Abbrevation: t1/2. Generally the time interval, in which half of a raw material is disintegrated or converted. This term is originally used for the decay of radioactive nuclides but increasingly also for the pharmacokinetic of medicaments, representing the time required for half of the substance to be removed from an organism. Knowing the half life permits with knowledge of the startup dose and the distribution volume an estimation of the possible detection duration of an active substance, i.e. the time, at which the active substance concentration falls below the detection limit of a certain analytic method.
Since the formed metabolites are converted for their part also with a defined half life, which is often clearly longer than those of the original substance, it permits to their proof a partial clearly longer proof duration.
Also for adjustment for a certain constant active substance level for long-term therapies the knowledge of the half lefe is necessary.