When you decide to end your relationship with a patient, inform him or her in writing and send the letter by certified mail, with a return receipt requested. If it's possible to describe the reason for the termination in a brief, clear, objective way, do so in the letter. If not, you might be better off not providing a reason. The patient ought to be aware of the reason as a result of earlier discussions and correspondence. Some malpractice insurance carriers offer sample termination letters, or you can adapt the following sample.
Dear [patient name],
As you know, a good relationship between a physician and his or her patient is essential for quality medical care. There are times when this relationship is no longer effective and the physician finds it necessary to ask the patient to select another physician.
This letter is to inform you that I am no longer willing to be your primary care physician. The reason for this decision is [describe reason briefly, or omit this sentence]. Our office will continue to direct your care for any emergencies that arise over the next 30 days. It is imperative that you select another physician and arrange with our office for your records to be sent to your new physician before [date]. Your insurance plan or the local medical society [insert contact information] will be able to assist you in choosing a new physician.
Source : medscape.com