Antimicrobial chemotherapy- General Principles of Clinical Flashcards
What are mutagenic antimicrobials?
induce mutation in foetal chromosomes
What are teratogenic mutations?
associated with congenital abnormalities (metronidazole and trimethoprim)
What are safe antibiotics during pregnancy?
penicillins, cephalosporins and urinary infection treatment, nitrofurantoin
What is prophylaxis?
sort of treatment that you would like to consider when you would like to treat patients in order to prevent further infection to occur
Dosage should cover the period of risk only
(usually one dose pre-operatively).
Not be extended to avoid selecting out resistant organisms.
What does therapy involve?
When the organism(s) causing infection is not known,
empirical antimicrobial therapy
may have to be commenced if urgent treatment is required.
This should take into account the site and type of infection as well as
the likely causative organisms and their common antimicrobial susceptibility patterns.
The treatment prescribed should always be reviewed once the results
of culture and antibiotic sensitivity tests become available.
When would it be necessary to use antimicrobials in combination?
To cover mixed infection by more than one organism.
Because two antimicrobials sometimes have an enhanced effect together.
To minimise the development of resistant strains to any one agent
(especially in the treatment of TB or HIV).
What are the three possible outcomes when antibiotics are used in combination?
Their effects are additive.
They are antagonistic and their combined effect is less than the sum of their individual contributions.
They are synergistic and their combined effect is
greater than the sum of their individual contributions.
What is a common example of antibiotics in combination?
The most common example of this is the
combination of penicillin and gentamicin.
(streptococcal infective endocarditis).
Penicillin breaks down the streptococcal cell wall,
and allows gentamicin access to the ribosome.
Rules for combinations of drugs?
1) The combination of two cidal drugs or
of two static drugs is additive or synergistic.
#2) The combination of one static and one cidal drug
may result in antagonism. (cancel each other out)
Why is penetration to site of infection important?
Antimicrobial with high serum concentrations,
appropriate spectrum and excellent safety profile,
but unable to penetrate to the site of infection
is of little use in clinical practice.
Why is monitoring important?
monitoring levels in blood to make sure it doesn’t overcome threshold where this antibiotic is no longer clinically effective by causing toxicity.
What are the two main reasons for monitoring serum levels of an antimicrobrial?
To ensure that therapeutic levels have been achieved.
To ensure that levels are not so high as to be toxic.
How are gentamycin and vancomycin monitored in the serum?
Antibiotics most commonly measured in serum are
gentamicin (or other aminoglycosides) and vancomycin.
Vancomycin is usually monitored by measuring a trough level immediately before the
dose is given to ensure it is not too high.
Once a day dosing with gentamicin is now common and the interval between doses
is adjusted on the basis of levels measured 6 to 14 hours post dose.
What is the E test?
The simplest way to measure the
M.I.C.
(Minimum Inhibitory Concentration)
of one antibiotic against one organism is with E-test.
A commercially available paper strip which has a gradient of antibiotic concentration absorbed into it.
The M.I.C. of the organism can be read directly from the point where organism growth intersects the strip.
What factors influence outcome in E test?
In vitro laboratory test gives only a prediction
whether the infection is likely to be cured by the antibiotic in question.
Factors influencing the outcome in practice include:
route of administration, dosing schedule, penetration of antibiotic to the target site and interactions with other drugs. E test.
