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Antimicrobials - Donkey (view source)
Revision as of 11:49, 23 October 2010
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==Introduction==
[[Image:Donkey Europe 2.JPG|thumb|right|200px|<small><center>Image courtesy of [http://drupal.thedonkeysanctuary.org.uk The Donkey Sanctuary]</center></small>]]
Antimicrobial agents should '''only be used in situations where the diagnosis
warrants this'''. The use of antimicrobial agents for relatively trivial infections
encourages the selection of resistant organisms. Irrational use may expose
treated animals to unnecessary risks.
==Dosing==
Successful antimicrobial therapy relies on administering sufficient doses
to effectively suppress ('''bacteriostatic''') or kill ('''bactericidal''') pathogens at
the site of infection so that the host’s defences can eliminate them. For
diseases of unknown cause or attributable to organisms with '''unpredictable
susceptibility''', e.g. [[:Category:Enterobacteriaceae|Gram-negative enteric bacteria]], there is no substitute for
'''bacterial culture and identification of the causative agent'''. A '''Gram stain''' can
be performed immediately on a direct smear and will direct initial therapy
until the laboratory results are obtained.
In the laboratory, the relationship between an antimicrobial drug
and a pathogen is described by the '''minimum inhibitory concentration (MIC)''', the lowest drug concentration that inhibits bacterial growth. The information listed in a culture and susceptibility report is intended to guide
antimicrobial selection but must be interpreted carefully since the testing
does not take into account a number of important factors, such as '''host defences, drug distribution, the infection site environment and the route of drug administration'''.
===Local factors may influence an agent’s activity at the infection site===
* [[Potentiated-Sulphonamides|'''Potentiated sulphonamides''']] achieve adequate concentrations in abscesses but are ineffective in purulent material and necrotic tissue
* '''Rifampin, the [[Tetracyclines|tetracyclines]] and [[Nitroimidazoles|metronidazole]]''' all achieve high concentrations in abscesses and retain their antimicrobial activity in purulent environments
For many drugs, the distinction between bactericidal and bacteriostatic is
not exact and depends on the pathogen involved and the drug concentration attained in the target tissues. A '''bactericidal drug''' ([[Aminoglycosides|aminoglycoside]], [[Penicillins|penicillin]], [[Cephalosporins|cephalosporin]], [[Potentiated-Sulphonamides|potentiated sulphonamide]]) is '''preferable to a bacteriostatic drug''' ([[Tetracyclines|tetracycline]], [[Sulphonamides|sulphonamide]]) for '''neonatal septicaemia, life-threatening conditions and surgical prophylaxis'''.
[[Penicillins]] and [[Cephalosporins|cephalosporins]] are bactericidal but exhibit so-called
'''time-dependent''' (concentration-independent) bacterial killing. <u>Plasma
concentrations of these agents should exceed the MIC of the pathogen
for 50-80% of the inter-dosing interval</u>, and further increases in dose
rate will not increase the bactericidal activity.
[[Aminoglycosides]] exhibit '''concentration-dependent''' bacterial killing and often also produce a
'''prolonged post-antibiotic effect''' (a period after drug concentration falls
below MIC when the bacterial growth remains suppressed), thereby
allowing <u>long interdosing intervals that maximize clinical efficacy and
minimize side effects</u>.
===Combinations of agents are appropriate in only a few situations===
* '''Known synergy''', e.g. a [[Penicillins|penicillin]] or [[Cephalosporins|cephalosporin]] with an [[Aminoglycosides|aminoglycoside]]
* '''Preventing rapid development of bacterial resistance''', e.g. [[Macrolides and Lincosamides|erythromycin]] plus rifampin to treat ''[[Rhodococcus equi]]'' infections
* Extending the spectrum of activity in the initial therapy of '''life-threatening infections'''
* Treatment of '''true mixed''' bacterial infections
===Avoid non-synergistic or antagonistic combinations===
* A bactericidal agent with a bacteriostatic agent. The former require actively dividing bacteria for their activity and the latter stop bacterial growth
* A [[Penicillins|penicillin]] plus a [[Potentiated-Sulphonamides|potentiated sulphonamide]] has minimally additive effects against pathogens but additive effects against the commensal gastrointestinal microflora
==Literature Search==
[[File:CABI logo.jpg|left|90px]]
Use these links to find recent scientific publications via CAB Abstracts (log in required unless accessing from a subscribing organisation).
<br><br><br>
[http://www.cabdirect.org/search.html?q=(title:(antimicrobial)+OR+title:(antibiotic)+OR+subject:(antimicrobials)+OR+subject:(antibiotics))+AND+(ab:(donkey)+OR+title:(donkey))&fq=sc:%22ve%22 Antimicrobials in donkeys publications]
==References==
* Horspool, L. (2008) Clinical pharmacology In Svendsen, E.D., Duncan, J. and Hadrill, D. (2008) ''The Professional Handbook of the Donkey'', 4th edition, Whittet Books, Chapter 12
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