Onset, peak, and duration
In addition to absorption, distribution,
metabolism, and excretion, three other factors play important roles in a drug’s
onset of action
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
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.