MARIELLY SIERRA MERCADO, M.D. appears in the CMS NPPES registry as a Internal Medicine Physician provider holding M.D. credentials at UNIVERSITY DISTRICT HOSPITAL, SAN JUAN, PR, 00935, with a listed phone of (787) 754-0101. NPI 1013258482 was issued on 03/11/2013. Because NPPES data is self-reported by the provider and refreshed monthly, the address, phone, and specialty reflect what SIERRA MERCADO 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 6,806 prescription claims written by this provider, covering 442 Medicare beneficiaries and totaling roughly $1.7 million in drug spend, split 54% brand-name and 46% generic by claim count. 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.

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.