MARK KASSELIK, MD appears in the CMS NPPES registry as a Nephrology Physician provider holding MD credentials at 2100 WEBSTER STREET, SAN FRANCISCO, CA, 94115, with a listed phone of (415) 923-3456. NPI 1891860193 was issued on 11/21/2006. Because NPPES data is self-reported by the provider and refreshed monthly, the address, phone, and specialty reflect what KASSELIK 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 31 prescription claims written by this provider, covering N/A Medicare beneficiaries and totaling roughly $4K in drug spend. 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.

Nephrology Physician is a mid-sized specialty nationwide, with 10,534 enrolled providers across 55 states and an average of 1,454 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.