To amend title XVIII of the Social Security Act to prohibit prescription drug plan sponsors and MA-PD organizations under the Medicare program from retroactively reducing payment on clean claims submitted by pharmacies.

Improving Transparency and Accuracy in Medicare Part D Spending Act This bill amends title XVIII (Medicare) of the Social Security Act to prohibit Medicare Prescription Drug Plan sponsors from retroactively reducing payment on clean claims submitted by pharmacies. (A "clean claim" is a Medicare claim that is free of defects such as incomplete documentation.)