MARK CASTELLAW, MD appears in the CMS NPPES registry as a Internal Medicine Physician provider holding MD credentials at 8040 WOLF RIVER BOULEVARD, GERMANTOWN, TN, 38138, with a listed phone of (901) 726-0200. NPI 1114928793 was issued on 08/09/2005. Because NPPES data is self-reported by the provider and refreshed monthly, the address, phone, and specialty reflect what CASTELLAW most recently submitted to CMS rather than a vetted directory listing, which is why patients should always confirm the practice is still at this location before scheduling.

Medicare Part D records for calendar year 2023 show 12,791 prescription claims written by this provider, covering 847 Medicare beneficiaries and totaling roughly $1.0 million in drug spend, split 11% brand-name and 89% generic by claim count, with an opioid prescribing rate of 1.7%. These figures capture only Medicare Part D — commercial insurance, Medicaid, and cash-pay prescriptions are not included, and any drug-beneficiary cell under 11 is suppressed by CMS for patient privacy. On the CMS Merit-based Incentive Payment System, this provider earned a Final Score of 76.5182/100 for the 2023 performance year (Quality 70.5342, Cost 66.1931), compared with the national average of 83.1.

Internal Medicine Physician is a high-volume specialty nationwide, with 172,858 enrolled providers across 56 states and an average of 2,716 Part D claims per prescriber, so the context for interpreting these metrics differs meaningfully from a primary-care baseline. Important: PlainDoctor is a directory of publicly available government data, not medical advice, a malpractice database, or a quality rating. Inclusion here does not imply a recommendation, and absence of complaints or sanctions on this page does not mean none exist — always verify credentials through the NPPES NPI Registry, your state medical board, and the ABMS or AOA before making healthcare decisions.