7. β-Lactams
• β-lactam antimicrobial agents all share the common, central, four-
member β-lactam ring
• Inhibition of cell wall synthesis as the primary mode of action.
• Additional ring structures or substituent groups added to the β-
lactam ring determine whether the agent is classified as a penicillin,
cephem, carbapenem, or monobactam.
8. Penicillin
• Penicillins are primarily active against non-β-lactamase–producing, aerobic,
gram-positive, some fastidious, aerobic, gram-negative, and some
anaerobic bacteria.
• Aminopenicillins (ampicillin and amoxicillin) are active against additional
gram-negative species, including some members of the
Enterobacteriaceae.
• Carboxypenicillins (carbenicillin and ticarcillin) and ureidopenicillins
(mezlocillin and piperacillin) are active against a considerably expanded list
of gram-negative bacteria, including many Pseudomonas and Burkholderia
spp.
• Penicillinase-stable penicillins (cloxacillin, dicloxacillin, methicillin, nafcillin,
and oxacillin) are active against predominantly gram-positive bacteria,
including penicillinase-producing staphylococci
9. β-Lactam/β-Lactamase Inhibitor
Combinations (BLBLIs)
• Clavulanic acid, sulbactam, and tazobactam, avibactam, vaborbactam,
relebactam.
• The results of tests of only the β-lactam portion of the combination
against β-lactamase–producing organisms are often not predictive of
susceptibility to the two-drug combination.
10. Cephems (Including Cephalosporins)
• Exhibit somewhat different spectrums of activity against aerobic and
anaerobic, gram-positive and gram-negative bacteria
• Cephalosporins are often referred to as “first-,” “second-,” “third-,” or
“fourth generation” cephalosporins, based on the extent of their
activity against the more antimicrobial agent– resistant, gram-
negative aerobic bacteria
• No effect on anaerobes and enterococci
11. Carbapenems
• Carbapenems and penems
• Differs slightly in structure from the penicillin class
• A penem is a type of β-lactam with an unsaturated five-member
heterocycle containing a sulfur atom fused to the β-lactam ring.
• Penems do not occur naturally; all are synthetic.
• Related to penems are carbapenems, which have a carbon atom in
place of the sulfur atom
• Agents in this class are much more resistant to β-lactamase
hydrolysis, which provides them with broad-spectrum activity against
many gram-positive and gram-negative bacteria
12. Monobactams
• Monobactam antimicrobial agents are monocyclic β-lactams
• Has activity only against aerobic, gram-negative bacteria
• Aztreonam- only monobactam antimicrobial agent approved for use
in the United States by the FDA
14. Aminoglycosides
• Aminoglycosides are structurally related antimicrobial agents that
inhibit bacterial protein synthesis at the ribosomal level
• This class includes agents variously affected by aminoglycoside-
inactivating enzymes
• Aminoglycosides are used primarily to treat aerobic, gram-negative
rod infections or in synergistic combinations with cell wall– active
antimicrobial agents (eg, penicillin, ampicillin, vancomycin) against
some resistant, gram-positive bacteria, such as enterococci
15. Folate Pathway Inhibitors
• Sulfamethoxazole is usually tested in combination with trimethoprim,
because these two antimicrobial agents inhibit sequential steps in the
folate pathway of some gram-positive and gram-negative bacteria
16. Glycopeptides
• Glycopeptide antimicrobial agents
• which include vancomycin and teicoplanin
• share a complex chemical structure and a principal mode of action of
inhibition of cell wall synthesis at a different site than that of the β-lactams
• The activity of this group is directed primarily at
aerobic, gram-positive bacteria
• Vancomycin is an accepted agent for treatment of
• Gram-positive bacterial infection eg, MRSA and some enterococci)
• in the penicillin-allergic patient
17. Lipopeptides
• Lipopeptides are antimicrobial agents- the principal target is the cell membrane
• The polymyxin subclass
• Has activity against gram-negative organisms.
• polymyxin B and colistin
• Daptomycin is a cyclic lipopeptide
• Has activity against gram-positive organisms
• Lipopeptide activity is strongly influenced by the presence of divalent cations
• The presence of excess calcium cations inhibits the activity of the polymyxins,
• Whereas the presence of physiological levels (50 mg/L) of calcium ions is essential for the
proper activity of daptomycin
18. Macrolides
• Macrolides are structurally related antimicrobial agents that inhibit
bacterial protein synthesis at the ribosomal level
• against fastidious, gram-negative bacterial isolates and gram-positive
organisms
• The macrolide group of antimicrobial agents consists of several
subgroups
• azithromycin, clarithromycin, dirithromycin, the ketolide telithromycin, and
the fluoroketolide solithromycin.
19. Nitroimidazoles
• Nitroimidazoles- metronidazole and tinidazole are bactericidal agents
that are converted intracellularly in susceptible organisms to
metabolites that disrupt the host deoxyribonucleic acid (DNA)
• active only against strictly anaerobic bacteria
20. Oxazolidinones
• The oxazolidinone class is a class of antimicrobial agents with a
unique mechanism of action that inhibits protein synthesis
• The first agent approved in this class was linezolid which has activity
against only gram positive organisms
21. Quinolones
• Quinolones (quinolones and fluoroquinolones) are structurally related
antimicrobial agents that function primarily by inhibiting the DNA-
gyrase or topoisomerase activity of many gram-positive and gram-
negative bacteria
• Some differences in spectrum may require separate testing of the
individual agents.
• N acid, ciprofloxacin, levoflox, moxi and few more
22. Streptogramins
• Streptogramins, which include quinupristin-dalfopristin and
linopristin-flopristin, are combinations of two cyclic peptides
produced by Streptomyces spp.
• They work synergistically to inhibit protein synthesis, mainly in gram-
positive organisms, although they do have limited activity against
some gram-negative and anaerobic organisms.
23. Tetracyclines
• Tetracyclines are structurally related antimicrobial agents that inhibit
protein synthesis at the ribosomal level of certain gram-positive and
gram-negative bacteria.
• Organisms that are susceptible to tetracycline are also considered
susceptible to doxycycline and minocycline
• Tigecycline, a glycylcycline, is a derivative of minocycline that has
activity against organisms that may be resistant to other tetracyclines
24. Single-Drug Classes
The following antimicrobial agents (antimicrobial classes) are currently the only members of their respective
classes used in humans
• Chloramphenicol (phenicols) inhibit protein synthesis
• Clindamycin (lincosamides) inhibit protein synthesis
• fusidic acid (steroidal) inhibit protein synthesis
• mupirocin (pseudomonic acid) inhibit protein synthesis
• spectinomycin (aminocyclitols) inhibit protein synthesis;
• rifampin (ansamycins)
• Rifamycin (rifaximin) inhibits protein synthesis: poor absorption when given orally; hepatic ncephalopathy
• fidaxomicin (macrocyclics), which are ribonucleic acid (RNA) synthesis inhibitors
• Nitrofurantoin (nitrofurans), which is used only in the therapy of urinary tract infections, acts by inhibiting
several protein synthesis-and-assembly steps at the ribosomal level
• Fosfomycin (fosfomycins), approved by the FDA for urinary tract infections only, inhibits enzymes involved in
cell wall synthesis
