Frustrated with a changing health care system that has resulted in longer workdays and less time with patients, a growing number of doctors in California and across the nation are turning to a new type of practice – concierge medicine. The model is simple: Doctors charge their patients an annual fee and in turn give them more time and attention. Critics say it fosters two-tiered medicine where patients who cannot afford the extra fee are cut off from their doctors. The practice raise ethical concerns that warrant careful attention, particularly if retainer practices become so widespread as to threaten access to care, according to a recent report in the San Francisco Chronicle.