Comparative and Veterinary Pharmacology

Table 2Mechanisms of drug resistance(modified from CLSI M31-A3)
Class Examples Mechanisms of resistance
Aminocyclitols Apramycin Modifying enzymes
Efflux
Ribosomal mutations

Spectinomycin

Aminoglycosides Gentamicin Modifying enzymes
Decreased permeability
Target site modification/mutation
Efflux

Kanamycin
Neomycin
Streptomycin
b-lactam/b-lactamase inhibitor
combinations

Amoxicillin/clavulanic

acid

Inactivating enzymes –b-lactamases

Cephalosporins
(first-generation)

Cefadroxil Inactivating enzymes –b-lactamases

Reduced permeability

Altered pencillin-binding proteins

Efflux

Cefazolin
Cephalexin
Cephapirin
Cephalosporins
(second-generation)

Cefaclor
Cefuroxime
Cephalosporins
(third-generation)

Cefotaxime
Cefpodoxime
Ceftiofur
Cephalosporins
(fourth-generation)

Cefepime
Cefquinome
Carbapenems Imipenem
Meropenem
Folate Pathway Inhibitors Sulfonamides Decreased permeability
Production of drug-insensitive
enzymes
Overexpression of sensitive enzymes

Trimethoprim
Trimethoprim-
sulfamethoxazole
Glycopeptides Vancomycin Target site (cell wall) resistance
Teicoplanin
Lincosamides Clindamycin Decreased ribosomal binding
Lincomycin Inactivating enzymes
Pirlimycin
Macrolides
(14-membered ring)

Erythromycin Target site (ribosome) modification/

mutation

Decreased permeability

Inactivating enzymes

Efflux

Macrolides
(15-membered ring)

Azithromycin
Gamithromycin
Tulathromycin
Macrolides
(16-membered ring)

Aivlosin
Spiramycin
Tilmicosin
Tylosin
Class Examples Mechanisms of resistance
Orthosomycins Avilamycin Decreased ribosomal binding
Oxazolidinones Linezolid Ribosomal mutations
Ribosomal modification
Penicillins Amoxicillin Inactivating enzymes –b-lactamases
Reduced permeability
Altered pencillin-binding proteins
Efflux

Ampicillin

Penicillin

Oxacillin

(continued)

234 M. Martinez and P. Silley