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The penicillins also inactivate an inhibitor of autolytic enzymes present in the cell wall, thus resulting in lysis of the bacterium.

The penicillins also inactivate an inhibitor of autolytic enzymes present in the cell wall, thus resulting in lysis of the bacterium.

Due to the lytic nature of the group of drugs they are considered to be '''bacteriocidal''' (ie kill bacteria).

Due to the lytic nature of the group of drugs they are considered to be '''bacteriocidal''' (ie kill bacteria) and time dependent killers.

 

==Spectrum of Activity==

==Spectrum of Activity==

Over the years different sub-groups of Penicillins have been developed; this is because many bacteria have developed '''beta-lactamases''' which will therefore reduce the action of the antiobiotic

Over the years different sub-groups of Penicillins have been developed; this is because many bacteria have developed '''beta-lactamases''' which will therefore reduce the action of the antibiotic.

'''Natural Penicillins''' - benzylpenicillin or Penicillin G

'''Natural Penicillins''' - benzylpenicillin or Penicillin G

'''Anti-staphylococcal Penicillins''' - Cloxacillin

'''Anti-staphylococcal / IsoxazoylPenicillins''' - Cloxacillin

* Narrow Spectrum

* Narrow Spectrum

* Resistant to beta-lactamase producing Staphylococci, and so active against gram positive bacteria.

* Resistant to beta-lactamase producing Staphylococci, and so active against gram positive bacteria.

'''Extended Spectrum Penicillins''' - Ticarcillin

'''Extended Spectrum Penicillins / Carboxypenicillins''' - Ticarcillin

* Broad Spectrum

* Broad Spectrum

* Active againts gram positive species except those with beta-lactamase enzymes.

* Active againts gram positive species except those with beta-lactamase enzymes.

If a beta-lactamase inhibitor ('''Clavulanic acid''') is added to the drug formulation, the spectrum of most sub-groups is extended.

If a beta-lactamase inhibitor ('''Clavulanic acid''') is added to the drug formulation, the spectrum of most sub-groups is extended.

==Pharmacokinetic Considerations==

==Pharmacokinetic Considerations==

All the sub-groups behave in the same way pharacokinetically.  

All the sub-groups behave in the same way pharacokinetically.  

They are organic acids, hydrophilic and will ionise at physiological pH. They generally have '''poor oral bioavailability''' as they unstable in acid environments. They have a limited volume of distribution (0.2-0.3l/kg), this means the drug is mainly confined to plasma and interstitial space. As the are lipophilic they can't enter cells and won't cross the blood brain barrier, unless it is damaged. They are readily excreted by the kidneys, via tubular secretion in the proximal convoluted tubule. This results in high concentrations of the drug in urine.

They are organic acids, hydrophilic and will ionise at physiological pH. They generally have '''poor oral bioavailability''' as they unstable in acid environments. They have a limited volume of distribution (0.2-0.3l/kg), this means the drug is mainly confined to plasma and interstitial space. As the are hydrophilic they can't enter cells and won't cross the blood brain barrier, unless it is damaged. They have short half-lives of about 0.5 - 1.2 hours. They are readily excreted by the kidneys, via tubular secretion in the proximal convoluted tubule. This results in high concentrations of the drug in urine.

 

 

 

 

 

* '''Carboxypenicillins''' - unstable in acid. Route of admin: IM or IV.

==Side Effects and Contraindications==

==Side Effects and Contraindications==

==Potential Uses==

 

 

|Vetstream = [https://www.vetstream.com/equis/Content/Freeform/fre00352.asp Beta-Lactam Antibacterials]}}