Changes

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

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==

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.

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

==Side Effects and Contraindications==

==Side Effects and Contraindications==

* Penicillins containing procaine musn't be given I.V. or with sulphonamides (they antagonise the action of sulphonamides.)

* Penicillins containing procaine musn't be given I.V. or with sulphonamides (they antagonise the action of sulphonamides.)

* Care must be taken when giving narrow spectrum penicillins to Guinea Pigs, Rabbits, Gerbils, Hamsters and Chinchillas as they can result in '''fatal ''Clostridium difficile'' colitis'''.

* Care must be taken when giving narrow spectrum penicillins to Guinea Pigs, Rabbits, Gerbils, Hamsters and Chinchillas as they can result in '''fatal ''Clostridium difficile'' colitis'''.