Antibiotics Flashcards
What is the mode of action of penicillins?
Inhibit cell wall synthesis by preventing cross-linking of peptidoglycan
Are penicillins bactericidal?
Yes
What are the side effects of penicillins?
Very few
What is the spectrum of penicillins?
Narrow to broad spectrum
How are penicillins excreted?
Via the kidneys
Are penicillins safe in pregnancy?
Yes
What are the five types of penicillins?
- penicillin
- flucloaxacillin
- amoxicillin
- Peperacillin/tazobactam
- co-amoxiclav
What is flucloxacillin used to treat?
Only staphylococci and streptococci infections
How is amoxicillin absorbed?
What destroys amoxicillin?
Best absorbed orally
B-lactamase
What is the spectruum of Piperacillin/Tazobactam?
Broad spectrum
Will treat mostly anything even pseudomonas
How is piperacillin/tazobactam administered?
IV
What is Co-amoxiclav a mixture of?
Amoxicillin
Clavulanic acid (B-lactamase inhibitor)
What is the method of action for cephalosporins?
Inhibits cell wall synthesis by preventing cross-linking of peptidoglycan
Are cephalosporins bactericidal?
Yes
What are the unwanted actions of cephalosporins?
Kill off normal gut bacteria & allow overgrowth of C.diff causing nasty gastroenteritis
What spectrum to cephalosporins work across?
Broad spectrum, each generation is becoming progressively broader spectrum
How are cephalosporins excreted?
Via the kidneys
Are cephalosporins safe in pregnancy?
Yes
How do glycopeptides work?
Cell-wall active antobiotics, binds to the end of the growing peptide chain during synthesis of peptidoglycan & prevents cross-linking: weakening the bacterial cell wall.
Are penicillins bactericidals?
Yes
What is an unwanted effect of vancomycin?
Builds up to toxic levels in patients who have kidney failure, causing further damage.
What spectrum do glycopeptides work across?
Only active against organisms with a gram +ve cell wall
How are glycopeptides excreted?
Via the kidneys
How are glycopeptides administered?
What is the exception?
Have to be given IV
Vancomycin can be given orally in the treatment of C.diff as this way it has effect on the gut lumen.
How do antibiotics that inhibit protein synthesis work?
- Attatch to bacterial ribosomes which are structurally different to mamalian ribosome
Are macrolides bacterocidal?
NO
they are bacterostatic: this means they inhibit bacterial growth but do not kill the bacteria, the bacteria are then killed by white blood cells.
What is the exception to bacteriostatic antibiotics?
The aminoglycoside group, they are bacteriosidal
How are macrolides excreted?
By the liver, through the biliary tree and into the gut
How do macrolides enter bacterial cell walls?
They are lipophillic and can do so easily
What are macrolides useful in treating?
- infections where the bacteria enter the hosts cells
- intracellular organisms (legionella)
- Organisms without a proper cell wall (mycoplasma, chlamydia)
- penicillin sensitive patients
Name some macrolides?
Erythromycin
Clarithromycin
Azithromycin
Name an aminoglycoside?
Gentamicin (IV)
How are aminoglycosides excreted?
Excreted in urine
How do aminoglycosides work?
Binds to ribosomes by inhibiting protein synthesis
BUT they are bactericidal
The must be given IV and very occasionally IM
What are aminoglycosides active against?
Mainly gram negative aerobic organisms such as coliforms and pseudomonas aerginosa
What are aminoglycosides used for?
Used in hospital for treating life threatening gram negative infection
What is the limiting factor with aminoglycosides?
They have a narrow therapeutic index;
there is a narrow margin between giving enough antibiotic to treat and enough to overdose
What is an unwanted side effect of aminoglycosides?
Causes damage to the kidneys and the VIII cranial nerve; resulting in
- renal (kidney failure)
- deafness and disturbance of balance
Name two antibiotics that inhibit protein synsthesis but do not fit into a class
Clindamycin
Chloramphenicol
What is clindamycin used for?
2nd line treatment of staphylococcal and streptococcal infections
Active in true anaerobes
What is Chloramphenicol used for?
Mainly used as a tropical treatment for eye infection
How do tetracyclines work?
They inhibit bacterial protein synthesis by attatching to ribosomes and are bacteriostatic
How are tetracyclines excreted?
Via the biliary system: gut
What is doxycyline used for?
Tetracycline used in Tayside
For infections with no proper cell wall
For penicillin allergic patients
Name three antibiotics that work on DNA?
Metronidazole
Trimethoprim
Fluoroquinolone
How does metronidazole work?
It acts by causing strand breakage of bacterial DNA.
What is metronidazole used for?
Infection caused by true anaerobes (bacteria that will only grow when there is no oxygen present in the atmosphere)
i.e. C.diff
Some infections caused by protozoa (organisms that are single-celled parasites)
How can trimethoprum be given?
Can be given on its own orally
OR
Can be given in combination with sulphamethoxazole= co-trimoxazole
What is trimethoprum active against?
Some gram +ve and some gram -ve organisms
How is trimethoprum excreted?
In the urine
Is trimethoprum safe in pregnancy?
From 4th month onward.
How do fluoroquinolones work?
Interacting with topoisomerases (enzymes responsible for the coiling of DNA): bacteria can no longer replicate.
Are fluoroquinolones bactericidal?
Yes
Why is the use of fluoroquinolones restricted?
As they are broad spectrum and may increase the risk of c.difficile infection
What is the unique factor regarding fluoroquinolones?
They are the only oral antibiotic for pseudomonas
What are the two main quinolones and what are they used for?
- Ciprofloxacin (IV, oral)
- complicated UTI infection
- Levefloxacin (IV only)
- Severe CAP in penicillin allegic patients
How do bacteria acquire resistance?
- Genetic Mutation
- misreading of DNA
- Transfer of DNA that codes for antibiotic resistance from one bacterium to another by
- transformation
- conjugation
- Transduction
What is transformation?
When bacteria die and cells break apart, ‘free-floating DNA’ released into the surrounding environment may be ‘scaveneged’ by other bacteria and incorporated into their DNA.
This DNA may contain genes that code for antibiotic resistance and benefit the cell.
What is conjugation?
Bacteria often carry DNA in plasmids
Some plasmids may carry genes that confer resistance to antibiotics
When two bacteria are in close proximity to each other a hollow bridge like structure, known as a pilus forms between the two cells
The plasmid replicates and one copy is transferred via the pilus to the other bacterium
This enables a previously susceptible bacterium to acquire the antibiotic resistance
What is transduction?
Bacterial DNA is transferred from one bacterium to another inside a virus that infects bacteria. These viruses are called bacteriophages or phages
When a phage infects a bacterium it takes over the bacterias genetic process to produce more phage
During this process, bacterial DNA which may code for antibiotic resistance may be accidentaly incorporated into the phages DNA
When the host cell dies and the phages are released from the dead cell, they will then contain DNA from the host bacterium that can be transferred to other bacterial cells
What are the three mechanisms of antibiotic resistance?
Altered antibiotic target binding site
Destruction or inactivation of the antibiotic
Increased efflux
