Mark C. O'Brien, D.O.
Internal Medicine Physician · Vista, CA
Mark C. O'Brien, D.O. is an internal medicine physician with a practice address in Vista, California, and NPI 1497744247, issued on Oct 14, 2005. Check the license (California 20A6017, as entered in NPPES) on the Medical Board of California; the Medicare figures below come from public CMS files.
- Name
- Mark C. O'Brien
- Credential
- D.O.
- Primary taxonomy
- Internal Medicine Physician 207R00000X
- License number
- 20A6017 CA
Self-reported in NPPES; status is on the state search - Practice location
- 161 Thunder Dr Ste 210, Vista, CA 92083
- Phone
- (760) 216-6500
- Enumerated
- Oct 14, 2005
- Record last updated
- Apr 1, 2025
- Fax
- (760) 295-4753
- Medicare enrollment
- Enrolled (PECOS I20080307000443); accepts Medicare assignment
- Medical or professional school
- Michigan State University College Of Osteopathic Medicine, 1987
- Telehealth
- Offers telehealth (CMS)
- Entity
- Type 1 · individual
8 nearest internal medicine physician records → All 17,696 in California → Look up another NPI →
Also registered at 161 Thunder Dr Ste 210
A shared address usually means a shared clinic or building; it does not show who employs whom.
- Michelle Vanaman, RNFA, CNORRegistered Nurse First Assistant1740413145
Verify Mark C. O'Brien in five checks
- 1IdentityNPI record in CMS NPPESNPI lookupConfirmed in NPPES
- 2LicenseActive license and public ordersMedical Board of California
Search for license 20A6017Check the board - 3Other statesLicenses and actions elsewhereDocInfo (FSMB)Not checked
- 4ExclusionsMedicare and Medicaid bansHHS-OIG exclusion listNot checked
- 5CertificationBoard certificationABMS AOA NCCPA AANPNot checked
95% fewer Medicare Part D claims than the average internal medicine physician in 2024
160 Medicare Part D claims for 93 beneficiaries, against an average of 3,176 among the 108,855 providers of this specialty who prescribed in Part D.
Most prescribed
- Levofloxacin13 claims
- Doxycycline Hyclate12 claims
- Furosemide11 claims
Source: CMS Medicare Part D Prescribers by Provider and Drug, 2024 (data.cms.gov). Part D covers prescriptions for Medicare patients only; drugs with fewer than 11 claims are not published.
Mark C. O'Brien among 17,696 internal medicine physician records in California
Mark C. O'Brien, D.O. is one of 17,696 internal medicine physician records with a practice address in California. 79% of them appear in a Medicare file (Part D prescribing, MIPS, Open Payments or Medicare group billing); this one does. Its NPI, issued in 2005, is newer than 0% of them.
- NPI issued2005 · 0% of these records are older, 95% newer
- In a Medicare fileYes · 79% of these records are
- In the CMS Doctors and Clinicians fileYes · 63% of these records are
- Graduated1987 · median 2004 among the 11,065 with a school on file
- Record last updated2025 · 61% of these records were not updated in five years or more
Source: CMS NPPES, file of Aug 9, 2026, every record with primary taxonomy 207R00000X and a California practice address; Medicare files: CMS Part D Prescribers 2024, MIPS 2023, Open Payments 2024, Doctors and Clinicians (data.cms.gov).
43 internal medicine physician records list a practice address in Vista
They are 43 of the 2,017 NPPES records with a practice address in Vista, and 17,696 internal medicine physician records in California.
All 17,696 in California → Every provider in Vista → Internal Medicine Physician nationwide →
The 8 internal medicine physician records with the nearest ZIP codes
- Emad Abu-Khieran, MDVista, CA 920831558314237
- Kristin Bell, M.D.Vista, CA 920831154335891
- Sanjana Chaturvedi, MDVista, CA 920831881630457
- Farzaneh Hassani, MDVista, CA 920831942204979
- John Lafata, MDVista, CA 920831285662403
- Kiran Mahl-Sansone, M.D., INC.Vista, CA 920831245276815
- Gerald Ondash, MDVista, CA 920831730102153
- Shantu Patel, MDVista, CA 920831851305098
Common questions
What is Mark C. O'Brien, D.O.'s NPI number?
Mark C. O'Brien, D.O.'s National Provider Identifier (NPI) is 1497744247, issued on Oct 14, 2005. An NPI identifies a provider in billing; it is not a license.
Where is Mark C. O'Brien, D.O. located?
The NPPES record lists a practice address at 161 Thunder Dr Ste 210, Vista, CA, 92083. Phone: (760) 216-6500. Providers update this record themselves, so call before visiting.
How can I verify Mark C. O'Brien, D.O.'s license?
NPPES lists California license number 20A6017, as entered by the provider. Search the Medical Board of California at https://www.mbc.ca.gov/License-Verification/default.aspx. The NPPES record confirms identity only; the state search shows license status, expiration and public orders.
How much does Mark C. O'Brien, D.O. prescribe under Medicare Part D?
In 2024, Mark C. O'Brien, D.O. had 160 Medicare Part D claims for 93 beneficiaries; the average among internal medicine physician prescribers was 3,176. Part D covers Medicare prescriptions only.
Source: CMS National Plan and Provider Enumeration System (NPPES), file of Aug 9, 2026 (NPPES files on CMS.gov); NUCC Health Care Provider Taxonomy. Medicare files from data.cms.gov. An NPI identifies who bills; it is not a license.
Figures on PlainDoctor are read from the federal files each page names (CMS NPPES, Medicare Part D, MIPS, Open Payments; the HHS-OIG exclusion list only as counts) and from Census population estimates, with the file date shown beside them. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of Aug 9, 2026.