Ilaria Oliver Mastroserio, PA-C
NPI 1376197590ActiveIndividual· Physician Assistant· Walnut Creek, CA
Physician Assistant (PA-C) with John Muir Physician Network, practicing in Walnut Creek, California. Their prescriptions cost Medicare Part D more than their services did: $780,159 for 309 claims, against $38,150 paid for services in 2024. Merck Sharp & Dohme LLC was the largest of 21 companies reporting payments in 2025, $1,189 in all, mostly food and beverage. Lists John Muir Medical Center - Concord Campus and 1 other hospital as hospital affiliations.
Overview
| NPI | 1376197590 |
|---|---|
| Status | Active |
| Entity type | Individual |
| Credential | PA-C |
| Sole proprietor | No |
| NPI issued | Jul 25, 2019 |
| Last updated in NPPES | May 22, 2024 |
| Certified by provider | May 22, 2024 |
Specialties and licenses
| Taxonomy | Code | License | State |
|---|---|---|---|
| Physician Assistant Primary | 363A00000X | — | — |
Exclusion screening
| List | Result | Details |
|---|---|---|
| HHS-OIG LEIE · Nov 10, 2026 | No match | Checked by NPI and by name + state |
| North Carolina Medicaid · Nov 11, 2026 | No match | — |
| New York OMIG · Nov 11, 2026 | No match | — |
| Ohio Medicaid · Nov 11, 2026 | No match | — |
| Pennsylvania Medicheck · Nov 11, 2026 | No match | — |
| Washington HCA · Nov 11, 2026 | No match | — |
Official OIG search · How matching works ·Bulk check a roster
Medicare
| Enrollment (PECOS) | Enrolled Practitioner - Physician Assistant (CA) |
|---|---|
| Accepts assignment | Yes (participating) |
Medicare services in 2024
| Medicare patients | 203 |
|---|---|
| Services billed | 420 across 14 procedure codes |
| Paid by Medicare | $38,150 |
Part D prescriptions in 2024
| Prescriptions (claims) | 309 · 375 30-day fills |
|---|---|
| Patients | 131 |
| Total drug cost | $780,159 |
| Generic share | 83% of claims |
Education and affiliations
| Graduation year | 2019 |
|---|---|
| Medicare specialty | Physician Assistant |
| Telehealth | Offers telehealth |
Medical group
- John Muir Physician NetworkPleasant Hill, CA · 494 clinicians
Hospital affiliations
- John Muir Medical Center - Concord CampusConcord, CA
- John Muir Medical Center - Walnut Creek CampusWalnut Creek, CA
Industry payments (Open Payments)
- 2025$1,189 · 44 payments from 21 companies
- 2024$216.38 · 9 payments from 7 companies
Top paying companies in 2025
| Company | Amount | Payments |
|---|---|---|
| Merck Sharp & Dohme LLC | $151.60 | 6 |
| Astrazeneca Pharmaceuticals LP | $143.43 | 5 |
| Adaptive Biotechnologies Corporation | $137.40 | 1 |
| Novartis Pharmaceuticals Corporation | $101.24 | 4 |
| Celgene Corporation | $81.75 | 3 |
What the 2025 payments were for
- Food and Beverage$1,189 · 44 payments
Receiving payments does not imply wrongdoing. What Open Payments covers ·original records
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All 95 physician assistants in Walnut Creek · All physician assistants in California