RuneScape Classic Wiki
RuneScape Classic Wiki
The main RuneScape Wiki has an article on: Poisoned Iron Spear
The Old School RuneScape Wiki also has an article on Poisoned Iron Spear.

A Poisoned Iron Spear is a poisonous spear which can be made by adding weapon poison to an iron spear. It can be thrown or used within melee combat.

There are no skill requirements to wield it.