An O/W cream contains 100 mg prednisolone and rice starch.

The replacement by wheat starch poses no single problem. The crucial question is the why of the addition of rice starch. Since the rice starch will saturate its water absorbing capacity with the cream, it cannot be argued that the addition is intended to adsorbate wound fluid.  

We must say   that the doctor is prescient and realizes that a homogeneous distribution of 100 mg prednisolone in a viscous cream base is not easy. He requires that you dilute the 100 mg prednisolone homogeneously with diluent in this case rice starch to e.g. a total quantity of 5 G. This mixture is then homogenous mixed with 95 g cream base. An operation with the Unguator can only promote the homogeneity strongly.