<prompt> in clinical trails whats the duration of PHASE IV ?3-5 years1-3yrs1yrindefinite duration of time  <response>: 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 