Toxic Smite

As you hit the target, it takes an extra 1d8 Poison damage from the attack. Additionally, it must succeed on a Constitution saving throw or become poisoned until the spell ends. At the start of each of its turns until the spell ends, the target takes 1d8 Poison damage and then makes a Constitution saving throw. On a successful save, the spell ends.

Using a Higher-Level Spell Slot. Both the initial and periodic damage increases by 1d8 for each spell slot level above 1.