Principles antibiotic module Flashcards
What are the 2 mechanisms by which antibiotics can treat infections ?
- They can be bactericidal (kill bacteria)
- Or Bacterostatic (inhibit bacterial growth)
What are the 2 types of antibiotic spectrum ?
Broad or narrow
When given orally where are antibiotics absorbed from?
The small intestine and then spread to all parts of the body
What are the 3 ways in which a antibiotic can target a bacteria ?
- Acting on the bacterial cell wall
- Affecting the bacterial ribosome
- Acting on bacterial DNA directly
What are the 3 groups of antibiotics that target the bacterial cell wall ?
- Penicillins
- Cephalosporins
- Glycopeptides
What is the specific mechanism of action of penicillins ?
Inhibits cell wall synthesis by preventing cross-linking of peptidoglycans and is bactericidal
Do penicillins have many side effects ?
no
What is the spectrum of action of the penicillins ?
Ranges from broad to narrow
How are penicillins excreted ?
Via the kidneys
Give some examples of penicillins
Any antiobitc with ‘cillin’ in its name
What are the main drawbacks of penicillins ?
- Some patients are hypersensitive (allergic) to penicillin
- The are rapidly excreted via the kidneys so require frequent dosing (4-6x’s daily)
What molecular structure do all penicillins share ?
A beta-lactam ring
List the 3 forms of penicillin
- Benzylpenicillin (penicillin G, IV)
- Phenoxymethyl penicillin (penicillin V, PO)
- Long-acting penicillin (IM)
Describe the spectrum of action of penicillin
- Gram pos = red
- Gram neg = blue
Penicillin is mainly useful for Clostridum and Streptoccocus
Go over this flow chart to appreciate what penicillins are used for what group of organisms
Describe the spectrum of flucloxacillin action
It has a narrow spectrum acting on only staphylococci and streptococci infections
What type of infections is flucloxacillin used for ?
- Skin and soft tissue infection
- Wound infections
- Cellulitis
- And it is the antibiotic of choice for Staph. Aureus infections
How well is amoxicillin tolerated by the body ?
It is safe and well-tolerated
Why has amoxicillin become less effective over the years ?
Because many organisms now produce beta-lactamase an enzyme which destroys amoxicillin
Describe the spectrum of action of amoxicillin
Describe what co-amoxiclav is and the benefit of this
- It is a combination of amoxicillin and clavulanic acid (beta-lactamase inhibitor)
- The clavulanic acid inhibits the actions of beta-lacatamase enzymes produced by organisms breaking down the beta-lacatase ring ==> this combination extends the range of bacteria which can be treated
Describe the spectrum of action of co-amoxiclav
What is the benefit of using a combination of piperacillin (antibiotic) and tazobactam (beta-lacatamse inhibitor)
- Piperacillin is a broad spectrum penicillin whose range of action is extended even further when used with tazobactam
- It will treat most gram negative bacterial infections including pseudomonas
- The only thing is doesn’t treat is MRSA infection and some EBSL producing organisms (very resistant coliforms)
What antibiotics are the cephalosporins ?
Any antibiotic with ‘cef’ or ‘ceph’ in its name
What is the mechanism of action of cephalosporins ?
The exact same as penicillins ‘Inhibits cell wall synthesis by preventing cross-linking of peptidoglycans and is bactericidal’
How are cephalosporins excreted and do they have many side-effects?
Excreted via the kidneys and have few side-effects
Are the cephalosporins safe in pregnancy ?
Yes
What is the main drawback of cephalosporins and why do many hospitals try to avoid using them?
They are very broad spectrum antibiotics which when used kill of the normal gut bacteria and allow the overgrowth of Clostridium difficile which causes a nasty gastroenteritis
What are the 3 different generations of cephalosporins and there potential uses (although avoided now)
What are the 2 main glycopeptide antibiotics ?
Vancomycin and Teicoplanin
What is the specific mechanism of action of Vancomycin ?
It is bactericidal acting on the cell wall where it binds to the end of the growing pentapeptide chain during peptidoglycan synthesis, preventing cross-linking and weakening the bacterial cell wall
What way does vancomycin need to be administered and why?
IV because it is not absorbed orally
How is vancomycin excreted and why does caution need to be taken in its use ?
Excreted via the kidneys - caution because toxic levels of vancomycin can build up in the blood in patients who have kidnye failure which in turn can cause further kidney damage
Describe the spectrum of action of vancomycin
It is only active against gram positive organisms (NO activity against gram negative)
When may vancomycin be used orally ?
It is not absorbed from the gut but can be given orally to treat C.diff as it acts as a topical on the gut lumen
What are the 3 main groups of antibiotics which inhibit protein synthesis ?
- Macrolides
- Aminoglycasides
- Other
What are the 3 main macrolide antibiotics ?
Erythromycin, Azithromycin and clarithromycin
Think ‘mycin’
How are macrolide antibiotics excreted ?
Via the liver, biliary tract and then into the gut (not the kidneys/urine)
What type of infections are macrolides useful for and why ?
Useful for treating infections where bacteria ‘hide’ from the hosts immune system by getting into the hosts cells. This is because the antibiotics are lipophilic so can pass easily through cell membranes
Are macrolides safe for use in pregnancy ?
Only erythromycin, the others have not been tested
What are the indications for the use of macrolides ?
- Useful for infections caused by intracellular organisms e.g. legionella
- Useful for infections caused by organisms without a cell wall e.g. mycoplasma and chlamydia
- useful for some not all infections where the patient is penicillin allergic
Describe the spectrum of action of macrolides
What is the main aminoglycoside antibiotic ?
Gentamicin
What route dose gentamicin need to be administered and why?
IV (sometimes IM) as not absorbed orally like vanc
What is the specific mechanism of action of gentamicin
- Binds to bacterial ribosomes inhibiting protein synthesis
- It is bactericidal
What type of organisms is gentamicin used for ?
Gram negative aerobic organisms e.g. coliforms and pseudomonas aeruginosa and is used for mainly for serious life-threatining gram negative infections
How is gentamicin excreted ?
Urine/kidneys
What are the main problems with gentamicin use ?
Has a very narrow therapeutic window (fine margin between treating infection and overdosing) ==> blood levels checked regularly
Causes damage to kidneys (nephrotoxic) and VIIIth Cranial nerve resulting in potential:
- Renal failure
- Deafness and disturbance in balance
What are the 3 main ‘other’ antibiotics which inhibit protein synthesis and what are they used for ?
How are all of the ‘other’ antibiotics which inhibit protein synthesis excreted ?
Via the liver and biliary system (same as the macrolides)
What is the main tetracycline used in tayside and how does it specifically work?
Doxycycline - works by inhibiting protein synthesis by attaching to ribosomes and is bacteriostatic
How is doxycyline taken ?
PO
What is doxycyline usefull for ?
- treating infections of bacteria that do not have a proper cell wall (atypical pneumonia organisms)
- treating some infections (mainly chest and skin) in penicillin allergic patients
What are the 3 main groups of antibiotics which act on bacterial DNA ?
- Metronidazole
- Trimethoprim (+/- sulphamethoxazole)
- Fluroquinolones
What is the specific mechanism of action of metronidazole ?
Acts by causing stand breakage of bacterial DNA
What is metronidazole used for ?
- Infection caused by true anaerobes
- Some infections caused by protozoa
What is the specific mechanism of action of trimethoprim
Inhibits bacterial folic acid synthesis
What are the 2 ways in which trimethoprim can be given?
- PO on its own
- Or PO/IV as co-trimoxazole (when its given in combo with sulphmethoxazole)
Describe the spectrum of action of trimethoprim (co-trimoxazole)
Has some activity against both gram negative and gram positive bacteria
How is trimethoprim (co-trimoxazole) excreted ?
Via the urine
When is trimethoprim safe to use in pregnancy ?
After the 4th month onward
What is the specific action of fluroquinolones ?
Interact with topoisomerases which are enzymes responsible for the supercoiling and uncoiling of bacteria. Result is that bacteria cannot replicate. They are bacteriocidal
Why is the use of fluroquinolones restricted ?
Due to risk of causing C.diff esp in elderly patients
What are fluroquinolones the only antibiotic which can be used for…
Orally treating pseudomonas infection
True or false - yuo can get as good blood levels when using PO fluroquinolones as IV ?
True
How are fluroquinolones excreted ?
Urine/kidneys
What are the 2 main fluroquinolones?
Ciprofloxacin and levofloxacin
When may ciprofloxacin or levofloxacin be used ?
What are the general side effects of antibiotics ?
- GI side effects - Nausea and diarrhoea ==> may result in failure of oral contraception
- Can kill off normal gut flora and result in C.diff. Which can cause severe sometimes fatal diarrhoea esp in elderly
- Sub-optimal doses can result in antibiotic resistance
What are the main specific side effects of aminoglycosides (gentamicin)
Nephrotoxic and causes deafness/dizziness
What are the main specific side effects of glycopeptides (mainly vancomycin)
- Vancomycin is nephrotoxic
- Occasionally causes ‘red man syndrome’
What is the main specific side effect of tetracyclines ?
Permanent staining of teeth and bones in children < 12
What is the main specific side effect of metronidazole ?
Interacts with alcohol (vomiting)
What is the main specific side effects of quinolones ?
- Weakens tendons ==> tendon rupture
- May damage joints in children
- May cause seizures
Describe what a true penicillin hypersensitivity reaction is and state the other antibiotic which should be avoided in these patients
what antibiotics are safe to use throughout pregnancy ?
In general Penicillins and Cephalosporins
What antibiotics should be avoided in the first 3 months of pregnancy ?
Trimethoprim and metronidazole
What antibiotics should not be given to pregnant women ?
Gentamicin, tetracycylines and fluroquinolones
