I found a Ninject with Medium trust. But it was not the official one. Somebody updated the package. For anybody else who is looking for Ninject with Medium Trust for .net 4.5 can visit
https://teamcity.bbv.ch/viewLog.html?buildId=987&tab=artifacts&buildTypeId=bt7
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But I could not make that solution working.
So finally I switched to Unity. It works great in Medium Trust environments.