Drugs interfering with protein synthesis

Question 1

Bacterial protein synthesis.

Answer 1

1. DNA
2. DNA transcribed into mRNA.
3. mRNA interacts with ribosome complex to produce a protein

Question 2

1. What is different about bacteria ribosome complex that allows us to selectively target the protein synthesis of bacteria rather than the protein synthesis of mammalian cells?

Answer 2

1. Ribosome complex is different. It is a 70s (50s and 30s subunit) ribosome (relating to the charge and size and shape). 50s made up of 34 proteins and lots of ribosomal RNA.
   Eukaryotic ribosomes are 80s and made up of a different number and type of proteins and different ribosomal RNAs. This is a way of selectively targeting bacterial cells – selective binding.

Question 3

Drugs that inhibit protein synthesis.

Answer 3

Aminoglycosides
Macrolides
Tetracyclines
Chloramphenicol

Question 4

How do aminoglycosides affect in terms of protein synthesis?

Answer 4

They produce misreading in translation so the wrong tRNA binds to the ribosome and incorrect amino acid added to the chain or early termination occurs, overall causing the wrong protein being produced and therefore being dysfunctional.

Question 5

1. What bacteria type are aminoglycosides generally effective against?
2. How do aminoglycosides gain access to the bacterial cell?

Answer 5

1. Gram -ve. e.g. E. coli but some have broader spectrum of activity.
2. They must be transported into the bacterial cell across the outer membrane, partly down concentration gradient, partly using energy in a transport process – more efficient if the energy produced is derived from aerobic respiration.

Question 6

1. Aminoglycosides bactericidal or bacteriostatic?
2. Aminoglycosides concentration-dept or time-dept?
3. Aminoglycosides absorption? – so what administration is best?
4. Aminoglycosides excretion?
5. Aminoglycosides adverse reactions?

Answer 6

1. Generally bactericidal.
2. Conc-dept.
3. Poor gut absorption. – IV, SC, intramammary injections, topical (eye/ear drops).
4. Renal excretion.
5. Nephrotoxicity (reversible), ototoxicity (effect on hearing and balance – not reversible – there are predispositions)

Question 7

How is nephrotoxicity caused by aminoglycosides?

Answer 7

• The drugs bind to the proximal tubule cells.
• Drugs get taken up into the cells.
• Accumulate into the intracellular compartments and cause changes in cell structure and function.
• Also reduce the glomerular filtration rate.

Question 8

Action of macrolides in terms of protein synthesis?

Answer 8

• Bind to the ‘P’ site and prevent translocation – ribosome cannot move along mRNA so cannot produce protein.
• May also inhibit transpeptidation, cause premature release of ribosome complex

Question 9

1. Macrolides bactericidal or bacteriostatic?
2. What type of bacteria are macrolides effective against?
3. Distribution around the body of macrolides?
4. Good administration route?
5. Adverse reactions to macrolides?

Answer 9

1. Bacteriostatic (erythromycin is bactericidal at high doses).
2. Gram +ve aerobic bacteria.
3. Wide distribution around the body.
4. Very good orally.
5. GI upset – interfering with normal bacterial constituents of the guts, can cause D+.

Question 10

How do tetracyclines affect bacteria in terms of protein synthesis?

Answer 10

• Bind to the A site – Stop/block tRNA from binding to the ribosome complex – No protein produced as stopping tRNA bringing the next amino acid.
• May have the effect of prematurely ending a protein being made.

Question 11

1. Why are tetracyclines not used much anymore?
2. Spectrum of activity?
3. Administration route of tetracyclines?
4. Distribution of tetracyclines?
5. Bacteriostatic or bactericidal?

Answer 11

1. A lot of resistance.
2. Wide spectrum – Effective against gram +ve and gram -ve bacteria and aerobic and anaerobic bacteria.
3. Oral availability varies by drug. Absorption is impaired by calcium and milk products (inhibits uptake).
4. Widely distributed around the body including CNS.
5. Bacteriostatic.

Question 12

1. How do the tetracyclines gain access to the bacterial cell?
2. Do tetracyclines affect mammalian protein synthesis?

Answer 12

1. Access into the cell is partly by diffusion, partly by a carrier protein.
2. Yes, they do inhibit mammalian protein synthesis but mammalian cells do not efficiently transport tetracyclines across the cell membrane.

Question 13

What mechanism causes such a high resistance of bacteria to the tetracyclines?

Answer 13

The tetracyclines can be pumped out of bacterial cells by efflux pump so bacteria with this ability will never allow tetracyclines to reach a high enough concentration to cause any effect on them.

Question 14

Adverse reactions to tetracyclines?

Answer 14

Common
GI disturbances – Superinfection by fungi, yeasts and resistant bacteria possible.
– Particularly ruminants so should not be administered orally to ruminants – can be lethal.
Oral doxycycline can cause oesophageal ulceration in cats, so should be given followed by syringe of water.
– IV administration can cause hypotension and collapse.
– Damage to teeth and bones (calcium containing) – bind to calcium – protective layer compromised, hypersensitivity, increased wear and fracture risk.
– Can slow bone development and inhibit bone repair.

Question 15

1. How do chloramphenicol drugs affect bacterial protein synthesis?
2. Which chloramphenicol drug can be given to food-producing animals?
3. Adverse reactions of chloramphenicol?
4. Spectrum of activity of chloramphenicol drugs?
5. Good administration route?
6. Bactericidal or bacteriostatic?

Answer 15

1. Inhibit peptide bond formation between amino acids so proteins are not produced.
2. florfenicol.
3. Can cause anaemia by suppression of bone marrow (production of new blood cells), can interfere with antibody formation, metabolism poor in cats.
4. Wide spectrum of activity.
5. Well absorbed at oral dosing.
6. Bacteriostatic.