Charles Ellicott Commentary 2 Kings 14:5

"And it came to pass, as soon as the kingdom was established in his hand, that he slew his servants who had slain the king his father:" — 2 Kings 14:5 (ASV)

As soon as the kingdom was confirmed — that is, as soon as he was firmly established on the throne; as soon as he felt his power secure (Compare to 1 Kings 2:46).

Slew ...—slain. —Literally, smote ... smitten.