Antibiotic therapy Flashcards
Tetracyclines
What is the chemical characteristic of tetracycline molecules
They have four (“tetra”) hydrocarbon (“cyclic”) rings
What is the mechanism of action of tetracyclines
They act by inhibition of messenger RNA translation in the cytoplasm by reversibly binding to the 16S part of the small (30S) ribosomal subunit
- This stops the transport of amino acids by transfer RNA to the ribosome
Tetracyclines are a relatively broad-spectrum group of antibiotics, that are effective against certain gram-positive and negative aerobes and anaerobes
They are also effective against Mycoplasma, Bartonella, some Mycobacteria and Chlamydia
They are concentration-dependent, bacteriostatic drugs
What are the pharmacokinetics characteristics of doxycycline
well absorbed after oral administration (not affected by food)
highly lipid soluble (= wide tissue distribution including the eye and the CNS)
It is effective against intracellular pathogen
What is the main precaution when using hydrochloride formulation of tetracyclines
Care must be taken to ensure that oral doses are followed by a water chaser or given directly before food
Retained tablets or capsules have been known to cause esophageal irritation, possibly leading to stricture formation
How is doxycycline eliminated
The major route of elimination of doxycycline is via diffusion through the gastrointestinal wall, after which it is thought to be mostly inactivated by chelate formation within the gut lumen
- therefore, it is not effective against organisms causing LUT infections
How could you explain the anti-inflammatory effect of tetracyclines
It is thought that they inhibit matrix metalloproteinases
What are the possible side effects of doxycycline
Doxycycline is a safe drug even if high doses may cause inappetence and diarrhea
Because it is not excreted by the kidneys, it is safe to use in animals with renal disease
Doxycycline is much less likely than other tetracyclines to cause staining of deciduous teeth of neonates (either administered to the mother in the last few xeeks of pregnancy or to the kitten in the first few months of life)
