When gentamicin is given , its half life is 2-3 hours but it accumulates in kidney and its half life is prolonged to 53 hour. This half life is called as:

Terminal half life: With prolonged dosing (or with high drug concentrations), a drug may penetrate beyond the central compament into "deep" or secondary body compaments that equilibrate only slowly with the plasma. When the infusion or dosing stops, the drug will be initially cleared from plasma as expected but will eventually drop to a point at which net diffusion from the secondary compaments begins, and this slow equilibration will produce a prolongation of the half-life of the drug, referred to as the terminal half-life.