I can see how bean-counting Constitution points for NPCs may not look appealing, so here is another take:Cure disease cures all diseases that the subject is suffering from.
The spell also kills parasites afflicting the target creature. Certain special diseases may not be countered by this spell or may be countered only by a caster of a certain level or higher.
Note: This spell does not prevent reinfection after a new exposure to the same disease.
The reverse form of this spell, cause disease, causes the creature affected by it to suffer from an ailing -and potentially deadly- disease for the next 1d10 days. A successful attack roll is required in this case, and no Saving Throw is allowed. The target suffers a -2 penalty to attack rolls, Armor Class and Saving Throws.
While the disease is in effect, the victim also cannot benefit from natural recovery of Hit Points or Constitution points nor prepare spells or move at running speed.
At the end of each day in which the victim exerted itself (for example by fighting, traveling, working or doing magical research), the character must roll a Saving Throw versus Spells or suffer 1d6 damage points.
Once the duration of the spell is over, the affected character, if still alive, is free of the illness and can start recovering Hit Points, Constitution points, and can again prepare spells.
I like a flat effect that can be used against anything without doing anything to count or keep up with constitution, especially for those foes that don't have an official CON score.