What is Elimination Half-Life (t1/2)

Elimination half-life (t_1/2) refers to the time it takes for 50% of a drug to be cleared from the bloodstream. It takes approximately eight half-lives to entirely eliminate a drug from the body. 

Every drug has a unique half-life that is dependent on characteristics of the drug (e.g., active metabolites). Knowledge of elimination half-life is important; it is an indicator of how long a drug will produce effects in the body. 

The half-life of a drug can be as short as a few minutes (e.g., drugs used to produce general anesthesia) or as long as several days (e.g., levothyroxine, a drug used to treat hypothyroidism). 

Drugs with long half-lives are dosed less frequently than are drugs with very short half-lives. 

Given the rate of elimination at any given time is proportional to the concentration at that time in first-order kinetics, the elimination half-life can be calculated by dividing the elimination rate constant (0.693) by proportionality constant (k) : 

                                            Elimination Half-Life (t_1/2) = 0.693/k