Updated: 12/30/2021

Antibiotic Classification & Mechanism

Topic

Review Topic

N/A

Questions

Evidence

Videos / Pods

Topic

Overview of By Mechanism

PENICILLINS	CEPHALOSPORINS	FLUOROQUINOLONES	AMINOGLYCOSIDES	MONOBACTAMS	CARBAPENEMS	MACROLIDES	OTHER
Natural	First generation	Ciprofloxacin (Cipro) Levofloxacin (Levaguin) Moxifloxacin (Avelox) Norfloxacin	Amikacin Gentamicin Kanamycin Neomycin Tobramycin	Aztreonam	Ertapenem Imienem Meropenem	Azithromycin Clarithromycin Dirithromycin Erythromycin Clindamycin	Vancomycin Rifampin Doxycycline Linezolid Tetracycline Trimethoprim/ sulfamethoxacole
Penicillin G Penicillin-VK	Cephalothin Cefazolin (Ancef, Kefzol) Cephapririn Cephalexin (Keflex) other
Penicillinase Resistant	Second Generation
Methicillin Nafcillin Oxacillin other	Cefacor Cefotetan (Cefotan) other
Aminopenicillins	Third Generation
Ampicillin	Ceftriaxone (Rocephin) other
	Fourth Generation
	Cefpirome Cefepime

Antibiotic Grouping By Mechanism
Cell Wall Synthesis	Penicillins Cephalosporins Vancomycin Beta-lactamase Inhibitors Carbapenems Aztreonam Polymycin Bacitracin
Protein Synthesis Inhibitors	Inhibit 30s Subunit Aminoglycosides (gentamicin) Tetracyclines Inhibit 50s Subunit Macrolides Chloramphenicol Clindamycin Linezolid Streptogramins
DNA Synthesis Inhibitors	Fluoroquinolones Metronidazole
RNA synthesis Inhibitors	Rifampin
Mycolic Acid synthesis inhibitors	Isoniazid
Folic Acid synthesis inhibitors	Sulfonamides Trimethoprim

Antibiotic Classification & Indications

Inhibits Cell Wall Synthesis
Penicillins (bactericidal: blocks cross linking via competitive inhibition of the transpeptidase enzyme)
Class/Mechanism	Drugs	Indications (Drug of Choice)	Toxicity
Penicillin	Penicillin G Aqueous penicillin G Procaine penicillin G Benzathine penicillin G Penicillin V	Strep. pyogenes (Grp.A) Step. agalactiae (Grp.B) C. perfringens(Bacilli)**	Hypersensitivity reaction Hemolytic anemia
Aminopenicillins	Ampicillin Amoxicillin	Above + ↑ Gram-negative: E. faecalis** E. Coli**	Above
Penicillinase-resistant-penicillins	Methicillin Nafcillin Oxacillin Cloxacillin Dicloxacillin	Above + PCNase-producingStaph. aureus	Above + Interstitial nephritis
Antipseudomonal penicillins	Carbenicillin Ticarcillin Piperacillin	Above + Pseudomonas aeruginosa**	Above
Cephalosporins (bactericidal: inhibits bacterial cell wall synthesis via competitive inhibition of the transpeptidase enzyme)
1st generation	Cefazolin Cephalexin	Staph. aureus Staph. epidermidis Some Gram-negatives: E. Coli Klebsiella	Allergic reaction Coombs-positive anemia (3%)
2nd generation	Cefoxitin Cefaclor Cefuroxime	Above + ↑ Gram-negative	Allergic Reaction ETOH Disulfiram reaction
3rd generation	Ceftriaxone Cefotaxime Ceftazidime Cefepime (4th generation)	Above + ↑ Gram-negative Pseudomonas	Allergic Reaction ETOH Disulfiram reaction
Other Cell Wall Inhibitors
Vancomycin (bactericidal: disrupts peptioglycan cross-linkage)	Vancomycin	MRSA PCN/Ceph allegies S. aureus S. epidermidis	Red man syndrome Nephrotoxicity Ototoxicity
Beta-lactamase Inhibitors (bactericidal: blocking cross linking)	Clavulanic Acid Sulbactam Tazobactam	S aureus S epidermis E.Coli Klebsiella	Hypersensitivity Reaction Hemolytic anemia
Carbapenems	Imipenem (+ cilastatin) Meropenem Doripenem Ertapenem	Broadest activity of any antibiotic (except MRSA, Mycoplasma)
Aztreonam	Aztreonam	Gram-negative rods Aerobes Hospital-acquired infections
Polymyxins	Polymyxin B Polymyxin E	Topical Gram-negative infections
Bacitracin	Bacitracin	Topical Gram-positive infections
Protein Synthesis Inhibition
Anti-30S ribosomal subunit
Aminoglycosides (bactericidal: irreversible binding to 30S)	Gentamicin Neomycin Amikacin Tobramycin Streptomycin	Aerobic Gram-negatives Enterobacteriaceae Pseudomonas	Nephrotoxicity Ototoxicity
Tetracyclines (bacteriostatic: blocks tRNA)	Tetracycline Doxycycline Minocycline Demeclocycline	Rickettsia Mycoplasma Spirochetes (Lyme's disease)	Hepatotoxicity Tooth discoloration Impaired growth Avoid in children < 12 years of age
Anti-50S ribosomal subunit
Macrolides (bacteriostatic: reversibly binds 50S)	Erythromycin Azithromycin Clarithromycin	Streptococcus H. influenzae Mycoplamsa pneumonia	Coumadin Interaction (cytochrome P450)
Chloramphenicol (bacteriostatic)	Chloramphenicol	H influenzae Bacterial Meningitis Brain absces	Aplastic Anemia Gray Baby Syndrome
Lincosamide (bacteriostatic: inhibits peptidyl transferase by interfering with amino acyl-tRNA complex)	Clindamycin	Bacteroides fragilis S aureus Coagulase-negative Staph & Strep Excellent Bone Penetration	Pseudomembranous colitis Hypersensitivity Reaction
Linezolid (variable)	Linezolid	Resistant Gram-positives
Streptogramins	Quinupristin Dalfopristin	VRE GAS and S. aureus skin infections
DNA Synthesis Inhibitors
Fluoroquinolones (bactericidal: inhibit DNA gyrase enzyme, inhibiting DNA synthesis)
1st generation	Nalidixic acid	Steptococcus Mycoplasma Aerobic Gram +	Phototoxicity Achilles tendon rupture Impaired fracture healing
2nd generation	Ciprofloxacin Norfloxacin Enoxacin Ofloxacin Levofloxacin	As Above +Pseudomonas	as above
3rd generation	Gatifloxacin	As above + Gram-positives	as above
4th generation	Moxifloxacin Gemifloxacin	As above + Gram-positives + anaerobes	as above
Other DNA Inhibitors
Metronidazole (bacteridical: metabolic biproducts disrupt DNA)	Metronidazole (Flagyl)	Anaerobics	Seizures Crebelar dysfunction ETOH disulfram reaction
RNA Synthesis Inhibitors
Rifampin (bactericidal: inhibits RNA transcription by inhibiting RNA polymerase)	Rifampin	Staphylococcus Mycobacterium (TB)	Body fluid discoloration Hepatoxicity (with INH)
Mycolic Acids Synthesis Inhibitors
Isoniazid	Isoniazidz	TB Latent TB
Folic acid Synthesis Inhibitors
Trimethoprim/Sulfonamides (bacteriostatic: inhibition with PABA)	Trimethoprim/Sulfamethoxazole (SMX) Sulfisoxazole Sulfadiazine	UTI organisms Proteus Enterobacter	Thrombocytopenia Avoid in third trimester of pregnancy
Pyrimethamine	Pyrimethamine	Malaria T. gondii

Bacteria Overview

Gram Postive Cocci
Staphylococcus	Staph. aureus MSSA MRSA Staph. epidermis Staph saprophyticus
Streptococcus	Strep pneumoniae Strep pyogenes (Group A) Strep agalacticae (Group B) Strep viridans Strep Bovis (Group D)
Enterococci	E. faecalis (Group D strep)
Gram Positive Bacilli
Spore Forming	Bacillus anthracis Bacillus cereus Clostridium tetani Clostridium botulinum Clostridium perfringens Clostridium difficile
Non-Spore Forming	Corynebacterium diphtheriae Listeria monocytogenes
Gram Negative Cocci
Neisseria	Neisseria meningitidis Neisseria gonorrhoeae
Gram Negative Bacilli
Enterics	Escherichia coli Salmonella typhi Salmonella enteridis Shigella dysenteriae Klebsiella pneumoniae Serratia Proteus Campylobacter jejuni Vibrio cholerae Vibrio parahaemolyticus/vulnificus Helicobacter pylori Pseudomonas aeruginosa Bacteroides fragilis
Respiratory bacilli	Haemophilus influenzae Haemophilius ducreyi Bordatella pertussis
Zoonotic bacilli	Yersinia enterocolitica Yersinia pestis Brucella Francisella tularensis Pasteurella multocida Bartonella henselae
Other	Gardnerella vaginalis
Other Bacteria
Mycobacteria	Mycobacterium tuberculosis Mycobacterium leprae MOTTS
Spirochetes	Borrelia burgdorferi Leptospira interrogans Treponema pallidum
Chlamydiaceae	Chlamydia trachomatis Chlamydophila Rickettsia Ehrlichia
Mycoplasmataceae	Mycoplasma pneumoniae Ureaplasma urealyticum
Fungus-like Bacteria	Actinomyces israelii Nocardia

Antibiotic Resistance Mechanisms

Bacteria develop ability to hydrolyze these drugs using β lactamase
- confers resistance to penicillin
- e.g. E. coli, Staph epidermidis, Pseudomonas aeruginosa, Klebsiella pneumoniae
- add β lactamase inhibitor e.g. clavulanic acid in amoxicillin-clavulanate (Augmentin)
Genetic mutation of mecA
- carried by Staphylococcal cassette chromosome (SCCmec) mobile genetic unit
- a bacterial gene encoding a penicillin-binding protein (PBP2a).
  - PBP2a has reduced affinity for antibiotics
  - confers resistance to methicillin, oxacillin, nafcillin
  - e.g. MRSA
    - SCCmec type IV has less genetic elements and is specific to CA-MRSA, making CA-MRSA less multi-drug resistant
Altered cell wall permeability
- confers resistance to tetracyclines, quinolones, trimethoprim and β lactam antibiotics
Creation of biofilm barrier
- provides an environment where offending bacteria can multiply safe from the hoste immune system
  - Salmonella
  - Staph epidermidis
Active efflux pumps
- confers resistance to erythromycin and tetracycline
- e.g. msrA gene in Staph
Altered peptidoglycan subunit (altered D-alanyl-D-alanine of NAM/NAG-peptide)
- confers resistance to vancomycin
- e.g. vancomycin resistant enterococcus (VRE)
Ribosome alteration
- erm gene confer inducible resistance to MLS (macrolide lincosamide streptogranin) agents via methylation of 23s rRNA
- demonstrate using D zone test
  - for inducible clindamycin resistance in Staph and beta hemolytic Strep

Penicillins

Mechanism
- interferes with bacterial cell wall synthesis
Subclassification and tested examples
- natural
  - penicillin G
- penicillinase-resistant
  - methicillin (Staphcillin)
- aminopenicillins
  - ampicillin (Omnipen, Polycillin)

Cephalosporins

Overview
- bactericidal
Mechanism
- disrupts the synthesis of the peptidoglycan layer of bacterial cell walls
  - does so through competitive inhibition on PCB (penicllin binding proteins)
  - peptidoglycan layer is important for cell wall structural integrity.
- same mechanicsm of action as beta-lactam antibiotics (such as penicillins)
Subclassification and tested examples
- first generation
  - cefazolin (Ancef, Kefzol)
- second generation
  - cefaclor (Ceclor)
- third generation
  - cefriazone (Rocephin)
- fourth generation
  - cefepime (Maxipime)

Fluoroquinolones

Mechanism
- blocks DNA replication via inhibition of DNA gyrase
Side effects
- inhibit early fracture healing through toxic effects on chondrocytes
- increased rates of tendinitis, with special predilection for the Achilles tendon.
  - tenocytes in the Achilles tendon have exhibited degenerative changes when viewed microscopically after fluoroquinolone administration.
  - recent clinical studies have shown an increased relative risk of Achilles tendon rupture of 3.7.
Subclassification and tested examples
- ciprofloxacin (Cipro)
- levofloxacin (Levaquin)

Aminoglycosides

Mechanism
- bactericidal
- inhibition of bacterial protein synthesis
  - work by binding to the 30s ribosome subunit, leading to the misreading of mRNA. This misreading results in the synthesis of abnormal peptides that accumulate intracellularly and eventually lead to cell death. These antibiotics arebactericidal.
Subclassification and tested examples
- gentamicin (Garamycin)

Vancomycin

Coverage
- gram-positive bacteria
Mechanism
- bactericidal
- an inhibitor of cell wall synthesis
Resistance
- increasing emergence of vancomycin-resistant enterococci has resulted in the development of guidelines for use by the (CDC)
- indications for vancomycin
  - serious allergies to penicillins or beta-lactam antimicrobials
  - serious infections caused by susceptible organisms resistant to penicillins (MRSA, MRSE)
  - surgical prophylaxis for major procedures involving implantation of prostheses in institutions with a high rate of MRSA or MRSE

Rifampin

Most effective against intracellular phagocytized Staphylococcus aureus in macrophages

Linezolid

Linezolid binds to the 23S portion of the 50S subunit and acts by preventing the formation of the initiation complex between the the 30S and 50S subunits of the ribosome

Splenectomy

Splenectomy patients or patients with functional hyposplenism require the following vaccines and/or antibiotics
- Pneumococcal immunization
- Haemophilus influenza type B vaccine
- Meningococcal group C conjugate vaccine
- Influenza immunization
- Lifelong prophylactic antibiotics (oral phenoxymethylpenicillin or erythromycin)

Please rate topic.

Average 4.4 of 60 Ratings

Questions (28)

Sorry, this question is for
PEAK Premium Subscribers only

Upgrade to PEAK

Sorry, this question is for
PEAK Premium Subscribers only

Upgrade to PEAK

Sorry, this question is for
PEAK Premium Subscribers only

Upgrade to PEAK

(OBQ18.252) A 42-year-old IV drug user presents to the emergency department with a large abscess on his forearm. A bedside I&D is performed and he is started on broad-spectrum IV antibiotics. Initial results from his cultures demonstrate methicillin-resistant Staphlycoccus aureus (MRSA) that is also resistant to erythromycin. The team would like to transition him to oral clindamycin. Prior to transitioning him to clindamycin, which additional laboratory test should be performed?

QID: 213148

Type & Select Correct Answer

Type in at least one full word to see suggestions list

Oxidase test

14%

(251/1827)

D-zone test

61%

(1111/1827)

CAMP test

14%

(249/1827)

Ziehl–Neelsen stain

(166/1827)

Etest

(31/1827)

Select Answer to see Preferred Response

SUBMIT RESPONSE 2 Review Tested Concept Review Full Topic

(OBQ18.175) Which of the following antibiotics acts to inhibit protein synthesis by preventing the formation of the initiation complex between the 30S and 50S subunits of the ribosome?

QID: 213071

Type & Select Correct Answer

Type in at least one full word to see suggestions list

Gentamicin

24%

(453/1891)

Doxycycline

14%

(263/1891)

Chloramphenicol

(124/1891)

Linezolid

39%

(729/1891)

Erythromycin

16%

(312/1891)

Select Answer to see Preferred Response

SUBMIT RESPONSE 4 Review Tested Concept Review Full Topic

(OBQ18.6) Which of the following correctly describes a class of antibiotics and its mechanism of action?

QID: 212902

Type & Select Correct Answer

Type in at least one full word to see suggestions list

Penicillins, inhibits bacterial protein synthesis

(33/1799)

Aminoglycosides, inhibits bacterial cell wall synthesis

(71/1799)

Fluoroquinolones, inhibits DNA gyrase

89%

(1607/1799)

Cephalosporins, inhibits bacterial protein synthesis

(37/1799)

Vancomycin, inhibits bacterial protein synthesis

(41/1799)

Select Answer to see Preferred Response

SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic

(SBQ18BS.7) Figures A through C are the radiographs and CT scan of a 33-year-old male who was treated 13-months ago for an open tibial shaft fracture. He has received several courses of intravenous antibiotics for chronic osteomyelitis. Despite continued treatment with IV antibiotics, his inflammatory markers remain elevated. The decision is made to proceed with irrigation and debridement, nail removal with exchange for a polymethylmethacrylate intramedullary nail with vancomycin and tobramycin. What is the primary mechanism of action of tobramycin?

QID: 211178

FIGURES:

Type & Select Correct Answer

Type in at least one full word to see suggestions list

Irreversibly binds to 30S ribosomal subunit, inhibiting bacterial protein synthesis

56%

(1001/1795)

Reversibly binds to 30S ribosomal subunit, inhibiting bacterial protein synthesis

11%

(190/1795)

Irreversibly binds to 50S ribosomal subunit, inhibiting bacterial protein synthesis

24%

(430/1795)

Reversibly binds to 50S ribosomal subunit, inhibiting bacterial protein synthesis

(93/1795)

Inhibits cell wall synthesis by binding to the D-alanyl-D-alanine precursor units

(66/1795)

Select Answer to see Preferred Response

SUBMIT RESPONSE 1 Review Tested Concept Review Full Topic

Sorry, this question is for
PEAK Premium Subscribers only

Upgrade to PEAK

(SBQ13BS.31.1) Which of the following antibiotics works by binding to the 50S ribosomal subunit?

QID: 214240

Type & Select Correct Answer

Type in at least one full word to see suggestions list

Cefazolin

(26/1730)

Ciprofloxacin

10%

(181/1730)

Clindamycin

65%

(1120/1730)

Doxycycline

19%

(333/1730)

Vancomycin

(63/1730)

Select Answer to see Preferred Response

SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic

Sorry, this question is for
PEAK Premium Subscribers only

Upgrade to PEAK

Sorry, this question is for
PEAK Premium Subscribers only

Upgrade to PEAK

Sorry, this question is for
PEAK Premium Subscribers only

Upgrade to PEAK

(OBQ12.53) What mechanism allows Staphylococcus epidermidis to adhere to surfaces and resist phagocytosis?

QID: 4413

Type & Select Correct Answer

Type in at least one full word to see suggestions list

Creation of active efflux pumps

(48/5035)

Methylation of 23s rRNA

(38/5035)

Biofilm production

93%

(4686/5035)

Alteration of cell wall permeability

(103/5035)

Beta-lactamase production

(138/5035)

Select Answer to see Preferred Response

SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic

(OBQ11.138) MecA is the bacterial gene which encodes for a penicillin-binding protein that alters the efficacy of beta-lactam antibiotics. Which of the following species of bacteria are known to produce mecA?

QID: 3561

Type & Select Correct Answer

Type in at least one full word to see suggestions list

Clostridium dificile

(20/2673)

Clostridium tetani

(12/2673)

Vancomycin-resistant enterococcus

(99/2673)

Methicillin-resistant staphylococcus aureus

93%

(2481/2673)

Streptococcus epidermidis

(47/2673)

Select Answer to see Preferred Response

SUBMIT RESPONSE 4 Review Tested Concept Review Full Topic

(OBQ11.70) Which of the following antibiotic families inhibit bacterial DNA gyrase?

QID: 3493

Type & Select Correct Answer

Type in at least one full word to see suggestions list

Quinolones

80%

(2075/2594)

Penicillins

(25/2594)

Aminoglycosides

11%

(297/2594)

Macrolides

(136/2594)

Sulfonamides

(44/2594)

Select Answer to see Preferred Response

SUBMIT RESPONSE 1 Review Tested Concept Review Full Topic

Sorry, this question is for
PEAK Premium Subscribers only

Upgrade to PEAK

Sorry, this question is for
PEAK Premium Subscribers only

Upgrade to PEAK

Sorry, this question is for
PEAK Premium Subscribers only

Upgrade to PEAK

Sorry, this question is for
PEAK Premium Subscribers only

Upgrade to PEAK

Sorry, this question is for
PEAK Premium Subscribers only

Upgrade to PEAK

Sorry, this question is for
PEAK Premium Subscribers only

Upgrade to PEAK

Sorry, this question is for
PEAK Premium Subscribers only

Upgrade to PEAK

(OBQ08.275) What is the mechanism of action of vancomycin?

QID: 661

Type & Select Correct Answer

Type in at least one full word to see suggestions list

inhibition of cell wall synthesis

80%

(2623/3299)

increase cell wall permeability

(279/3299)

ribosomal inhibition

(191/3299)

interference with DNA metabolism

(177/3299)

antimetabolite action

(19/3299)

Select Answer to see Preferred Response

SUBMIT RESPONSE 1 Review Tested Concept Review Full Topic

(OBQ06.134) Rifampin is highly effective against phagocytized intracellular Staphylococcus aureus especially in combination with other antibiotics because of its:

QID: 320

Type & Select Correct Answer

Type in at least one full word to see suggestions list

Hydrophilic activity

(98/1628)

High cell penetration

82%

(1333/1628)

Structural similarity to penicillin

(28/1628)

Structural similarity to vancomycin

(22/1628)

Beta-lactamase activity

(143/1628)

Select Answer to see Preferred Response

SUBMIT RESPONSE 2 Review Tested Concept Review Full Topic

(OBQ06.87) Which class of antibiotics inhibit early fracture healing through toxic effects on chondrocytes?

QID: 198

Type & Select Correct Answer

Type in at least one full word to see suggestions list

cephalosporins

(16/1948)

quinolones

86%

(1673/1948)

penicillins

(10/1948)

macrolides

(154/1948)

sulfonamides

(91/1948)

Select Answer to see Preferred Response

SUBMIT RESPONSE 2 Review Tested Concept Review Full Topic

(OBQ04.58) All of the following antibiotics function by interfering with protein synthesis by inhibiting ribosomes EXCEPT

QID: 1163

Type & Select Correct Answer

Type in at least one full word to see suggestions list

gentamicin

(41/2287)

tobramycin

(21/2287)

vancomycin

81%

(1863/2287)

erythromycin

(67/2287)

linezolid

13%

(289/2287)

Select Answer to see Preferred Response

SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic

(OBQ04.42) A splenectomy is performed in a 7-year-old boy following a motor vehicle accident. All of the following are recommended for long-term management EXCEPT:

QID: 103

Type & Select Correct Answer

Type in at least one full word to see suggestions list

Pneumococcal vaccination

(25/1431)

Haemophilus influenza type B vaccination

(20/1431)

Meningococcal group C vaccination

(20/1431)

Lifelong prophylactic antibiotics

46%

(654/1431)