Antibiotics Part 2 Flashcards
1
Q
Describe features of Vancomycin
A
- It is a glycopeptide antibiotic which is ultrabroad spectrum for gram positive bacteria.
- Delivered IV but has difficult pharmacodynamics
- Less effective than fluclox for MSSA but used in patients who have MRSA or can’t take fluclox.
- Active against MRSA, streptococci, MSSA,
- Main issue in clinical use is underdosing
Not active against coliforms, difficult gram negatives or anaerobes
2
Q
What are the diffierent toxic effects seen with vancomycin
A
- Nephrotoxicity (with high doses)
- Red-man syndrome if injected rapidly (anaphylactoid syndrome)
- Ototoxicity
- Therefore theraputic drug monitoring is undertaken due to its narrow theraputic range
3
Q
What gene gave rise to S.aurus resistance and what drug can be used in MRSA
A
- MecA gene inherited from S. fleurettii
- Vancomycin is used
4
Q
Describe features of Gentamicin
A
- It is an aminoglycoside antibiotic with very broad spectrum which can only be delivered IV
- Principally useful against gram negatives so useful with intra-abdominal infections and UTI
- Low rates of resistance in community but not uncommon
Active against most gram negatives
5
Q
Explain the mechanism of action of aminoglycosides
A
- Reversibly binds to the 30S ribosome which causes a bacteriostatic action, prolonging the post-antibiotic effect.
- It has a bactericidal action by acting on the cell membrane. Results in rapid lysis early in dosing intervals with high doses
6
Q
What are the toxic side effects of aminoglycosides
A
- Nephrotoxicity
- Ototoxicity (hearing loss, loss of balance, oscillopsia)
- Neuromuscular blockage (usually only significant in patients with myasthenia gravis - AVOID in these patients)
7
Q
What is the dosing regimen for aminoglycosides
A
- Once daily dosing. High initial dose to take advantage of rapid killing.
- Leave long dosing interval (24-48hrs) to minimuse toxicity
- Make sure to measure trough level between doses to ensure drug is not accumulating
- Give for 3 days only
8
Q
What are personal risk factors for resistance?
A
- Antibiotic consumption within the last 6 months
- Overnight stays in hospitals
- Visiting countries with high incidence of drug resistance
- This resistence may occur for many months after acquired
9
Q
Describe features of Macrolides
A
- Class of antibiotics with a good spectrum of activity against gram positives and respiratory gram negatives
- Active against atypicals such as legionella, mycoplasm or chlamydia
- Ecellent oral absorption
- Examples include erythromycin, azithromycin and clarithromycin
10
Q
What are the main targets of antibiotics
A
- Cell wall biosynthesis (targeted by betalactams and vancomycin)
- Protein biosynthesis (argeted by macrolides, aminoglycosides and tetracyclines)
- DNA and RNS synthesis (Rifampin and quinolones)
- Folate metabolism (trimethoprim)
11
Q
What are the main side effects and drug interactions of macrolides
A
- Side effects are diarrhoea and vomiting, QT prolongations and hearing loss with long term use.
- Resistance among typical pathogens is common but in atypical pathogens is rare.
- Interacts with simvastatin so avoid co-prescription, atorvastatin and warfarin.
12
Q
Describe features of clindamycin
A
- Similar to macrolides as it has same mechanism, good oral absorptions and principally active against gram positives
- However no action against aerobic gram negatives or atypicals but does have excellent activity against anerobes so often used in abscesses
- It is highly effectice at stopping exotoxin production so added alongside other antibiotics in toxic shock syndrome and necrotising fasciitis
13
Q
Name and describe the C.differgic antibiotics
A
- These are antibiotics that dramatically disturb the colonic flora. C.diff forms spores which are difficult to erradicate from hospitals
- 4Cs are the common causes but all antibiotics can cause C.diff:
- Clindamycin
- Co-amoxiclav
- Cephalosporins
- Ciprofloxacin
14
Q
Describe features of tetracyclines
A
- Active against MSSA, streptococci and atypical organisms
- Relatively non doxic but avoid in children and pregnant women as it can cause bone abnormalities and tooth discolouration
15
Q
Describe features of Quinolones
A
- Broad spectrum, bactericidal antibiotics which targert Dna/RNS synthesis
- Excellent oral bioavailability
- Agtive gainst many atypical pathogens
