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Inhibitors of cell wall synthesis Flashcards

1
Q

What are the different classes of inhibitors?

A

β-Lactams, Peptides, Fosfomycin, Bacitracin

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2
Q

Why do cell wall synthesis inhibitors work?

A

Mammalian cells have no cell wall (selective toxicity) and all bacterial cells have a cell wall (gram positive or gram negative)

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3
Q

What is the difference between gram positive and gram negative bacteria?

A

Gram positive has a thick cell wall and gram negative has a thin cell wall

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4
Q

What is the MOA of penicilin?

A

The transpeptidase enzyme in the bacterium is inhibited to disrupt peptidoglycan synthesis. This causes cell wall defects and the ultimate swelling and rupturing of the bacterium

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5
Q

What causes bacterial resistance?

A
  1. Absence of a cell wall
  2. Metabolically inactive bacteria
  3. Altered penicillin binding proteins (pneumococci),
  4. Permeability barrier (e.g. Gram neg. bacteria (E.
    coli) penicillin G cannot penetrate but ampicillin
    can
  5. Some bacteria lack autolysins
  6. Mutations can also reduce or eliminate activity
  7. β-lactamase production (penicillinase) →
    hydrolysis of β-lactam ring → inactivation
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6
Q

What are the natural penicillins?

A
  • Penicillin G (Benzylpenicillin)
  • Penicillin V (Phenoxymethylpenicillin)
    (Both have narrow spectrum and are β-
    Lactamase sensitive)
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7
Q

What are the clinical uses for penicillin G (Benzylpenicillin)?

A
  • Gram pos. cocci and anaerobes:
    – Tonsillitis - Streptococcus pyogenes
    – Pneumonia – Pneumococci
  • Gram neg. cocci:
    – Meningitis - Neisseria meningitides
  • Gram neg. diplococci:
    – Gonorrhea - Neisseria gonorrhoeae
  • Gram pos. rod bacteria:
    – Tetanus, gangrene – Clostridium
  • Gram neg. rod bacteria:
    – Oropharyngial infections - Bacteroides fragilis
  • Spiral-shaped bacteria:
    – Syphilis – Treponema
  • Gram positive facultative anaerobes:
    – Abscesses - Actinomyces
  • Enterococci less susceptible (add aminoglycoside)
  • Prophylaxis:
    – Streptococcal infections
    – Prevention of rheumatic fever recurrence
    – Surgical or dental procedures on patients with
    valvular heart disorders
  • Penicillin G: initial therapy for serious infections
    (infective endocarditis), syphilis (depot prep.
    benzathine penicillin G)
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8
Q

What are the clinical uses for penicillin V (Phenoxymethylpenicillin)?

A
  • 2 – 4 times less active than penicillin G
  • Used mostly for the treatment of less serious
    infections (streptococcal tonsillitis/pharyngitis)
    Or
  • it is used as follow-up antibiotic treatment after
    serious infections responded well to parenteral
    treatment
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9
Q

What drugs are β-Lactamase resistant
penicillins?

A

– Methicillin, nafcillin, oxacillin, dicloxacillin (Not
available in SA)
– Cloxacillin
– Flucloxacillin

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10
Q

What are the uses of β-Lactamase resistant
penicillins?

A
  • Slightly less active than penicillin G
  • They are used for the treatment of mild -
    lactamase positive staphylococcal infections
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11
Q

What are the two β-lactamase sensitive, broad spectrum penicillians (aminopenicillans)?

A

– Amoxicillin (amoxycillin)
– Ampicillin

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12
Q

What are the two extended spectrum aminopenicillans?

A
  • β-lactamase resistant
    – amoxicillin + clavulanic acid (co-amoxiclav)
  • Extend the spectrum
    – ampicillin + cloxacillin in combination
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13
Q

What is the β-lactamase inhibitor?

A

Clavulanic Acid. It is produced by Streptomyces-moulds

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14
Q

What is the MOA of Clavulanic Acid?

A

Clavulanic acid binds covalently near or in the active site of the β-lactamase enzyme
- Most Gram neg. organisms are irreversibly inhibited by clavulanic acid

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15
Q

What are the clinical uses for Ampicillin?

A

Mostly Gram pos bacteria + H. influenza

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16
Q

What are the clinical uses for Amoxicillin?

A

– Gram pos. spectrum similar to penicillin G, ↑
activity against enterococci and Listeria
– Gram neg. spectrum: H. influenzae, E. coli,
Proteus mirabilis, Salmonella & Shigella
* Amino side-chain is hydrophilic → penetration via porins in outer membrane of Gram neg. bacteria is easier
– Drug of choice for: otitis media, sinusitis lower RTI
– Soft tissue infections
– Cholecystitis, GIT infections (incl. thyroid)
– Urinary tract infections (possibility of resistance
developing)
– Prophylaxis to prevent infective endocarditis

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17
Q

What drugs are used as Antipseudomonal penicillins?

A

Piperacillin + tazobactam (β-lactamase inhibitor)

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18
Q

What bacteria are antipseudomonal penicillans most effective against?

A

Pseudomonas aeruginosa

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19
Q

What can be done to prolong the action of Penicillan G?

A
  1. Higher doses above the MIC
  2. Combine with probenecid (a uricosuric drug) (the excretion of penicillin takes place in the acid secretory system in the proximal convoluted tubule of the kidney, prebenecid (an acid) competes with this route and delays the excretion of penicillan)
  3. Depot formulation via intramuscular injection
    * Anionic form (COO-) forms weak water-soluble
    salts with compounds that contain positively
    charged amino groups (procaine)
    – Release of penicillin G from this depot
    formulation → a longer time period
    * Inflammation → ↑ Penetration into CSF and
    synovial fluid
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20
Q

What are the limitations of penicillin G?

A
  1. Narrow spectrum antibiotic
  2. Acid labile
  3. β-lactamase sensitive
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21
Q

What are the side effects of penicillin G?

A
  1. Antibodies formed → hypersensitivity reactions
    (skin rashes → anaphylactic shock) → 5 – 10%
    occurrence
  2. Cross-hypersensitivity between all penicillins
  3. Very high concentrations → administered rapidly via IV or intrathecal injections → neurotoxic effects e.g. convulsions
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22
Q

What are the side effects of β-Lactamase resistant antibiotics?

A
  1. As for penicillin G
  2. Cloxacillin not many side effects, well tolerated
  3. Mild GIT disturbances & hypersensitivity effects
  4. Neutropenia & agranulocytosis described
  5. Flucloxacillin → cholestatic hepatitis
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23
Q

What are the side effects of Extended-spectrum β-lactam antibiotics?

A
  1. Superinfections are possible especially by Candida and Clostridium difficile (Antibiotic associated colitis – especially ampicillin)
  2. Rashes (toxin) rather than allergic reaction
  3. Reduce efficacy of combined oral contraceptive
  4. GIT effects
  5. Infectious mononucleosis (amoxicillin)
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24
Q

What effect does Ampicillin have on the GIT?

A

Weak oral absorption ampicillin → more destruction of the microflora in the gastrointestinal tract (causes diarrhea)

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25
What are the side effects of Co-amoxiclav (Augmentin®)?
* Gastrointestinal discomfort, diarrhea, nausea and vomiting → high dosages * Hepatitis and cholestatic jaundice → clavulanic acid * Amoxicillin and clavulanic acid must also be used with caution during lactation → excreted in mothers milk
26
What are the side effects of Piperacillin?
1. Same as penicillin G 2. Potential → bleeding diathesis
27
What caution must be taken with aminoglycosides and penicillins?
Do not combine probenicid in same infusion, syringe or IV line
28
What are the drug interactions of extended spectrum penicillins?
– Allopuranol (skin rash) – Combined oral contraceptive pill
29
What general cautions are associated with penicillins?
1. Elderly 2. Neonates (extended dose intervals) 3. C/I when allergic 4. Flucloxacillin - porphyria
30
What are Cephalosporins?
Broad-spectrum semi-synthetic antibiotics Contain a β-lactam ring → cross-hypersensitivity reactions may occur with penicillins
31
What is an advantage of Cephalosporins over penicillins?
Inherent greater stability against -lactamases as compared to the penicillins
32
What bacteria are resistant to all cephalosporins?
Enterococci are resistant to all cephalosporins
33
What drugs are in the 1st generation of Cephalosporins and what are their uses?
* 1 st generation: Cefalexin, Cefazolin, Cefadroxil Uses: Streptococci, Staphylococci
34
What drugs are in the 2nd generation of Cephalosporins and what are their uses?
2nd generation: Cefuroxime, Cefprozil, Cefamandole, Cefoxitin Uses: Streptococci, Staphylococci, E. coli, Klebsiella, Proteus, H. influenzae, Enterobacter
35
What drugs are in the 3rd generation of Cephalosporins and what are their uses?
3rd generation: Cefotaxime, Ceftriaxone, Cefixime, Ceftazidime, Cefpodoxime Uses: Gram pos. + H. influenzae, N. gonorrhoeae, Salmonella spp, some active against P. aeruginosa
36
What drugs are in the 4th generation of Cephalosporins and what are their uses?
4th generation: Cefepime, Cefpirome Uses: As for 3rd generation (Gram pos. + Gram neg.) especially P. aeruginosa
37
What drugs are in the 5th generation of Cephalosporins and what are their uses?
5th generation: Ceftaroline Uses: MRSA+MR S. Epidermidis + Gram Neg organisms
38
What causes bacterial resistance to cephalosporins?
1. Bacteria become impermeable to drug 2. Alterations in PBS 3. Autolysins cannot be activated 4. β-Lactamase (cephalosporinases) sensitive
39
How is Ceftriaxone eliminated?
40% hepatic elimination
40
How are cephalosporins excreted?
Excreted mainly via glomerular filtration and tubular secretion (can use probenecid to increase t1/2 except ceftriaxone)
41
How is Ceftaroline fosamil metabolised?
metabolised by plasma phosphatases
42
What is the general rule for 1st generation cephalosporins?
First generation is most effective against Gram pos. organisms
43
What is the general rule for 4th generation cephalosporins?
Fourth generation is similar to 1st generation & effective against Gram neg. Organisms
44
What is the general rule for 5th generation cephalosporins?
Fifth generation active against MRSA and MR S. Epidermidis + Gram neg. Organisms
45
What are the side effects of cephalosporins?
1. Hypersensitivity reactions e.g. – anaphylactic shock, fever, skin rashes, nephritis, granulocytopenia and hemolytic anemia 2. Chemical structure differs enough from penicillins → some people can tolerate them 3. The occurrence of cross-hypersensitivity → 2% 4. Some can also cause alcohol intolerance (cefamandole) 5. Effectiveness of oral contraception ↓ 6. Nephrotoxicity, especially when administered with aminoglycosides or vancomycin 7. Phlebitis can occur (IV) 8. Neurotoxicity at high doses or renal impairment
46
What are the drug interaction of cephalosporins?
1. Alcohol (cefamandole) 2. Warfarin 3. NSAIDs 4. Combined oral contraceptive pills 5. Probenecid 6. Cephalosporins & aminoglycosides in same container may chemically inactivate each other 7. Ceftriaxone – Not to be administered at same time as Ca2+- containing solutions (>48 h)
47
What are the cautions associated with cephalosporins?
Anaphylactic shock (penicillins) Allergy Ceftiaxone CI in hyperbilirubinaemic neonates (prematures)
48
What drugs are Carbapenems?
Imipenem + cilastatin, Meropenem, Ertapenem
49
What is the spectrum of Ertapenem?
narrower spectrum, single daily dosing, IV & IM
50
What is the MOA of carbapenems?
Bactericidal, same as penicillins
51
What is the spectrum of carbapenems?
Very broad spectrum (Gram pos., Gram neg. & anaerobic bacteria)
52
What do carbapenems not work against?
Not active against methicillin-resistant staphylococci
53
What are the clinical uses for Imipenem?
Severe nosocomial infections (septicaemia, endocarditis, lower respiratory tract, genitourinary tract, intra-abdominal, bone & joint, skin & soft tissue)
54
What are the clinical uses for Meropenem?
Alternative treatment for bacterial meningitis (good penetration into CSF)
55
How are carbapenems administrated?
Mostly IV
56
How are carbapenems eliminated?
Kidneys
57
What are the side effects of carbapenems?
1. Similar to other β-lactams (hypersensitivity reactions, GIT effects, haematological abnormalities, CNS effects (seizures at high dosages of imipenem)), ↑ liver enzymes, ↑ serum creatinine & blood urea 2. Red discolouration of urine in children (Imipenem) 3. IV: pain, erythema & thrombophlebitis
58
What are the cautions of carbapenems?
1. Allergy 2. CNS disorders/seizures 3. Renal impairment
59
What drug is a monobactum?
Aztreonam
60
What is the MOA of Aztreonam?
Bactericidal, same as penicillins
61
What is the spectrum of aztreonam?
Good activity against aerobic Gram neg. bacteria only (E. coli, P. aeruginosa, Enterobacter, Citrobacter, Proteus mirabilis, H. influenzae)
62
Is aztreonam cross sensitive to other penicillans or cephalosporins?
No. Can use in pts with penicillin allergy
63
How is aztreonam eliminated?
Kidneys, unchanged
64
What are the side effects of aztreonam?
1. Injection site reactions 2. Rash 3. Rarely toxic epidermal necrolysis 4. Gastrointestinal side effects 5. Drug-induced eosinophilia
65
When is vancomycin indicated?
Reserve antibiotic used for the treatment of life threatening infections
66
What is the spectrum of vancomycin?
– Gram pos bacteria only – Use restricted to cloxacillin-resistant staphylococci & penicillin-resistant enterococci – Alternative agent for prophylaxis & treatment of endocarditis (penicillin-allergic patients) – Gastrointestinal tract infections (pseudomembranous colitis) → Clostridium difficile – No cross-resistance with other antibiotics
67
What is the MOA of vancomycin?
Bactericidal * Inhibits cell wall synthesis → attaching to the D- alanine-D-alanine end of a peptidoglycan pentapeptide * Transglycosylation is inhibited → peptidoglycan cross-linkages do not form * Result → weakened bacterial cell wall → lyses of the bacterium
68
How is vancomycin administered?
IV or orally for pseudomembranous collitis
69
What are the side effects of vancomycin?
1. Fever and skin rashes 2. Administered too rapidly → release of histamine → blushing of the neck and face known as “red-man-syndrome” 3. Ototoxic and nephrotoxic (rare) 4. Nephrotoxic in geriatric patients 5. Therapeutic drug monitoring essential (elderly, children, impaired renal function)
70
What are the DI of vancomycin?
Ototoxic and nephrotoxic drugs (e.g. aminoglycosides
71
What are the cautions of vancomycin?
1. Renal Impairment 2. Elderly patients 3. Neonates/young infants 4. Hearing abnormalities 5. Pregnancy
72
What drug is similar to vancomycin? (same MOA, indications)
Teicoplanin
73
What are the side effects of Teicoplanin?
Same as vancomycin, lower incidence of “red man” syndrome, allergy (cross sensitivity with vancomycin)
74
What is the spectrum of fosfomycin?
Broad spectrum
75
What is the MOA of fosfomycin?
* Interferes with formation of N-acetylmuramic acid * Inhibits early stage in bacterial cell wall synthesis * Bactericidal
76
What causes resistance to fosfomycin?
inadequate transport of drug into cell
77
What is the spectrum of fosfomycin?
Gram pos. and neg., synergism with β- lactams, aminoglycosides or quinolones
78
Pharmacokinetics of fosfomycin
– Oral → absorption delayed by food (take 2 hrs before meal) – Plasma half life ~ 4 h – Fosfomycin trometamol → prodrug → levels in urine (30 – 60%) – Excreted in breast milk – Excreted in urine → Therapeutic levels (1-3 days)
79
What are the uses of fosfomycin?
1. Single-dose therapy for acute uncomplicated lower urinary tract infections (sensitive E. Coli) → woman and female children > 5 years 2. Prophylaxis in diagnostic and surgical transurethal procedures in adult men
80
What are the side effects of fosfomycin?
GIT disturbances, skin rashes
81
What are the drug interactions of fosfomycin?
Metoclopramide → ↓ serum & urinary concentrations of fosfomycin (avoid)
82
What are the cautions for fosfomycin?
1.C/I in renal failure 2.Caution → pregnancy & lactation

Pharmacology (11 decks)

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