Soy formula ?

I recently weaned DS, and I have a possibly dumb question....we initially started him on the similac and then had to go tot he similac sensative (the orage can).  Anyway, we were given 3 cans of the similac isomil (sp?) - the soy formula.  Would there be any harm in using the formula?  I mean, it's about $75 worth of formula I'm going to have to give away if he can't use it, so I just figured I'd check...