The affixes called niṣṭhā come after a verbal root used in the sense of past time.,
The affixes क्त and क्तवतु are निष्ठा 1.1.26. As कृ + क्त = कृतम् 'made'; कृ + क्तवतु = कृतवत्,1st. sing. कृतवान् 'done'; so also भुक्तम् and भुक्तवान् 'eaten'.
Vart:- The Nishtha affixes come when adi-karma is meant. For a fuller description of what constitutes adi-karma see sutra 3.4.71, and the illustrations under it. Thus प्रकृतः कटं देवदत्तः, प्रकृतवान् कटं देवदत्तः ।,