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Our Doctors
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Michael Castro, M.D. FACP

Dr. MICHAEL CASTRO is the founder of Arrowhead Internal Medicine.  He is Board Certified Internal Medicine doctor from the American Board of Internal Medicine since 1997 and is a Fellow of the American College of Physicians. Since 1975, only about 35,000 physicians have earned ACP Fellowship, a mark of distinction representing the pinnacle of integrity, professionalism, and scholarship for those who aspire to pursue careers in Internal Medicine.  

Dr. Castro is the Associate Program Director for the Internal Medicine residency program for Abrazo Arrowhead Hospital/Arizona Heart Hospital.  He’s currently working with internal medicine doctors and students while they finish their training.  He is an associate professor with Midwestern University and the Guadalajara School of Medicine.  He also teaches Nurse Practitioners from ASU, UofA and GCU

As a tribute to his late father, who was a teacher, Dr. Castro is very committed to the education of the next generation of health care providers.  As such, you will see students and trainees of all levels in his office: from Medical Assistants being trained by other MA's to Nurse Practitioners being trained by our other Nurse Practitioners; to medical students and Interns and Residents.  Please be aware that under Dr. Castro's care, you will be seen by several physicians in training supervised by Dr. Castro.  If you are unsure, please let us know and we can arrange your visit with a different provider. 

Dr. Castro served as the Chief of Staff for Abrazo Arrowhead Campus and Abrazo Arizona Heart Hospital from September 2016 until August 2020.  He previously served as the vice-Chief of Staff from September of 2012 to August of 2016.  He also served as the Medicine Department Chairman from September 1999 to 2003 and again from August 2008 to September 2011.  Dr. Castro is a Main Investigator with HOPE Research Institute; he served as a Medical Director for PoPHealthcare and was the Medical Director for the West area for Hospice Inspiris from January 2008 to February 2009.

Dr. Castro graduated from the University of Puerto Rico, Medical Science Campus in 1994.  He finished his residency in 1997 from Maricopa County Hospital in Phoenix AZ. 

Dr. Castro has been recognized as America’s Top Physician for 2008,  2011, 2012, 2013 and again for 2014, 2015 and 2016.  He has been recognized as Top Doc by the  Phoenix Magazine 6 years in a row.


Srivani Srikantiah, MD

Dr. SRIVANI SRIKANTIAH  is board certified in Internal Medicine by the American Board of Internal Medicine since 2001.

She obtained her medical degree from Bangalore Medical College, Bangalore, India and completed her Internal Medicine Residency at the University of Connecticut, Farmington, CT in 2001. Upon graduation from residency, she joined an Internal Medicine Practice in New Haven, CT. She delivered care to both inpatients and outpatients, and was actively involved in teaching Internal Medicine and Family Practice residents and medical students from Yale University School of Medicine during their rotations through her practice.  Dr. Srikantiah has been part of Arrowhead Internal Medicine, PC since February 2011.

She is a member of the American Medical Association.

Erin Tomanek MSN, AGNP-C

Erin is a board certified Adult Gerontology Primary Care Nurse Practitioner. She graduated from Texas Christian University (TCU) with a BSN in nursing in 2011 and worked in the hospital for 10years before continuing her education in advanced practice. She graduated with her MSN from Walden University, and is certified through the AANP. She spent multiple residency hours focused on health in the aging adult. As an AGNP-C she has worked serving the community through mobile medicine doing house calls and through hospice care. Her passion is helping those who cannot help themselves.


In her free time, she enjoys spending time with her husband and two children, exploring Arizona, and volunteering in the community.

Shamina Khan, MMS, PA-C

Shamina Khan, MMS, PA-C, graduated from the Midwestern University Glendale PA program in 2010 and is currently working on her Doctor of Medical Science Program at A. T. Still University.   Shamina practiced as a Family Care Physician in Bombay, India before moving to the US in 2001. During her PA training, she rotated through different clinics, including emergency, urgent care and internal medicine.  She has worked in urgent care and internal medicine for last 10 years.

Shamina is certified in Obesity Medicine through American Board of Obesity Medicine (ABOM) in 2022. She is a Diplomate of American Board of Obesity Medicine.

When not working at the Arrowhead Internal Medicine’s office, Shamina loves to spend time with her family and pets. Shamina is an outdoor person; she loves to hike, and Sedona is her favorite place to do so.  She loves teaching and she is a great preceptor to her medical, PA and high school students.

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