308 The safe and effective use of antimicrobials Flashcards
Amoxicillin
Used to treat s.pyogenes (sore throat, skin infections), pneumococcal infections (respiratory tract), and coliform infections (UTI)
Mechanism: inhibition of bacterial wall synthesis
Oral Bioavailability Good
Protein binding 20%
Metabolism Not significant
Half-life 1 hour
Excretion Urine
Dose: 250-1000mg 8 hourly
Name some Beta-lactam antibiotics
Penicillins:
Penicillin
Penicillin G
Penicillin V
Amoxicillin
- co-amoxiclav
Flucloxacillin
Piperacillin
Cephalosporins:
Cephalexin
Cefuroxime
Carbapenems:
Meropenem
What is the penicillin used for Staph aureus infections?
Flucloxacillin
What is the penicillin used ofr pseudomonas infections?
Piperacillin
What are the important points to ask when taking a beta-lactam allergy history?
When was it?
What happened – time course and severity?
What was the drug?
Might they have had glandular fever?
Have they had a (different) beta-lactam since?
-Good history of anaphylaxis – avoid all beta-lactams
-Weak history or of delayed reaction – consider re-challenge
Clarythromycin
A macrolide. Used instead of amoxicillin if the patient has an allergy. It treats the same things but is also active against cell-wall deficient bacteria (e.g. Chlamydia) which cause pneumonia and genitourinary infections
Mechanism: Inhibition of protein synthesis in the bacterial ribosome (50S subunit)
Oral Bioavailability Good
Protein binding High
Metabolism Hepatic
Half-life 1~6 hours
Excretion Metabolites in bile
Dose: 500mg 12 hourly
Adverse side effects: Adverse effects
Nausea and diarrhoea. May alter cardiac conduction - arrhythmias
Interactions: Inhibits enzymes (cytochrome p450 enzymes) involved in the metabolism of other drugs
Vancomycin
A glycopeptide active against gram-positive strains including MRSA
Mechanism: Inhibits bacterial cell wall (peptidoglycans) formation by a different target to beta lactams
Oral Bioavailability Very low (given IV)
Protein binding 50%
Metabolism None
Half-life 4-8 hours
Excretion Urine
Adverse side-effects: Nephrotoxic, Ototoxic
Dose: 500-1500mg 12 hourly, Narrow therapeutic window. Dose by drug levels in blood
Interaction: Other ototoxic or nephrotoxic drugs
What does MRSA stand for?
Methicillin Resistant S. aureus
Doxycycline
A tetracycline. Good activity against Gram positives (streps and staphs), some Gram negs (haemophilus). Also active against cell-wall deficient bacteria (e.g. Chlamydia) which cause pneumonia and genitourinary infections. Poor against Enterobacteriaceae, anaerobes
Used for skin, resp tract, and genital tract.
Seems to have low C diff risk
Oral Bioavailability Good
Protein binding Moderate
Metabolism None
Half-life 6-12 hours
Excretion Urine and bile
Mechanism: Inhibition of protein synthesis in the bacterial ribosome (30S subunit)
Dose: 100-200mg daily
Adverse side-effects: Dyspepsia, Photosensitivity, Avoid in pregnancy / children (tooth damage)
Interactions: Competes for protein binding
Warfarin, digoxin
Nitrofuratoin
A nitrofuran – only important drug in class. Wide spectrum – esp E. coli and some other enterobacteriaceae, also enterococci, staphs, some streps
Used for lower urine infections only – too little tissue penetration elsewhere.
Seems to have low C diff risk.
Oral Bioavailability Good
Protein binding Moderate
Metabolism None
Half-life 1 hour
Excretion Urine
Mechanism: Complex. Damages bacterial DNA
Adverse side effects: V well tolerated
Safe in early pregnancy – avoid late
Avoid in renal impairment – peripheral neuropathy, doesn’t penetrate urine if eGFR low
Dose: 50mg qds
No major interactions
What does VRE stand for?
Vancomycin Resistant Enterococci
What does ESBL stand for?
Extended Spectrum Beta-lactamase
What does CPE stand for?
Carbapenemase producing Enterobacteriaceae
What does KPC stand for?
Klebsiella producing carbapenemases
What factors reduce resistance?
Giving less antibiotics
Using antibiotics correctly
