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Pharmacology > Lecture 15 - Antibiotics 2 > Flashcards

Lecture 15 - Antibiotics 2 Flashcards

1
Q

What are the most commonly prescribed antibiotics?

A 
30% cell wall inhibitors
-penicillins, cephalosporins
34% protein synthesis inhibitors
-tetracyclines, macrolides
12% DNA synthesis inhibitors
-fluoroquinolones
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2
Q

Describe cell wall inhibitors

A
  • bacteria have cell walls
  • mammalian cells do not have cell walls
  • targeting the synthesis of bacterial cell walls is one of the most widely effective and least toxic antibiotic strategies
  • only effective against actively growing bacteria
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3
Q

Examples of cell wall inhibitors

A
  • penicillins

- cephalosporins

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4
Q

Describe Penicillin

A
  • Blocks the last step of bacterial cell wall synthesis
  • Inhibits “transpeptidases” that form cross-links between peptidoglycan chains that are essential for cell wall integrity
  • Causes osmotic pressure on the cells resulting in cell lysis
  • Gram positive bacteria produce enzymes called “autolysis” that break down the cell wall
  • Without active cell wall synthesis autolysis can damage the cell

*Blocks the cross-links, allows things to penetrate through the cell wall and kill the microbe

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5
Q

List the types of Penicillins

A
  • Penicillin G, Penicillin V
  • Penicillinase-resistant penicillins
    • Methicillin, cloxacillin
  • Extended spectrum penicillins
    • Ampicillin, amoxicillin
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6
Q

List 3 important facts about Penicillins

A

Bactericidal
Cross resistance
Cross allergic potential

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7
Q

Administration of penicillins

A

Route is determined by stability of the medicine to gastric acid and the severity of the infection:

  • Penicillin V, Amoxicillin only available as oral preparations
  • Piperacillin must be by the IV/IM route
  • Others available as oral, IV, IM preparations
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8
Q

Absorption of penicillins

A

Most penicillins are incompletely absorbed so they affect the composition of the intestinal flora
-Absorption of penicillinase Resistant antibiotics are reduced by food in the stomach and must be administered before a meal or 2-3 h after

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9
Q

Distribution of penicillins

A

Distribution is throughout the body

-crosses the placenta but does not penetrate bone or CNS

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10
Q

Excretion of penicillins

A

in the urine and breast milk

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11
Q

Adverse Effects of Penicillins

A
  • GI effects relatively common but seldom severe due to disruption of normal intestinal microflora
  • Allergy to its metabolite penicillin acid relatively common (rash, swelling of tongue/lips, anaphylaxis)
  • Cross allergy within penicillin class
  • Hematological: reduced coagulation a concern in patients receiving anticoagulants
  • No teratogenicity
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12
Q

Cephalosporins have a similar ____ and ______ to penicillins

A

structure

mechanism

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13
Q

List some cephalosporins

A

cephalexin
cephalothin
cepazolin
cefepime

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14
Q

Administration of cephalosporins?

A

Most must be administered IV/IM due to poor oral absorption:

-Cephalexin and Cefixime are administered orally

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15
Q

Distribution of cephalosporins?

A

Throughout the body

  • Cefazolin penetrates the bone
  • Cefuroxime crosses the BBB
  • Cefotaxime, Ceftriaxone penetrate the cerebrospinal fluid
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16
Q

Excretion of cephalosporins?

A
  • Most are eliminated in the urine

- Ceftriaxone is excreted in the bile, longest half-life of all cephalosporins (6-8 hours) permits once a day dosing

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17
Q

Cephalosporins have cross resistance and cross allergic potential with ?

A

each other and with penicillins

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18
Q

Other adverse effects?

A

Allergy and GI effects less common than with penicillins

19
Q

Describe Protein Synthesis Inhibitors

A
  • Mammalian cells have 80S ribosomes (60S and 40S subunits)
  • Bacteria have smaller 70S ribosomes (50S and 30S subunits)
  • Protein synthesis inhibitors bind to 70S ribosomes (as opposed to 80S ribosomes)
  • Effective against gram positive and gram negative bacteria as well as other microorganisms (very broad spectrum)

*they inhibit peptide synthesis

20
Q

Examples of Protein Synthesis Inhibitors

A
  • Tetracyclines
  • Aminoglycosides
  • Macrolides
  • Chloramphenicol
  • Clindamycin
21
Q

Describe Tetracyclines

A
  • Binds irreversibly to the 30S ribosome
  • Blocks acyl-tRNAaccess to the ribosome
  • Broad spectrum
  • Bacteriostatic
22
Q

What is the naturally occurring tetracycline?

A

Tetracycline

23
Q

What is the semi-synthetic tetracyclines?

A
  • Doxycycline
  • Methacycline
  • Minocycline
24
Q

Administration of Tetracyclines?

A

Oral route is determined by stability of the medicine to gastric acid and the severity of infection

25
Q

Absorption of Tetracyclines?

A

Adequately but incompletely absorbed orally:

  • Absorption is reduced by consumption of dairy foods
  • Antacids also poorly reduce absorption
26
Q

Distribution of tetracyclines?

A

Is throughout the body and body fluids:

  • concentrates in liver, kidney and spleen
  • crosses the placenta and penetrates bone and teeth
27
Q

Excretion of Tetracyclines?

A

Metabolized and conjugated to form glucuronides by the liver and secreted in the bile and enters the urine via glomerular filtration:
-Excreted by breast milk

28
Q

Adverse Effects of Tetracyclines?

A
  • GI discomfort - overcome by consuming food with the pills
  • Deposition in bones and teeth of growing children (also a concern with elders)
  • Hepatotoxicity
  • Sunburn - increased sensitivity to UV rays
  • Dizziness, nausea, vomiting (minocycline, doxycycline concentrate in the inner ear)
  • Headache/blurred vision
  • Superinfectins: resistance is common
  • Not recommended for patients with kidney/liver disease or pregnant/lactating women
29
Q

Describe Aminoglycosides

A
  • Binds irreversibly to the 30S ribosome
  • Blocks functional assembly of the ribosome
  • Effective against aerobic gram negative bacteria
  • Bactericidal
30
Q

Aminoglycosides derived from Streptomyces?

A
  • Streptomycin

- Kanamycin

31
Q

Aminoglycosides derived from Micromonospora?

A
  • Gentamicin

- Amikacin

32
Q

Administration of Aminoglycosides?

A

IV/IM, some are used topically:

-Molecular properties prevent oral absorption

33
Q

Distribution of aminoglycosides?

A

Is throughout the body:

  • Levels achieved in most tissues are low
  • Concentrates in renal cortex and inner ear
  • Low penetration into cerebrospinal fluid
  • Crosses the placenta and enters fetal circulation
34
Q

Excretion of aminoglycosides?

A

in the urine

35
Q

Adverse effects of aminoglycosides?

A
  • Nephrotoxicity - retention of aminoglycosides by proximal tubular cells disrupts calcium-mediated transport: ranges from mild to irreversible, the elderly and individuals with kidney disease are most susceptible
  • Ototoxicity - deafness caused by the destruction of hair cells within the inner ear (fetuses and the elderly are most susceptible)
  • Neuromuscular paralysis - high dose toxicity from injections (Prompt calcium gluconate or neostigmine application can reverse paralysis)
  • Allergic reactions - contact dermatitis from topical neomycin applications
36
Q

Describe Macrolides

A
  • Binds irreversibly to the 50S ribosome
  • Blocks peptide transfer
  • Broad spectrum, effective against gram positive bacteria
  • Bacteriostatic, bactericidal at high doses
37
Q

Macrolides derived from Streptomyces?

A
  • Erythromycin
  • Clarithromycin
  • Azithromycin
38
Q

Macrolides known as synthetic “ketolides” ?

A

Telithromycin

39
Q

Administration of Macrolides

A

Oral

-Azithromycin available for IV infusion

40
Q

Absorption of Macrolides

A
  • Adequate, but food interferes with absorption

- Erythromycin is destroyed by gastric acid so tablets must be enteric coated

41
Q

Distribution of Macrolides

A

Is throughout the body:

  • Does not penetrate into cerebrospinal fluid
  • Concentrates in the liver
42
Q

Excretion of the Macrolides

A

In the bile:

-Inactive metabolites secreted in the urine

43
Q

Adverse effects of Macrolides

A
  • GI problems (most common side effect)
  • Jaundice (patients with liver disease should not be treated with macrolides since they accumulate in the liver)
  • Ototoxicity (transient deafness associated with high dose erythromycin)
  • Prolonged QTc interval - patients with existing arrhythmias (associated with erythromycin, clarithromycin, telithromycin paralysis)
  • Myopathy - Interactions with statins (Due to inhibition of CYP 3A4 by clarithromycin and erythromycin

Pharmacology (21 decks)

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