This item is underpowered, especially for its cost. You need to buff that mana drain. Make it take a whole AOE, and/or take by % maybe. Right now, I can't think of many heroes that would gain from this when most late game Int heroes (I'm guessing you would use this on an Int most likely) already have major mana regen and don't need more. I like the concept, but honestly I don't think we need an item like this; at least at this current state. How about making it similar to a Mana Break+Mana Drain kind of spell; dealing damage with the Mana Drain, just not getting that damage back in HP (e.g. - You use Mana Drain on enemy hero; it damages half of __% of target's max Mana pool in damage, and you still drain the full __%). It could work late game, and might be a pretty good item like this, but I just came up with it now, I can't give real numbers. Who knows, maybe it could deal just a certain # but be able to upgrade like a Dagon (but I think it'd make it too similar). Just something to think about, the other posts above had some good ideas as well.
Gotta keep trekking along, making it better and better