By Toni Clarke

WASHINGTON (Reuters) - Dr. Margaret Hamburg, who as commissioner of the U.S. Food and Drug Administration (FDA) for almost six years has overseen public health initiatives ranging from tobacco control and food safety to personalized medicine and drug approvals, is stepping down, the agency said on Thursday.

Hamburg, 59, is one of the longest-serving FDA commissioners in the modern era. She was nominated by President Barack Obama and confirmed by the U.S. Senate in May 2009 and last year was named the world's 51st most powerful woman by Forbes magazine.

In a note to staff, Hamburg said it was "with very mixed emotions" that she planned to step down at the end of March and that her tenure as FDA chief "has been the most rewarding of my career."

Dr. Stephen Ostroff, the FDA's chief scientist, will fill Hamburg's position until a new commissioner is named.

Late last month, the agency named Dr. Robert Califf, a prominent cardiologist and researcher from Duke University, to oversee its drug, medical device and tobacco policy. Califf is viewed by many as a potential successor to Hamburg.

A long-time public health official with extensive experience fighting AIDS and tuberculosis, Hamburg, who graduated from Harvard Medical School, previously served at the National Institutes of Health before becoming New York City's health commissioner. That public health focus endeared her to patient advocates.

"Commissioner Hamburg, from day one, has been committed to being a champion for patients," said Ellen Sigal, founder and chair of Friends of Cancer Research. "She has fostered the growth of science and innovation across the agency and really changed how FDA and industry collaborate."

Hamburg's resignation comes as the FDA prepares for what could be a significant transformation, spurred on the one hand by initiatives in Congress to speed new drug development, and on the other by food safety advocates, backed by the president, who would like to see the creation of a separate agency combining the food safety functions of the FDA and the U.S. Department of Agriculture.



Under Hamburg's leadership the FDA, which oversees products representing more than 20 cents of every dollar spent by U.S. consumers, has proposed measures to improve nutrition by limiting dangerous trans-fats in food and requiring restaurants to post calorie counts on menus. It also has beefed up inspections of food and drugs from overseas and increased patient engagement in the drug development process.

The agency has introduced multiple measures to speed the development and review of new drugs. In 2014, the FDA approved 51 new therapies, the most in almost 20 years. In a blog post on Wednesday, Hamburg called the achievement "a testament ... to FDA's innovative approaches to help expedite development and review of medical products that target unmet medical needs."

During her tenure the FDA has confronted major public health issues, including the rise of antibiotic-resistant bacteria, the abuse of opioid painkillers, the emergence of electronic cigarettes and the outbreak of Ebola and other infectious diseases.

Her ride has not always been smooth. She faced hostile questioning by Republicans in Congress following a fungal meningitis outbreak in 2012 that killed dozens of people and sickened hundreds more. She also has been caught up in some controversial political battles.

In 2011, then Health and Human Services Secretary Kathleen Sebelius overruled the FDA's decision to allow an emergency contraceptive known as Plan B to be sold over the counter to young teenagers. Hamburg insisted Plan B was safe for use and it was approved two years later.

The health department's current secretary, Sylvia Burwell, said in a statement that Hamburg "leaves a legacy of incredible, historic accomplishment at FDA."

Hamburg was never a crusading commissioner in the way of one of her predecessors, Dr. David Kessler, who fought to bring tobacco under FDA regulation. But she has made her mark on multiple issues, including the use of targeted therapy to tailor medicines to an individual's genetic makeup. The FDA gained regulatory authority over tobacco products for the first time on her watch, in 2009.

Hamburg comes from a distinguished medical family. Her mother was the first African-American woman to attend Vassar College and to earn a degree from Yale University School of Medicine.


(Editing by Ian Geoghegan, Bill Trott and Meredith Mazzilli)