Week 4 - Antibiotics: Inhibitors of Protein Synthesis

Question 1

Protein synthesis inhibitors.. Selective toxicity

Answer 1

Bind and inhibit prokaryotic ribosome without blocking eukaryotic ribosome

Question 2

What are the 30S inhibitors of protein synthesis?

Answer 2

30S inhibitors include aminoglycosides and tetracycline

Question 3

What are the 50S inhibitors of protein synthesis?

Answer 3

50S inhibitors include linezolid, macrolides, chloramphenicol, clindamycin, quinupristin/dalfopristin

Question 4

What are the different steps that the antibiotics inhibit during translation of mRNA to protein?

Answer 4

Initiation- linezolid, aminoglycosides Elongation- aminoglycoside, tetracycline, macrolide,chloramphenicol, clindamycin, quinupristin/dalfoprisitin Termination- aminoglycoside

Question 5

Most ribosome inhibitors are ____________?

Answer 5

Note: Most ribosome inhibitors are bacteriostatic Linezolid, tetracycline and chloramphenicol interfere with mitochondrial ribosomes (bone marrow suppression)

Question 6

What are the initiation steps of translation in prokaryotes?

Answer 6

Initiation in Prokaryotes

• Initiation factors associate with the 30S ribosomal subunit.
• Formylmethionine initiator tRNA and mRNA bind to 30S subunit.
• 50S ribosome then binds and you have the complete initiation complex.

Question 7

Where does Linezolid bind to do inhibit translation?

Answer 7

The P-site on the 50S

Question 8

Where do aminoglycosides bind to in order to inhibit translation?

Answer 8

The 30S ribosome and freezes the initiation complex

Question 9

Oxazolidinones

Mechanism

Spectrum

Resistance

Adverse Effects

Important fact

Answer 9

Linezolid Mechanism: Bacteriostatic- Inhibits protein synthesis by binding to the 23S ribosomal RNA on the 50S subunit and preventing formation of the initiation complex.

Spectrum: Reserved for treatment of drug resistant Gram+ including MRSA, Vancomycin Resistant Enterococci

Resistance: alterations or modifications in 23S ribosomal RNA It has a unique binding site on the 50S ribosome, resulting in no cross-resistance with other drug classes. (alteration of drug target on ribosome)

Adverse Effects: Bone marrow suppression, inhibits monoamine oxidase which can lead to serotonin syndrome

Important Facts: Excellent bioavailability

Question 10

What is the spectrum of oxazolidinones (Linezolid)?

Answer 10

Spectrum: Reserved for treatment of drug resistant Gram+ including MRSA, Vancomycin Resistant Enterococci

Question 11

What are the aminoglycosides?

Answer 11

gentamicin, neomycin, amikacin, tobramycin, streptomycin

Question 12

Aminogoycosides Mechanism Spectrum Resistance

Answer 12

Mechanism: Bactericidal- Prevents formation of initiation complex, causes misreading of mRNA, and induces early termination.

Spectrum: Gram- aerobic

Resistance:

Intrinsic resistance- failure of antibiotic to enter bacterial cell

Acquired resistance- Mutations on 30S ribosome or expression of ribosomal methyltransferases Acquisition of enzymes which inactivate the drug through acetylation, phosphorylation, or adenylation

Amikacin- less susceptible to enzyme inactivation and broader spectrum including Pseudomonas

Question 13

What is unique about the aminoglycoside Amikacin?

Answer 13

Amikacin- less susceptible to enzyme inactivation and broader spectrum including Pseudomonas

Question 14

What is the mechanism of action for aminoglycosides?

Answer 14

Binds to 30S ribosome

Question 15

Explain the dosing of aminoglycosides

Answer 15

Add Pic administered as single large dose:

Concentration-dependent killing and post antibiotic effects

Concentration-dependent: Concentrations are > 10 times above the MIC most effective at killing the organism (aminoglycosides are concentration dependent*)

Time-dependent: effect depends on time above the MIC (beta-lactams need to have multiple doses, they are time dependent*)

MIC - minimun inhibitory complex

Question 16

What are the adverse effects and important facts of aminoglycosides?

Answer 16

Adverse Effects:

Tubular necrosis:

nephrotoxicity- drug retained in renal cortex

ototoxicity- vestibular and auditory dysfunction teratogen- hearing loss in fetus so don’t use during pregnancy*

Facts: Drugs are small and polar excluded from CSF Uptake of Aminoglycosides is blocked by anaerobic conditions so strict anaerobes and facultative bacteria in anaerobic conditions are intrinsically resistant.

Can be synergetic with Penicillin

Poor gut absorption usually administered by IV

Gentamicin is synergentic with penicilian*

Question 17

Which of the following aminoglycoside is most effective against Serratia?

Kanamycin

Gentamicin

Netilmicin

Tobramycin

Amikacin

Answer 17

Gentamicin - has the lowest MIC from the table.

When would want to use amikacin instead of gentamicin? for Pseudomonas. Or if worried about bacteria expressing the enzymes that … the aminoglycosides..

Question 18

Aminoglycoside antibiotics are:

Bactericidal for Gram-positive bacteria

Modified by methyltransferases

Bind to the 50S ribosomal subunit

Time-dependent inhibitors Require bacterial growth to be effective

Answer 18

f

Question 19

What are the steps in chain elongation of proteins?

Answer 19

1. Aminoacyl tRNA is inserted in the acceptor site. Tetracyclines interfere here and prevent aminoacyl tRNA attachment to the acceptor site.
2. The peptide bond is formed. Chloramphenicol inhibits peptide bond formation.
3. fmet tRNA is released from the P site. In prokaryotes, an exit site called the E site binds tRNA after it’s displaced from the P site
4. Translocation. A dipeptide tRNA moves from the A to the P site and the ribosome moves one codon along the mRNA. Macrolides, Streptotagmins, Clindamycin inhibit translocation.
5. Another amino acyl tRNA is put in the A site and elongation continues.

Question 20

What do tetracyclines interfere with during chain elongation?

Answer 20

Tetracyclines interfere here and prevent aminoacyl tRNA attachment to the acceptor site.

Question 21

What does chloramphenicol inhibit during chain elongation?

Answer 21

Chloramphenicol inhibits peptide bond formation.

Question 22

What do macrolides, streptotagmins, and clindamycin inhibit during chain elongation of proteins?

Answer 22

Macrolides, Streptotagmins, Clindamycin inhibit translocation

Question 23

Tetracyclines- tetracycline, doxycycline, minocycline

Mechanism

Spectrum

Resistance

Answer 23

Mechanism: Bacteriostatic-bind 30S preventing attachment of aminoacyl-tRNA

Spectrum: Broad initially but due to resistance only a few: B. burgdorferi, H. pylori (alsers), Mycoplasma pneumoniae.

Resistance: Intrinsic: decreased uptake

Acquired: Increased efflux* Alteration of ribosomal target Rarely enzymatic inactivation of drug (acetyl)

Question 24

What are adverse effects of tetracyclines?

Answer 24

Adverse effects: form stable chelates with a number of metal ions such as calcium, magnesium, iron and aluminum decreasing gut absorption of the drug.

Gastrointestinal irritation and photosensitivity (abnormal sunburn reaction)

Discoloration of teeth and inhibits bone growth in children.

Pregnancy class D (should not be used)*

Question 25

Which of the following antibacterial drugs, that we discussed previously, should not be consumed with milk or antacids due to the formation of an insoluble complex between the drug and cations

A. Nitrofurantoin

B. Ciprofloxacin

C. Metronidazole

D. Penicillin G

E. Rifampin

Answer 25

B. Ciprofloaxacin - fluoroquinolones class

Question 26

What is mycoplasma pneumonia?

Answer 26

atypical pneumonia

Use: Doxycycline, Azithromycin, Levofloxacin

Beta-lactams are not effective* (no cell wall)

Question 27

A 32-year-old woman has a 6 day history of fever and fatigue. She recently noticed an unusual rash on her leg that has spread rapidly prompting her to see her physician. She lives in a wooded area outside of Moose Lake. What’s your diagnosis and the causative agent?

Use the John Hopkin’s guide to find the recommended antibiotics for early treatment of the
disease

Answer 27

Lymes Disease

Tic is injecting the bacteria Borrelia burgdorferi into the human

Johs hopkins guide: Amoxicillian or Doxycyclines

Question 28

Chloramphenicol

Mechanism

Spectrum

Resistance

Answer 28

Mechanism: Bacteriostatic- binds 50S preventing peptide bond formation- peptidyltransferase can’t associate with amino acid substrate

Spectrum: Extended but use is limited due to severe side effects Resistance: acetyltransferase modifies drug to prevent binding to the ribosome

Resistance: acetyltransferase modifies drug to prevent binding to the ribosome

Question 29

What are the adverse effects of chlormphenicol?

Answer 29

Adverse effects: TOXIC Bone marrow depression and aplastic anemia

Gray baby syndrome- premature infants lack the enzyme UDP-glucuronyl transferase and have decreased renal function so high levels of the drug accumulate, which can lead to cardiovascular and respiratory collapse

Question 30

What is grey baby syndrome?

Answer 30

Gray baby syndrome- premature infants lack the enzyme UDP-glucuronyl transferase and have decreased renal function so high levels of the drug accumulate, which can lead to cardiovascular and respiratory collapse

Question 31

What are the macrolides?

Answer 31

Macrolides- erythromycin, azithromycin, clarithromycin

Question 32

Macrolides Mechanism Spectrum

Answer 32

Mechanism: Bacteriostatic Inhibits translocation by binding 23S rRNA of the 50S subunit

Spectrum: Broad coverage of respiratory pathogens, Chlamydia

Question 33

Macrolides Resistance Adverse effects

Answer 33

Resistance: methylation of 23S rRNA binding site- also associated with clindamycin and quinupristin/dalfopristin resistance increased efflux hydrolysis of the the macrolide by esterases

Adverse effects: GI discomfort, Hepatic failure, and Prolonged QT interval

Inhibitors of cytochrome P450 enzymes (check with other medications)

Clarithromycin is not safe during pregnancy*

Question 34

Lincosamide

Mechanism

Spectrum

Resistance

Adverse effects

Answer 34

Lincosamide: Clindamycin Mechanism: Bacteriostatic- blocks translocation at 50S ribosomal subunit

Spectrum: Gram positive including anaerobic. Treat acne.

Resistance: mutation of ribosome, methylation of ribosomal RNA, Cross resistance with macrolides and streptogramins inactivation of drug by adenylation

Adverse effects: Hypersensitivity: rash and fever Diarrhea, abdominal pain, mucus and blood in stool

Superinfection with C. difficile*

Question 35

What are the streptogramins?

Answer 35

Quinupristin/Dalfopristin

Question 36

Streptogramin

Mechanism

Spectrum

Resistance

Adverse Effects

Answer 36

Quinupristin/Dalfopristin

Mechanism: Combined action is bactericidal for some organisms. Binds 50S to inhibit translocation.

Spectrum: Quinupristin/dalfopristin should be reserved for infections caused by multiple drug-resistant G+ bacteria*

Resistance: Ribosomal methylase prevents binding of drug to its target. Enzymes inactivate the drugs. Efflux proteins that pump them out of the cell. Cross resistance with macrolides and clindamycin.

Adverse Effects: High incidence including arthralgias and myalgias are common. Inhibits a cytochrome P450 enzyme and is likely to have significant drug interactions.

Question 37

Review: Write the mechanism of action for the following inhibitors include where the drug binds and resistance

Name specific agents for Aminoglycosides, Tetracyclines, Macrolides, Streptogramins Linezolid Aminoglycosides Tetracyclines Chloramphenicol

Answer 37

Linezolid - Bacteriostatic. inhibits protein syntheis, binds to 50S ribosomal subunit. Resistance - alterations of UNIQUE binding site (no cross resistace)

Aminoglycosides - Bactericidal. Prefents initiation complex inducint early termination (multiple steps inhibited - thats whey bactericidal). Resistance - failur to enter cell. Mutations of 30S, bacterial enzymes,

Tetracyclines - Bacteriostatic. Bind to 30S preventing attachment of tRNA. Reistance - decreased uptake (alteration of target site). Increased efflux*

Chloramphenicol - Bacterio static - binds to 50S. prevents protein formation. Resistance - Modifies drug to prevent binding

Question 38

Write the mechanism of action for the following inhibitors include where the drug binds and resistance

Name specific agents for Aminoglycosides, Tetracyclines, Macrolides,

Answer 38

Aminoglycosides

Tetracyclines

Mactrolides

Streptogramins

Question 39

Enterococcus Resistance

Answer 39

Question 40

A 42 year old male presents with a ruptured appendix and peritonitis resulting in severe infection with both aerobic and anaerobic Gram negative organisms. Why is monotherapy with an aminoglycoside inappropriate? What drugs are effective against anaerobic organisms?

Answer 40

Why is monotherapy with an aminoglycoside inappropriate?

-Because it needs energy to enter cell so it would not cover the anaerobic microbes

What drugs are effective against anaerobic organisms?

Vancomycin

Metrozonol

Question 41

Which of the following contributes to gray baby syndrome when chloramphenicol is administered to neonates?

Decreased intestinal absorption

Increased glomerular filtration

Lack of CNS penetration

Alteration of gastrointestinal flora by a broad spectrum antibiotic

Low hepatic glucuronyl transferase activity

Answer 41

Low hepatic glucuronyl transferase activity.. babys do not have this enzyme…

Question 42

Treatment of a bacterial culture with an antibacterial drug results in the cytoplasmic accumulation of monosomes (have block before 50S is added so only get one ribosome subunit on the mRNA). The antibacterial drug is most likely:

Amikacin

Azithromycin

Ciprofloxacin

Meropenem

Tetracycline

Answer 42

Amikacin - it blocks the formation of the inititation complex (binds to 30S subunit)

Question 43

Your initial treatment with tetracycline is ineffective so you switch to erythromycin. Unfortunately, your patient still doesn’t respond to the new therapy. This is mostly likely because of resistance due to:

Enzymatic degradation of the drugs

Active efflux of the drugs from the bacteria by a transporter

Modification of the 50 S ribosomal subunit by methyltransferase preventing binding of the drugs

Acetylation of the drugs

Overproduction of the ribosomal target

Answer 43

Active efflux of the drugs.

It is not C because they both do not bind to 50S, one binds to 50 the other to 30

Question 44

NB is a 21-year-old college football player (linebacker) who presents to the clinic with a large, red abscess on his right arm, likely due to community-acquired methicillin-resistant Staphylococcus aureus. It is lanced and drained, and antibiotic therapy is to be prescribed. Which drug would be the most appropriate choice for NB’s infection? He is to be treated as an outpatient.

A. Cephalexin

B. Ciprofloxacin

C. Erythromycin

D. Vancomycin

E. Linezolid

Answer 44

Linezolid - Can also be used for MRSA

Vanco is good but it is bad for oral (out pt)

Question 45

Identify the drugs that are reserved for infections due to hard to treat drug resistant bacteria like MRSA and VRE (vancomycin resistant enterococcus)

Answer 45

5th gen cephalosporin- ceftaroline, vancomycin, TMP-SMX, daptomycin, Quinupristin-Dalfopristin, Linezolid

Question 46

Your patient has a suppressed immune system which of the following antibiotics is the best choice for your patient.

A. Doxycycline

B. Gentamicin

C. Erythromycin

D. Linezolid

E. Clindamycin

Answer 46

B - Gentamicin

It is bacteriocidal… not bacterial static

Bacterial static drugs rely on immune system to come and take up the bacteria after their replication has been inhibited becasue they are not dead yet..

Question 47

A 30 year old woman who is pregnant has a severe lung infection. She needs to be treated with an antibiotic. Assume each of the following is effective against the bacteria in question. Which would you choose?

Azithromycin

Clarithromycin

Gemifloxacin

Minocycline

Moxifloxacin

Answer 47

A. Azithromycin

Mox and gem are fluoroquinolones

Minocyclin is bad on teeth

Azith and clari are in same class but clarith is bad for prego.

Question 48

Identify the antibiotics for the following:

Dont use with newborns

Dont use in children

Dont use during pregnancy

In the elderly, adjust for reduced renal function

Answer 48

Don’t use with Newborns Chloramphenicol (can’t glucuronidate) Erythromycin (pyloric stenosis)

Don’t use in children Tetracyclines, Fluoroquinolones

Don’t use during Pregnancy Tetracycline, Aminoglycosides, Clarithromycin, Fluoroquinolones, Chloramphenicol

In the elderly, adjust for reduced renal function. The half life of beta lactams, aminoglycosides and fluoroquinolones will be increased.

Question 49

What are antibiotics that may cause hemolysis in patients with glucose-6-phosphate dehydrogenase deficiency?

Answer 49

Sulfonamides (Trimethoprim/Sulfamethoxazole). It will cause hemolysis..

Question 50

A 23-year old female is being treated for a severe infection in the hospital. Every time she gets up and attempts to move around her room, she loses her balance. The antibiotic treatment that is most likely responsible for her symptom is:

Gemifloxacin

Linezolid

Piperacillin

Quinupristin/ dalfopristin

Tobramycin

Answer 50

E. Tobramycin - kidney and otto imbalances…

Question 51

What antibiotics are associated with the following?

Seizures

Hepatotoxicity

Nephrotoxicity

Ototoxicity

QTc interfal prolongation

Anemia

Arthralgia

Disulfiram

Superinfection

Answer 51

Seizures: beta-lactams (particularly carbapenems) Hepatotoxicity: Rifampin Nephrotoxicity: Sulfonamides, Aminoglycosides, Vancomycin Ototoxicity: Aminoglycosides, Vancomycin QTc interval prolongation: macrolides, fluoroquinolones Anemia: Chloramphenicol, Trimethoprim Arthralgia: Quinupristin/dalfopristin, Fluoroquinolones Disulfiram-reaction when taken with alcohol: metronidazole,2nd gen Cephalosporin with methylthiotetrazole groups Superinfection: Clindamycin, fluoroquinolones, 3rd gen Cephalosporin, Ampicillin

Question 52

Sulfonamides Patients should not be given other sulfa drugs such as diuretics Beta-lactam Skin test can be used to confirm and patient can be desensitized Clindamycin Which of the following beta-lactams is least likely to cause an allergic reaction?

A. Aztreonam

B. Penicillin

C. Cephalosporin

D. Carbapenem

Answer 52

Aztreonam

Question 53

What antibiotics have drug-drug interactions?

Answer 53

Rifampin induces drug metabolizing enzymes

Clarithromycin and Erythromycin inhibit hepatic metabolism

Question 54

Combination drug therapy:

Answer 54

1. Enhancement of antibacterial activity in the treatment of specific infections (synergism) Trimethoprim – Sulfamethoxazole Inhibits multiple steps in folate synthesis Aminoglycoside + Penicillin Penicillin increases permeability of cell membranes increasing the ability of aminoglycosides to enter the cell
2. Treatment of mixed bacterial infections caused by two or more microbes.
3. Therapy of severe infections in which a specific etiology is unknown. Not to be used as a shortcut but used until clinical and lab data allow the selection of a specific antimicrobial
4. Prevention of the emergence of resistant organisms. Treatment of Tuberculosis
5. Addition of inhibitors to prevent degradation of the enzyme Ampicillin-sulbactam, Amoxicillin-clavulanate, Piperacillin-tazobactam, Ticarcillin-clavulanate Imipenem-cilastatin (blocks renal dehydropeptidase)

Question 55

What are the drawbacks of using drugs in combination?

Answer 55

1. Risk of toxicity from two agents Vancomycin or Aminoglycosides each alone have some nephrotoxicity. If given together you get marked renal impairment.
2. Antagonism Pneumococcal meningitis Penicillin - 21% mortality Penicillin + Tetracycline - 79% mortality
3. Selection of microorganisms resistant to antibiotics
4. Superinfection
5. Extra cost

Question 56

What are the guidlines for effective treatment?

Answer 56

Avoid using antibiotics to treat colonization of contamination

Goal to use narrow-spectrum agent that is effective

Use the proper dose if exposed to low concentrations that don’t kill more likely to develop resistance

Use the shortest effective duration of therapy

Question 57

Prokaryote vs Eukaryote Ribosome differences

Answer 57

Prokaryote: 30S and 50S start with formyl methionine - AUG Shine Delgarno sequence Eukaryotes 40S and 60S Start with methionine - AUG and 5’ cap

Question 58

How do bacteria become resistant to vancomycin?

Answer 58

Changes the end of the aminoglycan sugar group? look this one up.

Question 59

Which of the following is true regarding aminoglycosides?

Bactericidal for gram-pos

modifiec by methyltranferases

bind to 50S ribosomal subunit

Time-dependent inhibitors

require energy to be effective

Answer 59

Bacterialcidal with pennicilian

Enzyme inhibitors

Bind to 30S

It is a concentration depentent inhibitor (get hight does above MIC vs just being above the MIC for a long time)

Yes. E.

Question 60

Steps to prescribe antibiotics…

Answer 60

Step 1: Identify the type of infection. Where and what organism?
Symptoms- key, subjective effects felt by patient like pain
Signs are objective evidence-rash
Time course- bacterial meningitis is acute vs.
fungal meningitis may take a few weeks.
Diagnostic tests- often incorporate properties of organisms
Epidemiology- organisms most likely to infect particular age group as well risk factors like HIV status, tick exposure

Step 2: Where and how is the person infected?
Transmission
Microbiology organism virulence factors evade host defense
Pathology damage to the host and possible sequelae associated with this organism

Step 3: How should the infection be managed?
Prevention: strategies to inhibit transmission
Mechanism & Spectrum: how do antimicrobials work and what organisms are they effective against
Pharmacology: ADME, Need a drug that can get to the microorganism
Patient factors: Pregnant, immunocompromised
Is the organism resistant against certain antibiotics?