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
