PHARMACOLOGY - Antimicrobials Flashcards
What is the mechanism of action of tetracyclines?
Tetracyclines reversibly bind to the 30S subunit of the bacterial ribosome, preventing the binding of tRNA and thus inhibiting protein synthesis
What is the spectrum of action of tetracyclines?
Broad spectrum antibiotic
How should tetracyclines be administered?
Intravenous (I.V)
Intramuscular (I.M)
Why should tetracyclines not be administered orally?
Tetracyclines are chelating agents and would form complexes with the metal ions in food
How are tetracyclines eliminated?
Tetracyclines are renally excreted and excreted in the bile
Which mechanism increases the half life of tetracyclines?
Tetracyclines undergo enterohepatic recirculation (eliminated in the bile but recirculated into the gastrointestinal tract), increasing the half life of the drug
How do tetracyclines cause severe diarrhoea in horses?
Tetracyclines undergo enterohepatic recirculation and can thus wipe out the normal gut microflora in horses, leading to severe diarrhoea
What are the risks of rapid I.V. administration of tetracyclines?
Rapid I.V. administration of tetracyclines can lead to hypotension and sudden collapse as tetracyclines are chelating agents and will form complexes with calcium ions
How can hypotension and sudden collapse be avoided with I.V. administration of tetracyclines?
This effect can be avoided via slow infusion of the drug or pretreatment I.V. calcium
Why should tetracyclines be avoided in young animals?
Tetracyclines are chelating agents and will chelate with active centres of ossification
Name two long-acting tetracyclines
Minocycline
Doxycycline
Why is doxycycline used in patients with renal dysfunction?
Doxycycline is not renally excreted and this can be used in patients with renal dysfunction without risking further damage
What is the mechanism of action of macrolides?
Macrolides reversibly bind to the 50S subunit of bacterial ribosomes, preventing the addition of new amino acids to the polypeptide chain, thus inhibiting protein synthesis
What is spectrum of activity of macrolides?
Active against most Gram positive and some Gram negative bacteria
Why are macrolides often administered orally as salts?
Macrolides are weak bases so would mainly exist in their ionised form due to the acidic environment in the stomach and won’t be able to cross cell membranes to enter the circulation. Through administering these drugs in the form of salts, this improves the stability of these drugs
Why should I.M. administration of macrolides be avoided?
I.M. administration of macrolides can lead to injection site reactions and hypersensitivity
What allows macrolides to be easily distributed to sites of inflammation?
Macrolides can enter phagocytic cells, increasing their distribution to inflammatory sites
What is the main risk of macrolide use in horses?
Serious or even fatal macrolide-induced gastrointestinal disturbances
Give an example of a macrolide drug
Erythromycin
Why are aminoglycosides and fluoroquinolones used sparingly in veterinary medicine?
Aminoglycosides and fluoroquinolones are used sparingly as only one mutation is required for bacteria to develop antibiotic resistance to these drugs
What is the mechanism of action for aminoglycosides?
Aminoglycosides bind to the A site of the 16S subunit of the 30S subunit of the bacterial ribosome, resulting in mistranslation resulting in errors in protein synthesis
What is the spectrum of activity for aminoglycosides?
Narrow spectrum antibiotics
Why are aminoglycosides narrow spectrum antibiotics?
Aminoglycosides require oxygen-dependent polyamine carriers to enter bacterial cells and thus can only target aerobic bacteria
Why do aminoglycosides have such poor distribution?
Aminoglycosides have low lipid solubility
