Onset, peak, and duration
In addition to absorption, distribution, metabolism, and excretion, three other factors play important roles in a drug’s pharmacoki-netics:
· onset of action
· peak concentration
· duration of action.
The onset of action refers to the time interval from when the drug is administered to when its therapeutic effect actually begins. Rate of onset varies depending on the route of administration and other pharmacokinetic properties.
As the body absorbs more drug, blood concentration levels rise. The peak concentration level is reached when the absorption rateequals the elimination rate. However, the time of peak concentra-tion isn’t always the time of peak response.
The duration of action is the length of time the drug produces its therapeutic effect.