Dose-response relationships

Dose-response relationships:
The relationship between the amount of drug given and the response produced  fundamental concern about the minimum dose to be used and the maximum response that can be elicited

Most dose-response curves plotted on a graph have 3 phases:
1) Initial phase – at low doses, increasing does is still too low to elicit much of a response  curve is relatively flat
2) Increase in dose  increase in response; curve is steeper
3) Point is reached in which increasing dose does not elicit any more response  curve is flat

Dose-response curves plotted on a graph show two characteristics of drugs:
1) Maximal efficacy:
• defined as the maximal effect that a drug can produce
• it is the point that the dose-response curve flattens
• the dose-response curve of drugs in same therapeutic class will flatten at different levels

2) Relative potency:
• potency is the concentration/amount of a drug that is needed to elicit a response
• potency is related to the relative position of the dose-response curve on the x axis
• two drugs may have same maximal efficacy, but need different doses to reach it
• those with needing a higher dose will have there dose-response curve more to the right on the graph
• often expressed as the dose of a drug that is needed to achieve 50% of the desired therapeutic effect

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