Anti-microbial chemotherapy Flashcards
What are the indications for antimicrobials?
- Therapy
□ empiric - without microbiology results
□ directed - based on microbiology results - Prophylaxis
□ Primary
® anti-malarial; immunosuppressed patients
® pre-operative surgical
® post-exposure e.g. HIV, meningitis
□ Secondary
® To prevent a secondary episode e.g. PGP
What should be done to make a clinical diagnosis whne prescribing antimicrobials?
- Diagnosis of infection □ Clinical □ Laboratory □ None (no treatment) - Severity assessment □ Sepsis (qSOFA: syst BP<100, altered mental, RR>22)? □ Septic shock?
What patient charecteristics should be taken into acount when prescribing antimicrobials?
- age
- renal function
- liver function
- immunocompromised
- Pregnancy
- known allergies
What should be considered when selecting an antimicrobial?
- Guideline or “individualised” therapy
- likely organism(s)?
- empirical therapy or result-based therapy
- bactericidal vs. bacteriostatic drug
- Single agent or combination
- Potential adverse events
What is the difference between bacercidal and bacteriostatic antimicrobials?
□ Bactericidal ® e.g.. beta-lactams ® act on cell wall ® kill organisms ® indications include neutropenia, meningitis and endocarditis □ Bacteriostatic ® e.g.. macrolides ® inhibit protein synthesis ® prevent colony growth ® require host immune system to “mop up” residual infection ® useful in toxin-mediated illness
explain single and combination antimicrobial therapies
□ Single ® simpler ® fewer side effects ® fewer drug interactions □ Combination ® HIV and TB therapy ® severe sepsis (febrile neutropenia) ® mixed organisms (faecal peritonitis)
How is the rout of administration decided?
□ Oral bioavailability ® Ratio of drug level when given orally compared with level when given iv ® varies widely ◊ flucloxacillin 50-70% ◊ linezolid 100% □ Oral route if ® Not vomiting ® Normal GI function ® No shock ® No organ dysfunction □ IV route for ® Severe or deep-seated infection ® When oral route is not reliable
What allergic reactions should be thought about when prescribing?
® Immediate reaction ◊ Anaphylactic shock ® Delayed reaction ◊ Rash ◊ Drug fever ◊ Serum sickness ◊ Erythema nodosum ◊ Stevens-Johnson syndrome ® Mostly happens with penicillin and cephalosporins
What GI side effects should be considered when prescribing antimicrobials?
® Nausea, vomiting, diarrhoea
® Clostridium difficile infection
When should candida (thrush) be thought about as a side effect of an antimicrobial?
Broad spectrum penicillin, cephalosporins
When should you worry about side effects to the liver when prescribing antimicrobials?
® All drugs, particularly tetracyclines, TB drugs
® More likely if pre-existing liver disease
When should you worry about side effects to the renal system when prescribing antimicrobials?
® Gentamicin, vancomycin
® More likely if pre-existing renal disease or on nephrotoxic meds
What (and when) should you be worried about with neurological complications?
® Ototoxicity - gentamicin, vancomycin
® Optic neuropathy - ethambutol (TB)
® Convulsions, encephalopathy - penicillin, cephalosporin
® Peripheral neuropathy - isoniazid (TB), metronidazole
What (and when) should you be worried about with Haemotological complications?
® Marrow toxicity
® Megaloblastic anaemia (folate metabolism) - co-trimoxazole
What is the mode of action of penacillins
Inhibition of the cell wall
Give examples of penacillins
® Benzyl Penicillins ® Amoxicillin ® Floxacillin ® Co-amoxiclav ® Piperacillin/ tazobactam
What is the mode of action of cephlasporins?
Inhibition of the cell wall
Give examples of cephlasporins
® Cefradine
® Cefuroxime
® Ceftriaxone/ cefotaxime
® Ceftazidime
What is the mode of action of aminoglycosides?
inhibition of protein synthesis
Give an example of aminoglycosides
Gentamycin
What is the mode of action of macrolides?
Inhibit protein synthesis
When are macrolides used?
Respiratory infections
Give examples of macrolides
□ Clarithromycin
□ Erythromycin
□ Azithromycin
What is the mode of action of quinolones?
Inhibition of nucleic acid synthesis
