antimicrobials Flashcards
What are the MINDME guidelines for antimicrobial therapy?
M: microbiology guidelines used whenever possible
I: indications should be evidence based
N: narrowest spectrum required
D: dosage appropriate to the site and type of infection
M: minimise duration of therapy
E: ensure mono therapy in most situations
What is directed therapy vs. empirical therapy?
directed therapy - base choice of therapy on culture or susceptibility test results
empirical therapy - known common pathogens and resistance patterns (seasonality)
duration should be as short as possible, should not exceed 7 days unless there is proof this length of time is inadequate
Targets of antibacterials?
cell wall synthesis
protein synthesis
DNA- inhibit cell division
other metabolic processes
Factors affecting choice of antibacterial
bacterial factors: what type of organism, how resistant
host factors: site of infection, allergies, renal/hepatic function, concomitant drugs, age
drug factors: spectrum of activity, pharmacokinetics, adverse effects profile, cost
Antibacterial families targeting cell wall bio synthesis
beta-lactams, glycopeptides, cephalosporins
Antibacterial families targeting protein biosynthesis
macrolides, tetracyclines, aminoglycosides, oxazolidinones
Antibacterial family targeting DNA replication and repair
Fluoroquinolones
antibacterial families targeting folate synthesis?
trimethoprim, sulfonamides
antibacterial family targeting cell membrane?
daptomycin
antibacterial families targeting protein synthesis?
linezolid, tetracyclines, macrolides, aminoglycosides
size of virus particles
size range 10-400nm in diameter, most need to be viewed with EM
bacteriophage: 225nm
Can visions exist extracellularly?
Yes, rotavirus exists extracellularly for a few hours in the air
What is a nucleocapsid?
composed of DNA or RNA or a capsid, some viruses may also have an envelope
structural elements of a virus?
- nucleic acid: DNA or RNA, genome can be segmented or circular
- capsid: capsomeres
- envelopes
- spikes
what is the ending for virus order, family, subfamily and genus
O: virales
F: viridae
subfamily: virinae
G: virus
what are the two main systems for classifying viruses
ICTV: international committee on taxonomy of viruses
- main body
Baltimore system complements ICTV, focusses on viral genome and the methods used to synthesise mRNA
How would you classify viruses based on the genome? (5)
dsDNA, ssDNA, dsRNA, ssRNA
- in ssRNA, + strand RNA is identical to mRNA sequence produced by the virus (positive strand)
- strand RNA is complementary to mRNA sequence (negative strand)
common target of antiviral drugs? problems that can occur?
viral polymerase; toxicity can arise when viral polymerase is similar to host cell polymerase
most agents are virustatic - often by the time a viral infection is diagnosed, the virus spread and replication is complete
What does aciclovir target?
viral DNA/RNA synthesis
What does zidovudine target?
viral DNA/RNA synthesis
What do interferons target?
viral protein synthesis
Mechanism of acyclovir?
(prodrug, activated by viral kinases)
= chain terminating agent; added to chain by viral polymerase but lacks 3’OH required for chain extension
Mechanism of zidovudine?
(prodrug, activated by viral kinases)
= NRTI (nucleoside reverse transcriptase inhibitor)
= chain terminator, inhibits viral reverse transcriptase
- has some toxicity: bone marrow suppression, nausea, vomiting, malaise
- resistance is well recognised
- combination/alternating therapy slows development of resistance and minimised toxicity to a particular tissue
ways to monitor antiviral therapy
- measure viral load e.g. by real time PCR
- monitoring mutation rates e.g. by RFLP (restriction fragment length polymorphism) and sequencing
