Our Providers

Vera Becka

Vera Becka, M.D.


Dr. Becka was born and raised in Germany where she completed her medical training and met her American husband. She started her pediatric residency in Germany and moved to the U.S. in 2004, where she re-did her pediatric residency at The Children’s Hospital in Denver. She loves taking care of her patients’ immediate healthcare needs as well as preventive care, teaching, and supporting chronically ill patients and their families.

Dr. Becka joined Horizon Pediatrics in August 2010, and thoroughly enjoys establishing relationships with her patients and their families and hopefully making a difference in their lives. In her free time she loves spending time with her husband, her two children, traveling, hiking, and enjoying the great outdoors.

Joe Williams

Joe Williams, M.D.


Dr. Williams earned his medical degree from the University of Tennessee and was inducted into Alpha Omega Alpha, the medical school honor society. He also holds a Phd in physiology from West Virginia University. Pediatrics has always been his passion and he enjoys working with children experiencing ADHD, allergy and asthma, obesity and other childhood challenges.

Dr. Williams was born in South Carolina, but raised in Georgia so he’ll always be a bit of a country boy. The joy of practicing pediatrics surrounded by the beauty of Colorado was a lifestyle he could not resist, so he settled here in 1993 and plans to stay forever. He is an avid fly fisherman and enjoy all outdoor activities. Gardening is another one of his passions and he considers himself to be a master at grilling.

“I look forward to meeting your children and designing measures to guide them through a healthy childhood”Joe Williams

Dr. Ackerman

Donna Ackerman, DO


Dr. Ackerman earned her Osteopathic medical degree from The College of Osteopathic Medicine of the Pacific, in Pomona, CA. She went on to do a rotating internship followed by her Pediatric Residency at Loma Linda University Hospital in California. There, she was asked to stay on for a 4th year Chief Residency. Dr. Ackerman came to beautiful Colorado right after residency and had a private group practice for over 22 years before joining with Horizon Pediatrics.

Dr. Ackerman was raised in South Dakota until she was thirteen, when her Pediatrician father joined the Air Force and the family moved to Southern California. She completed high school there and obtained a BS in Biology from California State University, San Bernardino before starting medical school. Although she misses the ocean, she has loved Colorado as a healthy active place to raise her three boys. They all ski and hike and love to camp, enjoying the outdoor life. She also enjoys the large art community activities and the downtown theatre offerings.

“ My  goals are to work together with parents to raise healthy intuitive children, and for kids in my clinic to understand healthy living for a lifetime.”


Janina Czartolomna, MD

Internal Medicine

Dr. Czartolomna is a licensed Internal Medicine Provider who has been practicing in the Thornton area for over 20 years. She spent 13 years as a pulmonologist in Poland before relocating to the U.S.. She completed her residency in Internal Medicine at Presbyterian St. Luke’s Medical Center.

She believes that a preventative lifestyle is an important foundation for overall health. In her spare time, she enjoys travelling and hiking at remote locations (off the beaten path).


Mark Flanigan, MD

Family Medicine

Dr. Flanigan is a Colorado native who received his medical degree from St. Louis University, and is a certified Family Medicine provider. He has been practicing for over 35 years, of which 27 have been in Thornton.

In his spare time, he enjoys spending time with his grandchildren, hiking and playing tennis.


Meggan Macias picture

Meggan Macias, PA-C


Meggan Macias is a Physician Assistant with an expertise in pediatrics and adolescent medicine. She was a 2002 graduate of the Child Health Associate/Physician Assistant program at the University of Colorado Health Sciences Center. She has practiced primary pediatrics for the past ten years and has additional training in adolescent gynecology, behavioral medicine and newborn feeding issues.

Meggan and her husband, Gene, have three children together—twins, Geno and Isabel, and a younger son, Dallas. They live in Parker, CO and enjoy traveling, all types of music and sports activities with their children.

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Emily Wilson, PA-C

Family Practice & Woman’s Health

Emily Wilson, is a graduate of Arcadia University’s Physician Assistant program. She has been board certified since 2009 and has been practicing in Colorado since that time. She has a particular interest in Adolescent Women’s Health and contraception.

Prior to PA school Emily was a student athletic trainer for the University of Colorado and acted as the primary healthcare provider for all campers and counselors at an all girls sleep-away camp in Vermont.

In her free time, Emily enjoys spending time camping, rafting, and enjoying the Colorado outdoors.


Sara Flanigan, PA-C

Family Practice

Sara Flanigan is a Colorado native, who graduated Valedictorian of her class from Arcadia University. She has been a practicing Physician’s Assistant in Thornton for the past 5 years. Sara enjoys family medicine and working with both children and adults, and gets to know the entire family.

She has two young children of her own, so even though she really enjoys practicing yoga, hiking and being outdoors, she spends most of her time with her family and their dog.


Whitney Harrington, PA-C


Whitney was born and raised in Oklahoma where she graduated summa cum laude from the University of Oklahoma with a Bachelor’s degree in Psychology and minor in Spanish.  She then went on to earn her Masters in Physician Assistant Studies from the University of Colorado’s CHA/PA Program in 2010.  Soon after graduation she moved to Idaho where she practiced as a Pediatric PA from 2010-2013.

Whitney joined Horizon Pediatrics in 2014 and enjoys building relationships with families in the greater Denver area.  Her interests include adolescent medicine, asthma and allergy, and childhood obesity/nutrition.  Whitney also speaks Spanish and is eager to serve the Latino community.

Whitney is a member of both the American Academy of Physician Assistants and American Academy of Pediatrics.  In her free time she enjoys spending time with family and exploring the great outdoors while hiking, biking, backpacking, skiing and traveling.


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Tony Oakes, PA-C


Tony earned his Physician Assistant certification in 1998 at the University of Colorado Health Sciences Center. He received his Bachelor’s degree in Kinesiology from the University of Colorado at Boulder.

Prior to his work at Horizon pediatrics, Tony was a physician assistant for eight years at Child First Pediatrics, where he provided extensive healthcare to children. He also practiced family medicine at the Inner City Health Center for two years as well as pediatrics at Aspen Family Care for 5 years in Highlands Ranch. Tony enjoys all aspects of pediatrics, particularly adolescent and behavioral medicine.

Tony is actively involved at his church, where he also volunteers regularly. He enjoys and competes regularly in trail ultramarathons. Tony resides in Castle Rock where he passionately loves his two children, Benjamin and Gracie.


John Laukkanen, LCSW

Developmental & Behavioral Health

John is a Licensed Clinical Social Worker (LCSW) with a Master’s degree in Religion as well as a Master’s in Social Work. He has worked with children and families in settings such as school classrooms, foster care placements, and church ministry.

His role as a Behavioral Health Consultant (BHC) is to support those struggling with social, emotional, or behavioral challenges. His primary focus is to provide brief interventions, education, and coaching around these challenges. John is certified as a Perinatal Mood Specialist (pregnancy-related mood concerns). He can also help identify and connect families with community-based resources as needed.

“I am able to meet with you either in conjunction with your scheduled medical visit or as a separately scheduled appointment. I look forward to meeting you and supporting your family as a member of the Horizon team!”


Erika Guider, PA-C


Erika Guider, PA-C received her undergraduate degree in Molecular Biology and Microbiology from the University of Central Florida in 2006. Upon receiving her Master of Medical Science degree in Physician Assistant Studies from Nova Southeastern University in 2011, she began her medical career as a Physician Assistant. In addition to being a Certified Physician Assistant, Erika is also BLS certified by the American Heart Association and is a Certified Surgical Technologist.

Erika joined IMMUNOe in July of 2018 and enjoys seeing patients of any age for dermatological services, treatments, and procedures at our Thornton and Green Valley Ranch offices.