Medco Pharmacy and Tier 3 Drugs

On January 1, 2011, my insurance, United Healthcare, who uses Medco as their mail order pharmacy, made the decision that the type of insulin that I use, Novolog is a tier 3 drug.  What does that mean?  That means that instead of last year when I paid $25 for a 3 month supply, I now pay $150 for a 3 month supply.  I noticed that Humalog, which I used to use before I went on an insulin pump, is still a tier 1 drug and still costs only $25 for a 90 day supply.  When I asked why Novolog was bumped up to a tier 3, they said they didn’t know, which I didn’t expect that exact person to know, but somebody had to know and there had to be some sort of documentation out there on why this was bumped to a tier 3.

I still have not been able to find any information, so I am just curious as to why one is considered one thing and the other is not.  I don’t think there is some sort of huge conspiracy here, I just want to know.  Is there a possibility that it could be that more people use Novolog, so that way they charge more for it?  Or they don’t have a good relationship with that manufacturer and they don’t get as good of a deal on it?

Does anybody have any information on this?