20 - Selective Toxicity & Antibiotics Flashcards
The aim of a selectively toxic antibiotic is to destroy a parasite while remaining relatively ________ to the host.
The aim of a selectively toxic antibiotic is to destroy a parasite while remaining relatively non-toxic to the host.
Common targets of selective toxicity include:
-
Infective organisms
- Metazoa
- Protozoa
- Fungi
- Viruses
- Bacteria
-
Own cells
- Tumour cells (chemotherapy)
State 4 ways to improve selectivity…
- Unequal distribution
- Targeting structural differences between cells
- Stereochemistry
- Biochemistry of disease or receptor
The development of antibiotic resistance is exacerbated by _____. There is also a decrease in the _____________________ . One way of reducing the development antibiotic resistance is _____________ (awareness of approapriate use).
The development of antibiotic resistance is exacerbated by misuse. There is also a decrease in the number of new antibiotics reaching market. One way of reducing the development antibiotic resistance is antibiotic guardianship (awareness of approapriate use).
Antibiotics have 3 potential modes of action…
- Bacteriostatic
- Bacteriocidal
- Bacteriolytic
Name 6 common antibiotic targets…
- Cell membrane
- Cell wall
- Protein synthesis (ribosomes)
- RNA polymerase
- DNA synthesis
- Folate metabolism
The five main types of antibiotic are…
- Penicillins
- Sulfanamides
- Fluoroqinolones
- Macrolides
- Tetracyclines
Penicillins are characterised structurally by the presence of a _______________ . Bacteria resistant to penicillins possess the enzyme ___________________.
Penicillins are characterised structurally by the presence of a beta lactam ring. Bacteria resistant to penicillins possess the enzyme beta lactamase.
Name an early penicillin, which was acid labile, thus had to be given intravenously…
Benzylpenicillin
Name 2 broad spectrum penicillins and their advantages…
Ampicillin and amoxicillin
Additional amino group helps penetrate gram negative outer membranes. Better absorption.
In addition to broad spectrum penicillins, name 3 other types…
- Beta lactamase resistant penicillin
- Extended spectrum penicillin
- Reversed spectrum penicillin
Name an adverse reaction to penicillins…
Hypersensitivity (rashes, fever, serum sickness and in rare cases anaphylaxis)
Sulfonamide antibiotics target…
Folate synthesis
Anti-metabolite mimicking the structure of PABA, interfering with dihydrofolate reductase (needed for DNA synthesis components)
What gives sulfanamides their selectivity?
Eukaryotic cells don’t need to synthesise their own folate
Sulfanamide pharmacokinetics
a) good oral absorption and wide distribution through CNS
b) poor oral absorption and limited distribution through CNS
c) good oral absorption but limited distribution through CNS
d) poor oral absorption but wide distribution through CNS
Sulfanamide pharmacokinetics
a) good oral absorption and wide distribution through CNS
b) poor oral absorption and limited distribution through CNS
c) good oral absorption but limited distribution through CNS
d) poor oral absorption but wide distribution through CNS
Which type of antibiotics target DNA replication?
Fluoroquinolones
How to fluoroquinolones target DNA replication?
- DNA replication via Type II topoisomerases
- DNA gyrase (gram-)
- DNA topoisomerase IV (gram+)
Name the enzyme target of fluoroquinolones in gram positive bacteria…
DNA topoisomerase IV
Pharmacokinetics of fluoroqinolones…
Well absorbed in ( upper GI / lower GI / nasal passage / sublingually) . Excreted mainly in ( tubular secretion / faeces)
Pharmacokinetics of fluoroqinolones…
Well absorbed in upper GI. Excreted mainly in tubular secretion.
Fluoroqinolones inhibit which CYP?
CYP1A2
Outline adverse reactions to fluoroqinolones…
Hypersensitivity and GIT disturbances
Macrolides are antibiotics that target…
Bacterial ribosome (protein synthesis)
Name the target and describe the effect of macrolide antibiotics…
- Target: 70S prokaryotic ribosome
- Blocks the translocation of peptide, encourages dissociation (some prevent peptide bond formation)
Name 3 adverse reactions associated with macrolides…
- Cholestatic hepatitis
- GIT disturbance
- Transitory auditory impairment
teTetracyclines target…
Bacterial ribosome (protein synthesis)
(Elongation phase- blocks the A site)
Pharmacokinetics of tetracyclines
Better absorbed in a ( fasted / fed ) state.
Widely distributed with a relatively ( short / long ) half life.
Excreted via ______ & _____ .
Pharmacokinetics of tetracyclines
Better absorbed in a fasted state.
Widely distributed with a relatively long (6-18hrs) half life.
Excreted via kidney & bile.
Tetracycline may have an adverse reaction due to interaction with calcium, causing…
Bone and teeth problems in children
