in clinical trails whats the duration of PHASE IV ?

Clinical Trials phase 1 = Safety, ADME, Healthy bioactivity, volunteers or subj. w/ drug-drug interaction indications Length (per phase) 20-80 6-12 mos phase 2 = Sho-term side Subjects with effects & efficacy indications Several hundred 1-2 yrs phase 3= Safety & efficacy Basis for labeling, new formulations New indications, QoL, surveillance Subjects with Hundreds-indications thousands Subjects with indications 2-3 yrs phase 4 = Safety & efficacy Basis for labeling, new formulations New indications, QoL, surveillance Subjects with Hundreds-indications thousands Subjects with indications indefinite time and on going ref : kd tripathi 8th ed