Physicians and Staff

The physicians, nurses, technicians and administrative personnel at the Gastroenterology Clinic of San Antonio are dedicated to providing the highest quality medical services and care available.

Our medical team is comprised of some of South Texas’ most capable and knowledgeable physicians. Along with the rest of our staff, they pledge to do all they can to alleviate your stress and uncertainty while making your experience with us as comfortable and as effective as possible in addressing your medical needs.

In addition to general gastrointestinaI study, our physicians have special interests and training in Irritable Bowel Syndrome, Inflammatory Bowel Disease, novel endoscopic surgical techniques, motility, non-cardiac chest pain and esophageal disorders, capsule endoscopy, and endoscopic ultrasound.If you have questions or concerns at any time during the course of your treatment, please do not hesitate to contact us. We will be more than happy to assist you.

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  Gary S. Gossen, M.D.

  Learn more about Dr. Gossen at DrGossen.com

  Dr. Gossen has joined Gastroenterology Clinic of San Antonio. He is an assistant clinical professor of internal medicine at the UT Health Science Center at San Antonio. He is currently the medical director of the San Antonio Endoscopy Center and a member of Gastroenterology Research of San Antonio. Read more…
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  Allison H. Sirakos, M.D.

  Dr. Sirakos completed her medical degree at the University of Texas Southwestern Medical Center in Dallas, Texas. She completed her internal medicine residency at New York University and came back to Texas to finish her gastroenterology fellowship at the University of Texas Health Science Center at San Antonio.

  Read more…
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  Russell Dean Havranek, M.D.

  Learn more about Dr. Havranek at RussellHavranekMD.com

  Currently in private practice, Dr. Havranek serves as an assistant professor at the University of Texas Health Science Center in San Antonio. He also completed his residency in internal medicine, an assistant professorship in the liver transplant program and a fellowship in gastroenterology at the Health Science Center. Read more…
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  Nicholas Martinez, MD

  A native of San Antonio, Dr. Martinez is a graduate of Baylor University and attended medical school at the University of Texas Health Science Center at San Antonio. Dr. Martinez completed his internal medicine residency and gastroenterology fellowship at the Health Science Center. His specialty interest includes: inflammatory bowel disease, gastroesophageal reflux disease and colon cancer prevention. Read more…
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  Bassem W. Mazloum, M.D.

  Learn more about Dr. Mazloum at DrMazloum.com

  Dr. Mazloum graduated from The American University of Beirut, Lebanon, in 1987. In 1990, he completed his internal medicine residency training at St. Vincent Hospital in Worcester, Massachusetts, and served as chief medical resident in the same institution until 1991. Dr. Mazloum then completed a fellowship training in gastroenterology from 1991-1995 at The University of Texas Health Science Center at San Antonio and has been in practice since 1995. Read more…
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  Charles W. Randall, M.D.

  Charles W. Randall, M.D., is the medical director of Clinical Research for the Gastroenterology Clinic of San Antonio. His specialty interests include esophageal disorders, functional bowel syndrome, therapeutic endoscopy, new endoscopy techniques and inflammatory bowel disease. Read more…
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  John A. Vizuete, M.D., MPH

  Dr. Vizuete completed his undergraduate training at the University of Texas at Austin. He obtained his medical degree from the University of Texas Health Science Center in San Antonio in 2012. He also holds a master’s degree in public health from the University of Texas School of Public Health in Houston. Dr. Vizuete completed Internal Medicine residency and Gastroenterology fellowship at UTHSCSA where he was named the Chief GI fellow. He joined the Gastroenterology Clinic of San Antonio in 2018.
  Read more…
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  V. Franz Zurita, M.D.

  Dr. Zurita has been in private practice in Texas since 1999 in both San Antonio and the McAllen area and has served on the medical faculty of the University of Texas Health Science Center as assistant clinical professor. Read more…