Changes

For drugs to act upon the body they must be able to exert some chemical influence upon a cell to result in a physiological response. They are capable of doing this by binding to a target molecule (usually proteins).

For drugs to act upon the body they must be able to exert some chemical influence upon a cell to result in a physiological response. They are capable of doing this by binding to a target molecule (usually proteins).

There are four main kinds of targets for the drugs to bind to:

There are four main targets which drugs to bind to:

* '''Receptors''' - these are protein molecules that are capable of responding to endogenous chemical signals. They are usually found on the cell membrane, in the cytoplasm or on the nucleus and other organelles.

* '''Receptors''' - these are protein molecules that are capable of responding to endogenous chemical signals. They are usually found on the cell membrane, in the cytoplasm or on the nucleus and other organelles.

* The biological response of resulting from an agonist is proportional to the number of receptors occupied. The size of a response can be measured  and plotted against the dose/concentration of the agonist. As the size of a response normally increasee in a non-linear manner (until the maximum is reached) the response is normally plotted against the log of the concentration.

* The biological response resulting from an agonist binding is proportional to the number of receptors occupied. The size of a response can be measured  and plotted against the dose/concentration of the agonist. As the size of a response normally increases in a non-linear manner (until the maximum is reached) the response is normally plotted against the log of the concentration.

  '''Please Insert Appropriate Graphs'''

  '''Please Insert Appropriate Graphs'''

From these graphs two figures can be achieved, the '''ED50''' or '''EC50'''. The ED50 is the effective dose at which 50% of a maximal response occurs or 50% of individuals respond. The EC50 is the same but is the effective concentration. Agonists with higher affinities will have a lower concentration and so EC50 than an agonist with a lower affinity. The first drug is therfore said to be more '''potent'''.

From these graphs two figures can be achieved, the '''ED50''' or '''EC50'''. The ED50 is the effective dose at which 50% of a maximal response occurs or 50% of individuals respond. The EC50 is the same but is the effective concentration. Agonists with higher affinities will have a lower concentration and so EC50 than an agonist with a lower affinity. The first drug is therfore said to be more '''potent'''.

The difference between the full and partial agonist is it's '''efficacy'''. This is defined as the strength of the tissue response that results from the formation of a agonist-receptor complex. The efficacy of the partial agonist is lower than that of the full agonist.  

The difference between the full and partial agonist is its '''efficacy'''. This is defined as the strength of the tissue response that results from the formation of a agonist-receptor complex. The efficacy of the partial agonist is lower than that of the full agonist.  

It is still unclear why molecules that are chemically very similar have differing efficacies. Only now are the mechanisms behind it being gradually understand. This however doesn't mean that we ignore efficacy. It is of great practical importance as some drugs of equal affinity for a specific receptor may have widely differing efficacy.

It is still unclear why molecules that are chemically very similar have differing efficacies. Only now are the mechanisms behind it being gradually understand. This however doesn't mean that we ignore efficacy. It is of great practical importance as some drugs of equal affinity for a specific receptor may have widely differing efficacy.

===Inverse Agonists===

===Inverse Agonists===