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Medicine 2 - 03 Pneumonia > 4 Pharmacology of Antibiotics > Flashcards

4 Pharmacology of Antibiotics Flashcards

1
Q

Describe features of gram Positive bacteria

A
  • Lack outer membrane
  • Thick cell wall - 15-50nm thick
  • Made of peptidoglycan (50%) and acid polymer (40-45%)
  • Highly charged (streptococci, staphylococci)
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2
Q

Describe features of gram Negative bacteria

A
  • They have a complex liposaccharide outer membrane
  • Complex outer layer makes it more resistant to antibiotics (pseudomonas aeruginosa)
  • And thinner cell wall (than gram +ve)
  • Peptidoglycan layer 2nm and 5% of cell mass
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3
Q

List some common gram-positive bacteria

A
  • Staph. aureus
  • Strept. pneumoniae
  • Clostridium botulinum
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4
Q

List some common gram-negative bacteria

A
  • Escherichia coli (E. coli)
  • pseudomonas aeruginosa
  • Acinetobacter baumanii
  • Haemophilus influenzae
  • Neisseria gonnorhoeae
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5
Q

Describe the principles of antibiotic chemotherapy

A

There are different ways of classifying antibiotics:

  • Bacteriostatic antibiotics (stop the growth of bacteria)
  • Bactericidal antibiotics (kill bacteria)
  • Broad-spectrum antibiotics (act against a wide range of bacteria - like on gram +ve and -ve; e.g. Amoxicillin)
  • Narrow-spectrum antibiotics (act against specific bacteria - are targeted e.g. Vancomycin)
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6
Q

List the categories of antibiotics

which target different aspects of a bacteria

A
  • Cell wall synthesis inhibitors
  • Cell membrane integrity disruptors
  • Protein synthesis and nucleic acid inhibitors
  • Metabolic pathway inhibitors
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7
Q

List the different types of cell wall synthesis inhibitors and cell membrane integrity disruptors

A
  • Beta-lactams

- Glycopeptides

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8
Q

Name the different types of Beta-lactam antibiotics

A
  • Penicillins
  • Cephalosporins
  • Carbapenems
  • Monobactams
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9
Q

Describe the principle by which bacterial cell walls are made up of

A

Bacterial cell walls are made up of alternating amino sugar units of:

  • N-acteylglucosamine (NAG)
  • N-acetylmuramic acid (NAMA)

The NAMA has a short peptide side chain that is cross-linked using an enzyme called TRANSPEPTIDASE to from a polymeric lattice

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10
Q

State the mechanism of action of Beta-lactams

A

Beta-lactams target bacterial cell wall synthesis:
- by binding irreversibly to a transpeptidase, thus preventing cross-links peptidoglycans in the bacterial cell wall being made

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11
Q

Describe penicillin

A

It is a type of Beta-lactam antibiotics

  • It is only effective against dividing organisms
  • Division requires cell wall synthesis - leads to lysis if cell wall is disrupted
  • So, penicillins are BACTERICIDAL (lysis of bacteria)
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12
Q

Give some examples of penicillin antibiotics

A
  • Amoxicillin
  • Benzylpenicillin
  • Flucloxacillin
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13
Q

Give the side effects of penicillin

A

Few side effects

  • Penicillin allergy (hypersensitivity reactions are like skin rashes, hives, itchy eyes, and swollen lips, tongue, or face)
  • Anaphylactic shock is very rare but can be fatal
  • Wide-spectrum antibiotics can cause GI disturbances and candida
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14
Q

Describe resistance to penicillin by some bacteria

A

Some penicillins are inactivated by B-lactamases (enzyme), which are secreted by bacteria, destroying the antibiotic - thus creating resistance
- e.g. Amoxicillin, flucloxacillin

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15
Q

Describe how penicillin resistance (by B-lactamases) are overcome

A

Clavulanic acid is included with some agents (e.g. amoxicillin) to inhibit the B-lactamase enzymes:

Co-amoxiclav = amoxicillin + clavulanic acid

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16
Q

Describe cephalosporins

A

It is a Beta-lactam antibiotic

  • with a similar MOA to penicillins (transpeptidase inhibitor - preventing cross-linking of peptidoglycans in the cell wall)
  • It is widely given parentally
  • About 10% of penicillin-sensitive patients will have an allergic reaction to cephalosporins
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17
Q

Give some examples of cephalosporin antibiotics

A
  • Cefaclor
  • Cefalexin
  • Cefotaxime
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18
Q

Describe the mechanism of action of glycopeptide antibiotics

A

They inhibit peptidoglycan biosynthesis:

  • by binding to D-Ala-A at the terminal of the growing peptide chain during cell wall synthesis
  • resulting in the inhibition of transpeptidase
  • further preventing elongation + cross-linking of the peptidoglycan chains (transpeptidation)
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19
Q

Give some examples of glycopeptide antibiotics

A
  • Vancomycin

- Teicoplanin

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20
Q

Describe the use of vancomycin

and give its side effects

A

Vancomycin is bactericidal

  • and given by I.V. for multi-resistant Staphylococcus aureus (MRSA) infections
  • and given orally for pseudomembranous colitis

Side effects:

  • ototoxicity
  • nephrotoxicity
21
Q

List the different types of protein synthesis + nucleic inhibitors and metabolic pathway inhibitors

A

Antibiotics inhibiting protein synthesis:

  • Tetracyclines
  • Macrolides
  • Aminoglycosides

Antibiotics inhibiting Bacterial DNA:

  • Quinolones
  • Sulphonamides
  • Trimethoprim
22
Q

Describe tetracyclines, and give it’s MOA

A

It is an antibiotic that inhibits protein synthesis:
MOA: tetracyclines inhibit protein synthesis, by binding to the 30s subunit of the bacterial ribosome and preventing tRNA from binding at the acceptor site (A)

Tetracyclines:

  • actively accumulate in bacterial cells
  • are BACTERIOSTATIC
  • are resistant to a wide range of bacteria - but doxycycline used in exacerbations of acne and bronchitis
23
Q

Give some examples of tetracyclines

A
  • Tetracyclines
  • Oxytetracyclines
  • Doxycycline
24
Q

Give some side effects of tetracyclines

A
  • Bone staining (avoid giving to under 12s)

- Phototoxicity

25
Q

Describe macrolides, and give it’s MOA

A

Antibiotic, that can be bacteriostatic or bactericidal
- They have a similar antibiotic spectrum as penicillins - a good alternative if px has a penicillin allergy

MOA:
- Macrolides prevent the translocation of the 50s subunit of the bacterial ribosome along the mRNA and hence inhibit protein synthesis

26
Q

Give some examples of macrolide antibiotics

A
  • Azithromycin
  • Clarithromycin
  • Erythromycin
27
Q

Give some side effects of macrolides

A

Macrolides are cytochrome P450 inhibitors and associated with a range of drug interactions
(increasing conc. of interacting drugs) - theophylline, warfarin

Side effects:

  • Nausea (especially erythromycin)
  • Cardiac - QT prolongation
28
Q

Describe aminoglycosides, and give it’s MOA

A

They are bactericidal antibiotics - used to manage infections caused by gram -ve bacteria
- They have a synergy with penicillin - breakdown of the cell wall, leads to increased uptake of aminoglycosides

MOA:
- Aminoglycosides bind irreversibly to the 30s subunit of bacterial ribosomes, hence leading to the misreading of mRNA, and interferes with protein synthesis

29
Q

Give some examples of aminoglycoside antibiotics

A
  • Gentamicin
  • Amikacin
  • Neomycin
  • Tobramycin
30
Q

Give the uses of gentamicin

A

Gentamicin is an aminoglycoside antibiotic

  • that is most widely used against gram -ve bacteria alongside penicillins
  • It is used in sepsis, infective endocarditis, and pseudomonas aerunginosa infections
  • Give via injections

Caution!

  • Half-life is 2-3 hours
  • IT IS A DRUG OF NARROW TW: drug monitoring needed
  • Mainly excreted unchanged in urine - CAUTION in patients with lower renal function
31
Q

State some side effects of aminoglycosides (gentamicin)

A
  • Ototoxicity

- Nephrotoxicity

32
Q

List some types of antibiotics that inhibit bacterial DNA

A
  • Quinolones
  • Sulphonamides
  • Trimethoprim

(metronidazole)

33
Q

Describe quinolones

A

Antibiotics that are inhibitors of bacterial DNA gyrase and topoisomerase IV
- Quinolones are bactericidal

34
Q

Give the mechanism of action of quinolones

A

In gram +ve:
- DNA gyrase is inhibited, hence supercoiling of bacterial DNA is inhibited (supercoiling is essential for DNA repair + replication)

In gram -ve:
- Topoisomerase IV is inhibited, which interferes with the separation of DNA strands on replication

35
Q

Give some examples of quinolone antibiotics

A
  • Ciprofloxacin

- Norfloxacin

36
Q

Give some side effects of quinolones

A
  • Disabling, long-lasting, potentially irreversibly adverse reactions affecting musculocutaneous + nervous systems have been reported very rarely seen with fluoroquinolone abx

Fluoroquinolone treatment should be discontinued at 1st signs of serious adverse reaction:
- tendon pain or inflammation

  • there is also an increased risk of tendon rupture/convulsions with steroids and NSAIDs
  • inhibition of P450 enzymes
37
Q

Describe metronidazole

A

It is a pro-drug (inactive); it needs to be activated to exert antibacterial/antiprotozoal actions

it has interaction with alcohol

38
Q

Give the mechanism of action of metronidazole

A

It is activated by anaerobic bacteria to cytotoxic products, which damages the helical structures of DNA - fragmentation of DNA, protein, and the cell membrane

39
Q

Give clinical uses of metronidazole

A
  • It is used against anaerobic bacteria and protozoa

- Also used for surgical prophylaxis (high-risk procedure)

40
Q

Describe sulphonamides

A

Bacteriostatic antibiotics, which work to inhibit the production of folate (DNA synthesis)
- there is a high degree of bacterial resistance to sulphonamides

41
Q

Give the principle upon which sulphonamides work as an antibiotic agent,

hence give the MOA of sulphonamides

A

To make DNA, folate is needed
- Bacteria make folate, by converting p-aminobenzoic acid (PABA) into folate using the enzyme dihydropteroate synthetase

MOA:

  • Sulphonamides inhibit the growth of bacteria by competitively inhibiting the enzyme dihydropteroate synthetase, involved in the synthesis of folate from PABA
  • The availability of DNA and RNA precursors is therefore reduced

In effect, sulphonamide is a PABA antagonist

42
Q

Give an example of a sulphonamide antibiotic

A

Sulfasalazine (sulfapyridine-aminosalicylate)

  • which is widely used in inflammatory bowel disease
  • and rheumatoid arthritis and sulfamethoxazole
43
Q

Give some side effects of sulphonamides

A
  • Skin rash, nausea, headache, and very rarely Stevens-Johnson syndrome
  • Use silver sulfadiazine for infected burns
44
Q

Describe trimethoprim

A

So, trimethoprim is a folate antagonist

  • trimethoprim is less potent against the human form of the enzyme (DHFR, which trimethoprim inhibits)
  • It is bacteriostatic
  • Bacteria have a high degree of resistance to them
  • They have a narrow antibiotic spectrum

Uses:
- Main use is to treat simple urinary tract infections like cystitis

45
Q

Give the MOA of trimethoprim

A

In the pathway to make RNA, folate is converted to tetrahydrofolate.

Trimethoprim is a folate antagonist:
- It inhibits the bacterial enzyme dihydrofolate reductase, which converts folate to tetrahydrofolate

46
Q

Give the side effects of trimethoprim

A

Side effects:

- Limited, but make sure to avoid first 3 months of pregnancy (folate is important)

47
Q

Explain what co-trimoxazole is, and give its uses

A

Co-trimoxzole is a combination of antibiotics:
- Co-trimoxozole = trimethoprim + sulfamethoxazole

Uses:
- limited uses in treatment, except for pneumonia causes by yeast-like fungus pneumocystis jiroveci in immunocompromised patients (AIDS or transplant px)

48
Q

Give the principles upon which selection of antibiotics is based:

A
  • Guided by Culture and Sensitivity testing
  • Be aware of patterns of resistance
  • Query about allergies!
  • Apply pharmacological knowledge:
    > IV for rapid effects
    > Oral route: depends on bioavailability (f)
  • Be aware of drug-drug interactions
  • Patient education; considering MDT approaches
  • Advise the patient to COMPLETE THE COURSE
    > there could be small pool of bacteria remaining

Medicine 2 - 03 Pneumonia (8 decks)

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