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Protein Synthesis Inhibitors Flashcards

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1
Q

Why is it interesting and also scary that MRSA resistant?

A

Methicillin is an antibiotic that is stable to a beta-lactamase producing organism so if something is resistant to methicillin it can be very dangerous because it means it is resistant to something that typically works against bugs that are resistant.

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2
Q

Why is Mycoplasma Pneumoniae resistant to penicillins and cephalosporins?

A

Because it lacks a peptidoglycan cell wall, not because it produces beta-lactamase. (penicillins and cephalosporins are inhibitors of cell wall synthesis - they will have no effect on this organism).

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3
Q

What do protein synthesis inhibitors target?

A

target the bacterial ribosome within the cell, not the cell wall.

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4
Q

What is the bacterial ribosome?

A

It has a smaller (70S) than the mammalian ribosome which is 80S -> it is composed of 50s and 30s subunits as opposed to 60s and 40s in humans -> so protein synthesis inhibitors won’t effect human ribosomes, it’s selective.

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5
Q

Protein Sythesis Inhibitors

A

tetracyclines
macrolides
chloramphenicol (ind. drug)
clindamycin (ind. drug).

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6
Q

Class of Tetracyclines

A

tetracycline: prototype, hardly used
doxycycline: Super important!!!
minocycline: acne
demeclocycline

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7
Q

MOA of Tetracyclines

A

Binds to 30s subunit of bacterial ribosome, believed to block access of amino acyl-tRNA to mRNA-ribosome complex at the acceptor site, thus inhibiting bacterial protein synthesis.

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8
Q

Spectrum of Tetracyclines

A

Broad spectrum: active against many gram positive and gram negative organisms including anaerobes.

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9
Q

Resistance to Tetracyclines

A
  • any organism resistant to one tetracycline is resistant to all tetracyclines
  • cell develops efflux pumps (pumps drug out of cell)
  • forms ribosomal protection proteins
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10
Q

Absorption of Tetracyclines

A

all tetracyclines adequately but incompletely absorbed thru oral ingestion

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11
Q

What decreases absorption?

A

dairy foods (less of a problem with doxy)

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12
Q

Distribution of Tetracyclines?

A

concentrate in liver, kidney, spleen, and skin and bind to tissues undergoing calcification –> teeth and bones

  • Doesn’t penetrate CSF
  • All cross placental barrier and concentrate in fetal bones and dentition
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13
Q

Elimination of tetracyclines

A

concentration in liver -> metabolized and conjugated–> released in bile –> reabsorbed in intestine and enter urine via glomerular filtration (doxy -> bile and into feces)

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14
Q

What makes doxycycline an acceptable drug for renally compromised patients/

A

Because instead of being filtered by the kidneys it stays in bile and is excreted into the feces.

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15
Q

Adverse effects of Tetracyclines?

A

Calcified tissues: deposition in the bone and primary dentition occurs during calcification of growing children -> causes discoloration and hypoplasia of teeth and temporary stunting of bones for growth.

Gastric discomfort: controlled if taken with foods other than dairy products.

Phototoxicity: severe sunburn can occur when the patient taking a tetracycline is exposed to sun or UV rays

Vestibular problems: dizziness, nausea, and vomiting occur with minocycline.

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16
Q

CI’s of Tetracyclines

A

pregnant women (category D)
Breast feeding women
Children

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17
Q

Tetracyclines routes of administration

A

Oral, IV, IM (not recommended b/c of pain and inflammation at injection site).

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18
Q

Tetracycline uses

A

STDs, atypical pneumonia, exacerbations of chronic bronchitis, acne vulgaris, and great alternative for sinusitis and acute prostatitis

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19
Q

Why do you never use tetracyclines for skin infections?

A

Because of decreased activity against staph aureus

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20
Q

Doxycycline uses:

A

DOC for mycoplasma pneumonia, chlamydiae (resp for variety of STI’s), rickettsiae (Rocky Mountain Spotted Fever), and excellent for Lyme Disease

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21
Q

Minocycline uses

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A

acne vulgaris (rarely anything else)

22
Q

Demeclocycline uses

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A

Tx of SIADH because of its inhibiting action of ADH.

*SIADH= syndrome of inappropriate antidiuretic hormone secretion

23
Q

What are the 3 macrolides?

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A

erythromycin: first one in drug class and prototype, not used nearly as much any more.

azithromycin (Zithromax): most popular macrolide, used extensively in a variety of circumstances.

Clarithromycin (Biaxin)

24
Q

Macrolides MOA

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A

bind irreversibly to a site on the 50S subunit of bacterial ribosome, thus inhibiting the translocation steps of protein synthesis

  • Bacteriostatic
25
Are macrolides stable against b-lactamase producing organisms?
yes, because they are protein inhibitors not cell wall inhibitors
26
Erythromycin spectrum
effective against same organisms as PCN G -> used in pts allergic to penicillins. Also effective against chlamydial species and mycoplasma pneumoniae and legionella pneumophila
27
Clarithromycin (Biaxin) spectrum
similar to erythro but also effective against H> influenzae (community acquired pneumonia) * Use instead of Azithro -> new trend
28
Azithromycin (Zithromax) spectrum
less active against strep and staph than erythro but more active against respiratory infections due to H. influenzae and Moraxella catarrhalis. Excellent for urethritis caused by Chlamydia trachomatis
29
Resistance to macrolides?
most strains of staph in hospital isolates are resistant to erythro clarithro and azithro show cross resistance to erythro *Not good in skin coverage -> don't use for staph aureus (MRSA)
30
Resistance mechanisms to Macrolides
alteration in the binding site of the ribosome. manifestation of an efflux pump to get the drug out of the cell. Enzymatic inactivation
31
Absorption of Macrolides
Erythro: destroyed by gastric acid and therefore need enteric coated tablet, adequately absorbed on oral administration Clarithro and Azithro: stable to stomach acid and readily absorbed
32
Distribution of Macrolides
widely distributed in tissue except for CSF
33
Metabolism of Macrolides
Erythro: cytochrome P450 drug Clarithro: metabolized by liver and may also interfere with other drugs Azithro: not a p450 drug and tends to have few interactions with other meds
34
Excretion of Macrolides
Erythro and azithro primarily concentrated in the bile Clarithro and its metabolites are eliminated by kidney and liver -> recommended that dosage be adjusted in pts with compromised renal function
35
Common adverse effects of Macrolides
GI distress including diarrhea big problem with erythro -> leads to poor pt compliance (sometimes used for constipation even) Azithro and Clarithro are much better tolerated in GI Ototoxicity: transient deafness has been associated with erythromycin especially at high dosages. prolonged QT with erythro and clarithro (rare)
36
Why is Azithro preferred over erythro and clarithro?
Fewer adverse effects fewer drug interactions don't have to worry about adjusting dose with kidney and liver disease unless severe Long half life -> easy to use and pts are more compliant (daily dosing compared to 2x daily or 4x daily)
37
Are Macrolides good for staph disease?
Nope, not good for staph just like doxycycline
38
Why are macrolides liked for tx of chlamydial cervicitis and urethritis STI's compared to doxy?
because it works really well against chlamydial species | - only have to dose single 1 gram versus a 7-10 day course of doxy
39
When are macrolides DOC?
Excellent for broad spectrum coverage of both typical and atypical pneumonias, used all the time for exacerbations of chronic bronchitis in the patient with COPD - used first line alt. for group A strep pharyngitis (strep throat)
40
Chloramphenicol -> should we use?
Active against wide range of gram + and gram - organisms but because of its HIGH toxicity, its use is restricted to life-threatening infections in which there are no alternatives!!
41
MOA of chloramphenicol
Binds to bacterial 50S ribosomal subunit and inhibits protein synthesis at the peptidyl transferase reaction
42
Spectrum of Chloramphenicol
very broad -> including anaerobes | - not effective against pseudomonas or chlamydiae
43
Pharmacokinetics of Chloramphenicol
completely absorbed orally | Readily enters CSF
44
Adverse effects of Chloramphenicol
- Hemolytic anemia - aplastic anemia --> idiosyncratic and usually fatal, occurs independent of dose and may occur after therapy has ceased! - Gray Baby syndrome -> because of interference with human mitochondrial ribosomes, can lead to poor feeding, depressed breathing, cardiovascular collapse, cyanosis, and death - can interfere with a number of other drugs
45
Clindamycin MOA
same as macrolides --> bind to 50s subunit of bacterial ribosome.
46
Clindamycin spectrum
great coverage against anaerobic bacteria but also active against many gram + cocci: staph and strep
47
Clindamycin absorption and distribution
well absorbed orally, distributes well into all body fluids except CSF
48
What is always resistant to clindamycin?
Clostridium difficile -> which is a bug that hangs out in gut and is usually harmless but with the administration of Clindamycin there can potentially be overgrowth of C. difficile which can lead to potentially fatal disease --> pseudomembranous colitis with side effects of diarrhea, nausea, and skin rash
49
What are the common meds used against anaerobes?
Clindamycin or Metronidazole (Flagyl) | - Excellent in treating infections of the gut and used to treat penetrating wounds of abdomen and gut
50
What should you think of when you hear anaerobic infection?
gut flora or female genital tract flora

Infectious Disease (27 decks)

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