CPTP 3.10 Pharmacology of Antimicrobials 1 Flashcards Preview

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Flashcards in CPTP 3.10 Pharmacology of Antimicrobials 1 Deck (49)
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What does antimicrobial chemotherapy include?

• Synthetic chemicals to destroy pathogens
• Naturally-occuring antibiotics


What is selective toxicity?

When one kind of cell is influenced strongly without any effect on other cells.


What two things must be considered when choosing an antimicrobial agent?

• The patient (pharmacokinetics, allergies, pregnancy, other medications)

• The pathogen (antimicrobial sensitivities)


What are broad spectrum and narrow spectrum antibiotics? What are the main differences between them and their use?

Broad spectrum:
• Target both gram positive and gram negative antibiotics
• More likely to cause resistance due to lack of specificity
• Prescribed if you don't know the identity of the pathogen

Narrow spectrum:
• Targets either gram negative or gram positive bacteria
• Less likely to cause resistance due to increased specificity
• Prescribed if the causative agent is known


What is the main disadvantage of narrow spectrum antibiotics?

• If the causative agent is misidentified, the treatment may be completely ineffective


How are broad and narrow spectrum antibiotics used in practise?

Broad spectrum antibiotic is used until the causative agent is known, then the patient is switched to a narrow spectrum antibiotic


In what ways can antibiotics be classified?

Broad and narrow spectrum

Bacteriostatic & bacteriocidal:
• Bacteriostatic - Inhibits bacteria from reproducing but doesn't kill them
• Bacteriocidal - Actively kills bacteria


How are antibiotics placed into bacteriostatic and bacteriocidal categories?

Categorisation is not distinct, it depends not only on the identity of the antibiotic, but also:
• Bacterial species targeted
• The concentration of the drug used


What are the 'classes' of targets for antimicrobial action in the bacterial cell?

Class I:
• Utilisation of carbon sources (e.g. glucose) to generate ATP
• Synthesis of carbon compounds used in Class II reactions

Class II:
• Utilisation of precursors to create:
> Amino acids
> Phospholipids
> Nucleotides
> Carbohydrates (from Class I precursors)

Class III:
• Assembly of small molecules into macromolecules:
> Proteins
> Polysaccharides


What are the limitations of using Class I targets?

• Bacteria often use similar mechanisms to humans to acquire and internalise sugars
• Bacteria are very good at switching to different substrates

Generally not effective


What is the best type of selective toxicity against bacteria?

Class III targeting - there are distinct differences between the pathogen and the host, therefore the toxicity is selective


What are the three major targets of antibiotics?

• Cell wall
• Nucleic acid synthesis
• Protein synthesis


What antibiotics does beta-lactam form the core structure of?

• Penicillins
• Cephalosporins


Name the penicillins in the formulary and their route of administration

• Amoxicillin
• Flucloxicillin

• Benzylpenicillin


What is the mechanism of action of the penicillins?

• Bacteriocidal
• Binds to penicillin binding proteins on susceptible microorganisms
• This inhibits peptide cross-linking within the cell wall


Describe the pharmacokinetics of penicillins, with regard to distribution and excretion.

• Diffuse into all tissues but not CSF
• 60% is plasma protein bound

• Excreted in the urine


In what case might a penicillin cross the blood brain barrier into the CSF?

If the meninges are inflamed


What can penicillins become metabolised into?

Penicilloic acid


In what population in clearance of penicillins reduced?



Penicillin prevents peptide cross-linking between which proteins in the cell wall?

• N-acetyl glucosamine (NAG)
• N-acetyl muramic acid (NAM)


What are the penicillin binding proteins? What do they do?

Transpeptidase enzymes

These form the cross links between NAG and NAM using 4 amino acids


What are the components of penicillins? What does the active component do do?

(IMG 4)
• A carboxylic acid side chain

• An acylamino side chain

• Thiozidine ring

• Beta-lactam ring
>Forms a covalent bond with transpeptidase enzymes (penicillin binding protein)
>This blocks the active site and prevents the cross linking


What is the R (variable) group between the different penicillins?

The acylamino side chain


What are the adverse drug reactions of penicillins?

• GI disturbances
• Hypersensitivity and anaphylaxis


What causes GI disturbances when penicillins are given?

Altered gut flora

(D&V, nausea)


What are the components of cephalosporins?

(IMG 5)
• Dihydrothiazine ring
• Beta-lactam ring (works in the same way as penicillins)


What is the benefit of the dihydrothiazine ring on cephalosporins?

Makes the beta-lactam more resistant to beta-lactamases


What happens when antibiotics successfully prevent cross links to form in the cell wall?

The bacteria cell explodes out through the weakened cell wall, killing it


What type of antibiotics are cephalosporins?

• Broad spectrum
• Bacteriocidal


Name the formulary cephalosporins and their route of administration.

Cefalexin - oral
Cefotaxime - parenteral