Medicare PBM Accountability Act This bill establishes reporting requirements for pharmacy benefit managers (PBMs) under the Medicare prescription drug benefit and Medicare Advantage, particularly relating to the prices of prescription drugs. Specifically, PBMs must (1) disclose certain information underlying cost performance measurements (e.g., exclusions and terms), and (2) report to prescription drug plan (PDP) sponsors (and to the Centers for Medicare & Medicaid Services upon request) an itemized list of prescription drugs that were dispensed during the previous year and related data about costs, claims, affiliated pharmacies, and other specified information. PDP sponsors may audit PBMs to ensure compliance with this bill's requirements and must annually certify their compliance; PBMs are responsible for any associated civil penalties for violations. In addition, the Government Accountability Office must study federal and state reporting requirements for health plans and PBMs with respect to prescription drug price transparency and recommend ways to streamline these requirements.