Antibiotics Flashcards
Define bacericidal?
Kills bacteria
Define bacteriostatic?
Inhibits bacterial growth
What is a narrow spectrum antibiotic?
Acts on a limited range of bacteria
What is a broard spectrum antibiotic?
Acts on a wide range of gram positive and gram negative organisms
What are the 3 main ways antibiotics work?
1) Acting on bacterial cell walls. (eukaryotes don’t have a cell wall)
2) Affecting the bacterial ribosome (eukaryotes have 80S ribosomes, prokaryotes have 70S)
3) Acting directly on bacterial DNA (bacterial DNA is different from mamalian DNA
Which antibiotics act on the cell wall?
Penicillins, cephalosporins and glycopeptides
How do penicilins work?
Inhibit cell wall synthesis- bacteriocidal
1) PG subunits are produced inside the cell and transported across the cell membrane and cross linked with each other for stability
2) Penicillin prevents the cross linking of PG subunits
3) Penicillin also stimulates the production of autolysins which break down the cell wall
=> more difficult to withstand high osmotic pressure
=> Bacterial wall ruptures and bacteria die
How do cephalosporins work?
Same as penicillins
What are the adantages and disadvantages of penicilins?
+ safe and few side effects
+ Range from narrow to broad spectrum
+ Excreted rapidly via kidneys
+ safe in pregnancy
- some patients are allergic to penicillin
- Rapid excretion means frequent dosing of 4-6 times daily
Are penacilins safe in pregnancy?
Yes
There are 2 broad types of penicilin, which must be given IV?
Benzylpenicilin as it is destroyed by stomach acid
NB: can be given IM for a long lasting effect
There are 2 broad types of penicilin, which is given orally?
Phenoxymethyl penicillin
What is the drug of choice for a staph aureus infection?
Flucloxacillin IV or PO
Give 4 examples of penicillin based antibiotics?
Flucloxacillin
Amoxacilin
Co-Amoxiclav
Piperacillin/Tazobactam
Characteristics of flucloxacillin?
Narrow spectrum
Used for Staph and strep infections
Commonly used for skin and soft tissue infections
IV or PO
Characteristics of Amoxicillin?
Broard spectrum
Not effective against organisms which produce beta lactamase
Well absorbed through PO
IV or PO
Characteristics of Co-Amoxiclav?
Combination of amoxicillin and clavulanic acid (beta lactamase inhibitor)
Broad spectrum
Can lead to C diff infection
IV or PO
What is clavulanic acid?
A beta lactamase inhibator with no antibiotic properties of its own
Characteristics of Piperacilin/tazobactam?
Combination of piperacillin (antibiotic) and tazobactam (beta lactamase inhibator)
Broard spectrum
Treats everything except MRSA and some ESBL (extended spectrum beta lactamse) producing organisms
IV ONLY
What are the advantages and disadvantages of cephalosporins?
\+ Excreted via kidneys \+ Few side effects \+ Safe in pregnancy \+ Broad spectrum - Kill off normal gut flora and allow overgrowth of C difficile causing gasteroenteritis
Are cephalosporins safe in pregnancy?
Yes
What are the 1st generation (least broad spectrum) cephalosporins and what are they commonly used for?
Cefalexin PO for a UTI
What are the 2nd generation cephalosporins and what are they commonly used for?
Cefuroxime IV or PO (not really used)
What are the 3rd generation (most broad spectrum) cephalosporins and what are they commonly used for?
Cefixme PO for gonorrhea
Cetriaxone IV for meningitis
Ceftazimide IV for Pseudomonas
Why are cephalosporins avioded?
The help spread C difficile in hospitals
How do glycopeptides work?
1) Binds to the end of growing pentapeptide chain during PG synthesis, preventing cross linking and weakening the cell wall
2) Blocks action of transpeptidase enzyme that cross link PG
Are glycopeptides bactericidal or bacteriostatic?
Bactericidal
Are cephalosporins bactericidal or bacteriostatic?
Bactericidal
Are penicillins bactericidal or bacteriostatic?
Bactericidal
Give an example of a glycopeptide and its route of administration?
Vancamycin IV only
Which bacteria is vancomycin effective against?
Gram positive bacteria
Why should vancomycin be used with caution in patients with kidney failure?
Vancomycon is excreted via kidneys so it can build up in patients with kidney failure => more kidney failure
When is vancomycin given orally and why?
Treatment of severe C diff. It is not absorbed from the gut wall so is acting topically on the lumen
Which antibiotics inhibit protein synthesis by binding to bacterial ribosomes to prevent peptide formation?
Macrolides
Aminoglycosides
Others (Clindamycin, chloramphenical, tetracyclines)
Are macrolides bactericidal or bacteriostatic?
Bacteriostatic as when the antibiotic is removed from the ribosome, usually protein synthisis returns to normal.
Are Aminoglycosides bactericidal or bacteriostatic?
Bactericidal
Give 3 examples of macrolide antibiotics?
Erythromycin, clarythromycin and azithromycin
How are macrolides excreted?
Liver, billary tract and into the gut
Which macrolide is safe in pregnancy?
Erythromycin
When are macrolide antibiotics used?
Treating infections caused by intracellular organisms (lipophillic)
Treating infection caused by microorganisms without a proper cell wall (mycoplamsa and chlamydia)
Alternative for some infections in penicilin allergic patients
Give a example of an aminoglycoside antibiotic and the route of administration?
Gentamycin IV only as its not absorbed from the gut
How does gentamycin work?
Binds to 30S ribosomal subunit causing misreading of the codon and incorrect amino acids being added to teh peptide chain
What are aminoglycosides mainly used to treat?
Gram negative aerobic organisms eg coliforms and pseudomonas
How is aminoglycosides excreted?
Kindey into urine
Gentamycin has a narrow therapeutic index. What can toxicity cause?
Damage to the kidneys and CN 8 impairing balence adn leading to deafness
What is clindamycin used for?
2nd line treatment for Staph and strep infections esp in penicillin allergic patients
Active against true anaerobes
What is chloramphenicol used for?
Topical in eye infections
Are tetracyclines bacteriostatic or bactericidal?
Bacteriostatic
What is tetracycline used for?
Treating bacteria without a cell wall
Sometime used in penicillin sensitive patients
How are clindamycin and tetracyclines excreted?
Liver, billary tract and gut
Give 3 groups of antibiotics that act on bacterial DNA?
Metronidazole
Cotrimoxazole
Floroquinalones
How does metronidazole work?
Causes strand breakage of DNA
What is metronidazole used for?
Infections caused by true anaerobes and protoza
Used first line in moderate C diff
How can metronidazole be administered?
PO or IV
How does cotimoxazole work?
Inhibits bacterial folic acid synthesis
How is cotimoxazole administered?
PO or IV
How is cotimoxazole excreted?
Kidney and urine
Is cotrim safe in pregnancy?
From the 4th month onwards
How do floroquinolones work?
Interact with topsomerases (enzymes responsible for the super coilding and uncoiling of bacterial DNA)
This means the bacterial can no longer replicate
Are floroquinolones bacteriostatic or bactericidal?
Bactericidal
Why is use of floroquinalones restricted in Tayside?
To try to reduce risk of C diff. They are very broard spectrum
How are floroquinalones excreted?
Kidney and urine
Give 2 examples of floroquinalones and their route of administration?
Ciprofloxacin PO and IV
Levofloxacin IV only
What is levofloxacin used for?
Severe CAP when penicillin allergic
What are the common side effects of antibiotics?
GI = nausea, vomiting, diarrhoea, failure of COC pill
Kill normal gut flora allowing overgrowth of C diff
What can promote bacteria becoming resistant to antibiotics?
Giving antibiotics at sub optimal does for prolonged periods
What are the specific side effects of Vancomycin?
Kidney damage and red mans syndrome
WHat are the specific side effects of tetracyclines?
Permanent staining of bones and teeth in children
What are the specific side effects of metronidazole?
Interacts with alcohol. No alcohol allowed
What are the specific side effects of floroquinalones?
Weakens tendons => tendon rupture
May damage joints in children
May cause seizures
If a patient is true penicillin allergic, what other antibiotics should be avoided?
Cephalosporins
Which antibiotics should NOT be given in pregnancy?
Gentamycin, tetracyclin and floroquinalones
Which antibiotics should be avoided in the first 3 mouths of pregnancy?
Cotrim and metronidazole
How can bacteria acquire resistance to antibiotics?
1) Genetic de novo mutation
2) Transfer of DNA from another bacteria with resistance mutation
How frequently do bacteria replicate?
Every 20 minutes. This means mutation occurs more frequently
How do bacteria transfer DNA with resistance mutations?
1) Transformation
2) Conjugation
3) Transduction
What is transformation?
Bacteria die and cells break apart, free floating DNA can be absorbed by other bacteria and incorporated into their DNA. This DNA may contain genes coding for antibiotic resistance
What is conjugation?
Bacteria contain extra chromosomal material called plasmids. These can carry resistance genes.
Two bacteria in close proximity can forma pilus/conjugation tube between their cells
Plasmid replicates and one copy is transfered via the pilus to the other bacteria.
What is transduction?
Bacterial DNA is transferred to another inside a virus that infects the bacteria.
1) Bacteriophages infect a bacterium and take of the genetic processes forming a prophage to produce more phage
2) During this process bacterial DNA, which may code for resistance can be incorporated into the new phage DNA
When the host cell dies, phages are released from the dead cell and can be transferred to other bacterial cells
What are the virus’ called which enable transduction?
Bacteriophage or phage
What are the mechanisms of antibiotic resistance?
1) Altered antibiotic target binding site
2) Destruction/inactivation of antibiotic
3) Increased efflux (antibiotics enter cells through porins, efflux pumps are channels that actively export antibiotics out of the bacterial cell
How is MRSA resistant to penicillin?
Penicilins bind to PBP (penicillin binding protein) in the bacterial cell wall. A mutation is staph aureus results in abnormal PBPs and penicillin can no longer bind
How can bacteria destroy or inactivate antibiotics?
Beta lactamases or cephalopsporinases
Some gram negatives can produce extended spectrum beta lactamases
