting in
increased secondary infections; staining and impairment of the
structure of bone and teeth.
01/23/15 53
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

52. d) Spectinomycin (bacteriostatic)
•Mode of action - Spectinomycin reversibly interferes with m-RNA
interaction with the 30S ribosome. It is structurally similar to the
aminoglycosides but does not cause misreading of mRNA.
•Spectrum of activity - Used in the treatment of penicillin-resistant
Neisseria gonorrhoeae
•Resistance - Rare in Neisseria gonorrhoeae
01/23/15 54
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

53. Antimicrobials that Bind to the 50S
Ribosomal Subunit
01/23/15 55
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

54. a) Chloramphenicol, Lincomycin,
Clindamycin (bacteriostatic)
•Mode of action - These antimicrobials bind to the 50S ribosome and
inhibit peptidyl transferase activity.
•Spectrum of activity - Chloramphenicol - Broad range;
Lincomycin and clindamycin - Restricted range
•Resistance - Common
•Adverse effects - Chloramphenicol is toxic (bone marrow suppression) but
is used in the treatment of bacterial meningitis.
01/23/15 56
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

55. b) Macrolides (bacteriostatic)
erythromycin, clarithromycin, azithromycin, spiramycin
•Mode of action - The macrolides inhibit translocation.
•Spectrum of activity - Gram-positive bacteria,
Mycoplasma, Legionella
•Resistance - Common
01/23/15 57
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

56. Macrolides : ClassificationMacrolides : Classification
•Macrolides are drugs with lactone ring
structure
•Sub-groups are based on no. of ring atom
–12-membered ring macrolides
–13-membered
–14-membered (many drugs)
–15-membered
–16-membered (many drugs)
•Special groups
–Azalides – name for 15-membered
–Triamilides – name for tulathromycin
(combination of 13- and 15-membered)
–Ketolides – name for 14-membered with 3
keto group
01/23/15 58
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

57. MacrolidesMacrolides
Drug examples
13-membered
Tulathromycin (Triamilides)
14-membered
Erythromycin
Clarithromycin, Roxithromycin,
Dirithromycin
15-membered
Azithromycin (Azalides)
Tulathromycin (Triamilides)
16-membered
Spiramycin
Tylosin
01/23/15 59
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

58. Macrolides – general Macrolides – general
propertiesproperties
•Mechanism of
action
–Inhibit protein
synthesis
–Bind to 50S
ribosomal unit
–Bacteriostatic
•Spectrum of
activity
–Gram-positive
–Some Gram-
negative
–Anaerobes
–Mycoplasma
01/23/15 60
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

59. Macrolides Macrolides
Pharmacokinetics
Broad distribution in body
tissues
High intracellular
concentration
01/23/15 61
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

60. MacrolidesMacrolides
Additional properties
of Macrolides
•Anti-inflammatory
effect
–Inhibitory effect on
neutrophils
–inhibit
proinflammatory
cytokines
–Useful for treatment
of inflammatory
pulmonary disease
•Prokinetic effect
–Stimulate movement
of GI tract
01/23/15 62
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

61. ErythromycinErythromycin
•Erythromycin is a standard or basic drug of
macrolides
•Other drug members are usually compared
with erythromycin
•Important adverse effect - severe diarrhea
–Especially in adult horse and ruminants
•Clinical uses
–Second choice (alternative drug) in
humans
–Small animals
–Fowls
–Some cases in ruminants
01/23/15 63
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

62. Tylosin andTylosin and SpiramycinSpiramycin
•Tylosin and Spiramycin
–Activities are similar
to erythromycin
–Good activity on
Mycoplasma
•Examples of Clinical
uses
–Whooping couph
–Pneumonia
–VDs
–Used in ruminants
and pigs
01/23/15 64
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

63. Advanced generation Advanced generation
MacrolidesMacrolides
Example drugs
Roxithromycin
Dirithromycin
Clarithromycin
Azithromycin
General activity – the same as erythromycin
Better Pharmacokinetic properties
Acid stable
Fewer GI side effect
Higher oral availability
Longer serum half-lives
Higher tissue concentrations
01/23/15 65
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

64. KetolidesKetolides
•Ketolides are 14-
membered ring
macrolides with 3
keto group
•Specific drugs
–Telithromycin
–Cethromycin (still
in clinical study)
•Important
properties
–Less resistance
–Good activities on
bacteria resistant
to erythromycin
01/23/15 66
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

65. Fusidic acid (bacteriostatic)
•Selectivity due to differences in prokaryotic and
eukaryotic elongation factors
•Mode of action - Fusidic acid binds to elongation
factor G (EF-G) and inhibits release of EF-G from the
EF-G/GDP complex.
•Spectrum of activity - Gram-positive cocci
01/23/15 67GKM/KISIIU/MBSM713 /BIOC.AMIC.AGENS.LEC02
Antimicrobials that Interfere with
Elongation Factors

66. Inhibitors of Nucleic Acid Synthesis
~Inhibitors of DNA synthesis
~Inhibitors of RNA synthesis
01/23/15 69
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

67. Inhibitors of RNA Synthesis
For this class of antibiotics, selectivity is due to
differences between prokaryotic and eukaryotic RNA
polymerase i.e.
All RNA polymerases are multi-protein complexes,
however, the number of proteins that are assembled
to form the active enzyme is much larger in eukaryotes;
•The basic catalytic core is made up of 12 subunits.
•By comparison, bacterial RNAP has 5 subunits.
01/23/15 70
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

68. Rifampin, Rifamycin, Rifampicin, Rifabutin
(bactericidal)
•Mode of action - These antimicrobials bind to DNA-dependent RNA
polymerase and inhibit initiation of mRNA synthesis.
•Spectrum of activity - Broad spectrum but is used most commonly
in the treatment of tuberculosis
•Resistance – Common
–For example;
–Resistance to rifampicin develops quickly during treatment, so
monotherapy should not be used to treat these infections — it
should be used in combination with other antibiotics.
–Resistance to rifampicin arises from mutations that alter
residues of the rifampicin binding site on RNA polymerase,
resulting in decreased affinity for rifampicin.
•Combination therapy - Since resistance is common, rifampin is
usually used in combination therapy.
01/23/15 71
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

69. Inhibitors of DNA Synthesis
For this class of antibiotics, selectivity due to differences between prokaryotic
and eukaryotic DNA replication enzymes
Consider the following:
Eukaryotic replication is more complicated.
•First, they have multiple ori per chromosome that allow for
bidirectional synthesis of the linear chromosome.
•They also use several DNA polymerases (I, II, III), and ligase (seals the
nicks in the DNA strand), and RNA primer (gives a 3' end for the DNA
polymerase to start synthesis).

•As for other differences in their synthesis of DNA is their speed,
prokaryotes can replicate their chromosome at about 1,000 bp/sec, while
eukaryotes can replicate their chromosomes at about 100 bp/sec.
•They also differ in the number of ori, eukaryotes (as it was stated above)
has multiple ori, while prokaryotes have only one.
01/23/15 72
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

70. The Quinolones
•Current drugs are
fluoridated 4-quinolones
•Broad coverage (some
broader than others)
•Targets DNA gyrase ( G-)
and topoisomerase IV
(G+)
•Resistance due to efflux
and mutations in targets
01/23/15 73
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

71. Pharmacological attributes of Quinolones
•Favorable pharmacological attributes
–Orally administered, quickly absorbed,
even with a full stomach
–Excellent bioavailability in a wide
range of tissues and body fluids
(including inside cells)
•Mostly cleared by the kidneys
–Exceptions are pefloxacin and
moxifloxacin which are metabolized by
liver
•Ciprofloxacin, ofloxacin, and pefloxacin
are excreted in breast milk
““Got Cipro?”Got Cipro?”
01/23/15 74
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

72. Therapeutic Uses
of Quinolones
•Urinary tract
infections
•Prostatitis
•STD’s
–Chlamydia
–Chancroid - painful
sores on the genitalia
–Not syphilis or
gonorrhea (due to
increased resistance)
01/23/15 75
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

73. Therapeutic Uses of Quinolones
•GI and abdominal
–Travelers diarrhea
–Shigellosis
–Typhoid fever
•Respiratory tract
–New agents for strep. pneumonia
01/23/15 76
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

74. Therapeutic Uses
of Quinolones
•Bone, joint, soft tissue
–Ideal for chronic
osteomylitis - infection of
the bone or bone marrow
•Resistance developing in
S. aureus, P. aeruginosa,
and S. marcesens
–Good against
polymicrobial infections
like diabetic foot ulcers
01/23/15 77
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

75. Therapeutic Uses
of Quinolones
•Ciprofloxacin for anthrax
and tuleremia (rabbit fever, deer
fly fever, Ohara's fever)
•Combined with other drugs,
useful for atypical
Mycobacterium sp.
Pulmonary AnthraxPulmonary Anthrax
01/23/15 78
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

76. Toxicity/Contraindications of Quinolones
•Nausea, vomiting, abdominal discomfort (common)
•Diarrhea and antibiotic-associated colitis (uncommon to rare)
•CNS side effects
–Mild headache and dizziness (common to rare)
–Hallucinations, delirium, and seizures (rare)
•Arthropy in immature animals (common)
–Quinolones not given to children unless benefits outweigh the risks
•Leukopenia, eosinophilia, heart arythmias (rare)
delirium - disorder involving incoherent speech, hallucinations, etc., caused by
intoxication, fever, etc
01/23/15 79
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

77. Antimetabolite Antibiotics
01/23/15 80
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

78. Inhibitors of Folic Acid Synthesis
•Basis of Selectivity
•Review of Folic
Acid Metabolism
p-aminobenzoic acid + Pteridine
Dihydropteroic acid
Dihydrofolic acid
Tetrahydrofolic acid
Pteridine
synthetase
Dihydrofolate
synthetase
Dihydrofolate
reductase
Thymidine
Purines
Methionine
Trimethoprim
Sulfonamides
01/23/15 81
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

79. Sulfonamides, Sulfones (bacteriostatic)
•Mode of action - These antimicrobials are analogues of para-
aminobenzoic acid and competitively inhibit formation of
dihydropteroic acid.
•Spectrum of activity - Broad range activity against gram-
positive and gram-negative bacteria; used primarily in urinary
tract and Nocardia infections.
•Resistance - Common
•Combination therapy - The sulfonamides are used in
combination with trimethoprim; this combination blocks two
distinct steps in folic acid metabolism and prevents the
emergence of resistant strains.
01/23/15 82
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

80. Trimethoprim, Methotrexate,
Pyrimethamine (bacteriostatic)
•Mode of action - These antimicrobials binds to dihydrofolate
reductase and inhibit formation of tetrahydrofolic acid.
•Spectrum of activity - Broad range activity against gram-
positive and gram-negative bacteria; used primarily in urinary
tract and Nocardia infections.
•Resistance - Common
•Combination therapy - These antimicrobials are used in
combination with the sulfonamides; this combination blocks
two distinct steps in folic acid metabolism and prevents the
emergence of resistant strains.
01/23/15 83
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

81. Sulfonamides
•Analogues of para-aminobenzoic
acid
•Broad spectrum
•Competitive inhibitors of
dihydropteroate synthase – needed
for folic acid synthesis
Gerhard Domagk gets a Nobel Gerhard Domagk gets a Nobel
for Medicine, 1939.for Medicine, 1939.
01/23/15 84
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

82. Sulfonamides
•Mostly absorbed from GI tract
•Binds variably to serum albumin
•Wide tissue distribution, including
transplacentally
•Variably inactivated in liver by
acetylation and then excreted in
urine
•Some agents can precipitate in acid
urine
01/23/15 85
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

83. 1. Rapidly Absorbed and Eliminated
Sulfonamides
•Sulfisoxazole,
sulfamethoxazole, sulfadiazine
•Bind extensively to plasma
proteins
•Highly concentrated in urine
(cidal)
•Sulfamethoxazole combined
with trimethoprim (Bactrim) is
widely used to treat a variety
of infections (esp. UTI)
01/23/15 86
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

84. 2. Poorly Absorbed Sulfonamides
•E.g. Sulfasalazine
•Poorly absorbed in GI tract
•Used to treat ulcerative colitis
and irritable bowel syndrome
•Gut flora metabolize drug into
2 compounds, 1 toxic-
sulfapyridine, 1 therapeutic
(5-aminosalicylate)
•Hence is a prodrug – effective
after breakdown
Ulcerative Colitis
01/23/15 87
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

85. Sulfonamides for Topical Use
•E.g. 1.Sulfacetamide
–Good penetration in eye
–Non-irritating
•2. Silver sulfadiazine
–Prevention and treatment of
burn wound infections
Bacterial corneal infectionBacterial corneal infection
01/23/15 88
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

86. Long Acting Sulfonamide
•Serum half-life is
measured in days rather
than minutes or hours
•E.g. Sulfadoxine
•Combined with
pyirethamine to treat
malaria
Plasmodium vivaxPlasmodium vivax
01/23/15 89
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

87. Therapeutic Uses of Sulfonamides
•Urinary tract infections
•Nocardiosis -serious infection
caused by a fungus-like bacterium
that begins in the lungs and can
spread to the brain.
•Toxoplasmosis - caused
by protozoan (avoid using in
pregnant women)
Nocardia asteroidesNocardia asteroides
01/23/15 90
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

88. Toxicity/Contraindications
of Sulfonamides - UT
•Crystallization in acid
urine
–Common to uncommon
depending on drug.
–Alkalize urine or increase
hydration
01/23/15 91
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

89. Toxicity/Contraindications
of Sulfonamides - blood
•Acute hemolytic anemia
–Rare to extremely rare
–Associated with glucose-6-phosphate
dehydrogenase activity in RBC
•Agranulocytosis - failure of the bone marrow to make enough white
blood cells (neutrophils). (extremely rare)
•Aplastic anemia - marrow doesn't make enough new blood cells.
(extremely rare)
01/23/15 92
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

90. Toxicity/Contraindications
of Sulfonamides - immune
•Hypersensitivity reactions
(common to uncommon)
–Skin and mucous membrane
manifestations (rashes)
–Serum sickness - type III hypersensitivity
reaction that results from the injection of
heterologous or foreign protein or serum
–Focal or diffuse necrosis of the liver
(rare)
01/23/15 93
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

91. Toxic Epidermal Necrolysis (TEN)
01/23/15 94
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

92. Toxicity/Contraindications
of Sulfonamides - miscellaneous
•Nausea, anorexia, vomiting
(common)
•Kernicterus; damage caused by
excessive jaundice
–Displacement of bilirubin from
plasma albumin to brain
resulting in
encephalopathy(disease of
the brain)
–Never give sulfa drugs to a
pregnant or lactating woman
•Potentiation of oral coagulants,
sulfonylurea hypoglycemic drugs,
and hydrantoin anticonvulsants
Bilirubin deposits in neonatal Bilirubin deposits in neonatal
brainbrain
01/23/15 95
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02

93. INJURY TO THE PLASMA MEMBRANE - Brief
•All cells are bound by a cell membrane.
•And although the membranes of all cells are quite
similar, those of bacteria and fungi differ from
eukaryotic cells.
•These slight differences allow for selective action of
some antimicrobial agents.
•Certain antibiotics, like polymyxins, act as detergents
to dissolve bacterial cell membranes by binding to
phospholipids present in the membranes.
01/23/15
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02
96

94. The End
Thank you for Listening
01/23/15
GKM/KISIIU/MBSM713
/BIOC.AMIC.AGENS.LEC02
97