9.1 Antimicrobial Chemo- prescribing principles Flashcards
Why would you think about prescribing antibiotics?
Therpay with/without direction
Prophylaxis- priamry, antimalairal, immunosupperssed, pre operative surgery, post exposure
Secondayr- to prevent a secodary exposure e.g. PJP
How do you diagnose an infection?
Clinical signs, lab work, screening e.g. qSOFA
What are important patient characteristics to think about before prescribing?
Age Renal function Liver function Immunocomprimised Pregnancy Known allergies
How do you select what antimicrobial to use?
Guideline or individualised therapy ? likely organism empirical therapy or results based therapy Bactericidal vs bacteriostatic drugs Single agent or combination Potential adverse effects
What drug shoudl you use in an elderly woman with postural hypotnsion and e.coli in urin
First of all I wouldn’t treat, use Nitrofurantoin over trimethoprim as its given orally and well tolerated
What are the four main mechanisms antibiotics use for resistance
Enzymatic inactivation of drug
Modified targets for drugs
Reduced permeability to drugs
Efflux of drug
What is chromosomally mediated resistance?
Mutation in gene coding for drug target membrane transport system
Lower frequency of mutation for people who acquire plasmids
Less of a problem clinically
Basis for using multi-drug therapy e.g. TB
What is plasmid mediated resistance?
Plasmids are extra-chromosmal strands of DNA
Replicate independent of cell chromosome
Carry genes for enzyme which degrade antibiotics and modify membrane transport systems
May carry 1 or more resistance genes
What are the medically important resistant organisms
MRSA VRE ESBL CPL Clostridium difficile
What is MRSA?
Resistant to flucloxacillin, often colonsies without infection, causes severe infections including osteomyeitis, endocarditis
What is VRE?
Vancomycin resistant enterococci. Enterococci and intrinsically only sensitive to a limited number of antibiotics, VRE only sensitive to 1 or 2. Grow in the gut of patients exposed to multiple antibiotics, may cause invasive disease in patients with prosthetic devices
What is ESBL?
Extended spectrum presenting beta-lactamase
Confer a range of resistance mechanisms, resistant to beta lactams, also may be reisstant to aminoglycosides and cabapenems
What influnces antibiotic resistance?
Antibiotics used by medical professions, veterinary practices, farming. Patietns survivng longer with mroe medical conditions and hospital contact.
More invasive procedures and prosthetic devices
What would you prescribe to someone who has cellulitis (typically caused by strep. pyogenes, staph aureus, strep. group C or G)
Fluxcloxacillin
What is the go to drug for penicillin resistance?
Vancomycin
What are the different types of hypersensitivty reactions that antibiotics can induce?
Type I- IgE meiated specific immunoglobulin, stimulates bronchospams/circulatory collapse
Type II- beta lactam specific IgG or IgM antibodies bind to circulating blood cell resultin in haematological reactions or interstitial nephritis
Type III- IgG or IgM bind to b-lactam antigens resulting in fever and sickness
Type IV- not antibody mediated but T cells recognise antigen leading to localised inflammation
Someone presents with a staph aureus in surgical wounds, what do you treat it with?
Flucloxacillin
Why might drug therapy fail?
Inadequate dosing Inappropriate route Non-compliance with antibiotics Bacteria walled off in ascess cavity Foreign bodies e.g. surgical implant Poor penetration of drug to infection site e.g. bone and brain
What antibiotics have good biofilm activity?
Rifampicin
Daptomycin
Ceftobiprole
What is meant by the term antibiotic stewardship?
using the right antibiotic for the right indication for the right duration of time
Use an antibiotic only if suspected or proven bacterial infection
Use antibiotics as per guidelines and review with results of microbiology
Review antibiotic prescriptions regularly
Limit use of broad spectrum blind antibiotic therapy
When would you consider switching someone from IV to Oral antibiotics
After 48 hours symptoms are improved and the patient can: Swallow and tolerate fluids Temp 36-38 for at least 2 days Heart rate <100 bpm WCC between 4 and 12
When would you NOT switch antibiotics from IV to oral?
Compromised oral route-diarrhoea, vom, NBM
Continuing sepsis
Special indications- endocarditis, meningitis, staph aureus bactermia, immuno suppression, bone/joint infection, deep abscess, CF, prosthetic infection)
