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[[Image: Polymyxin B.png|thumb|right|250px|The Core Structure of Polymyxin B (Cpoyright WikiMedia Commons)]]
[[Image: Polymyxin B.png|thumb|right|250px|The Core Structure of Polymyxin B (Copyright WikiMedia Commons)]]
This type of antibiotic are basic cyclic decapeptides. The commonly used drugs are '''Polymyxin B and E (Colistin)'''.
This type of antibiotic are basic cyclic decapeptides. The commonly used drugs are '''Polymyxin B and E (Colistin)'''.
==Mechanism of Action==
==Mechanism of Action==
This group of antibiotics function by binding to the cell membrane and then making it permeable. This will lead to swelling of the cell and then apoptosis, resulting in the antibiotic being very bactericidal and a concentration dependent killer. As they are cationic basic proteins they also act like detergents.
This group of antibiotics also have another interesting function; they are capable of binding to bacterial endotoxin (LPS) and therefore neutralising it. It is this secondary function, which is often why vets use these antibiotic as they are very useful in treating animals with '''endotoxic shock'''.
==Spectrum of Activity==
==Spectrum of Activity==
* Action is potentiated by cationic detergents (Chlorohexidine) and by chelating agents (EDTA).
* Action is potentiated by cationic detergents (Chlorohexidine) and by chelating agents (EDTA).
* Have a synergistic action with other antibiotics that are able to penetrate the cell wall of gram negatives.
* Have a synergistic action with other antibiotics that are able to penetrate the cell wall of gram negatives.
* Their actio is inhibited by the presence of cell debris (pus) and divalent cations.
* Their action is inhibited by the presence of cell debris (pus) and divalent cations.
* Able to neutralise bacterial endotoxin.
==Pharmacokinetic Considerations==
==Pharmacokinetic Considerations==
* Systemic use can lead to nephrotoxicity, especially in dogs.
* Systemic use can lead to nephrotoxicity, especially in dogs.
* '''Must not use in renal failure patients''' - as will accumulate in the kidney.
* '''Must not use in renal failure patients''' - as will accumulate in the kidney.
* In man it has been known to be neurotoxic and have neuromuscular blocking effects.
* If sulphate salts are used in the drug preperation, pain and necrosis can occur at the injection site.
* If sulphate salts are used in the drug preperation, pain and necrosis can occur at the injection site.
{{Learning
|Vetstream = [https://www.vetstream.com/canis/Content/Generic/gen00589.asp Polymyxin B]}}