Following the measurement of high amounts of free cortisol in the urine of a patient, a confirmatory test for the diagnosis of Cushing’s syndrome is a test for normal cortisol suppression, through the administration of:

Dexamethasone is the correct choice because it is a synthetic corticosteroid hormone that suppresses the production and release of cortisol. This will help differentiate between primary and secondary causes of Cushing's syndrome.

Option A, B and C are incorrect because they are all synthetic corticosteroid hormones that can potentially increase the levels of cortisol in the body. This can interfere with the results of the confirmatory test, leading to a false diagnosis of Cushing's syndrome.

Furthermore, while these options have anti-inflammatory and immunosuppressive properties, they do not have the same potency and specificity as dexamethasone in suppressing cortisol levels.

It is important to note that the confirmatory test for Cushing's syndrome is performed after high levels of free cortisol have been measured in the urine. Therefore, administering a medication that increases cortisol levels would not be useful in confirming the diagnosis