We need to identify who (hospital or manufacture) mixed the medication? 

We have not found an element in Medication to store this information. Our suggestion is to create a new element (CodeableConcept) in Medication called compositionType. As codes we suggest: 

• 272163001 Mixture (qualifier value) to indicate compounded by the hospital.
• 19535007 Original (qualifier value) to indicate it is in its original state from the manufacturer.