No drug stays in your system forever.
For example, in nuclear physics, half-life refers to radioactive decay.)
More generally, the study of half-life reflects a measure of pharmacokinetics.
GP Kidd / Getty Image
Pharmacokinetics refers to the study of how a drug moves through the bodyits entry, distribution, and elimination.
Both pharmacists andphysiciansare concerned with a half-life as a metric.
In other words, the more widely the drug distributes in your body, the longer it half-life.
Furthermore, this same drug’s half-life is inversely dependent on its clearance from your body.
Of note, drugs are cleared by both your kidneys andliver.
First-order kinetics means that the elimination of the drug directly depends on the initial dose of the drug.
With a higher initial dose, more drug is cleared.
Most drugs follow first-order kinetics.
Conversely, drugs withzero-order kineticsare independently cleared in a linear fashion.
Alcohol is an example of a drug which is eliminated by zero-order kinetics.
Older people usually have relatively more adipose tissue than do younger people.
Age, however, has a more limited effect on hepatic and renal clearance.
On a related note, people living with obesity have a higher volume of distribution, too.
