Legal liability for injuries caused by medical malpractice can be established under a number of legal theories:

Negligence

Most medical malpractice cases proceed under the theory that a medical professional was negligent in treating the patient. To establish medical negligence, an injured patient, the plaintiff, must prove:

• The existence of a duty owed by the health care professional to the plaintiff (for example, a doctor/patient relationship);
• The applicable standard of care, and the health care professional's deviation from that standard, which is deemed a breach of the duty owed the patient;
• A causal relationship between the health care professional's deviation from the standard of care and the patient's injury;
• Injury to the patient.

To find a medical professional negligent, it must be shown that his or her conduct fell below a generally accepted standard of medical care. To establish the standard to be applied, a plaintiff must present the testimony of another medical expert, qualified in the same area of medicine as the defendant, indicating what standard, or level of care, is commonly met by those recognized in the profession as being competent and qualified to practice. The plaintiff will have to present expert testimony not only as to the applicable standard of care, but establishing that the defendant failed to meet this standard.

Negligent Prescription of Medications or Medical Devices

A medical professional may be held liable for the negligent prescription of a medication or medical device if he or she ignored the manufacturer's instructions, or prescribed an incorrect medication or dosage, which resulted in injury to the patient. In some cases, a pharmaceutical manufacturer may be liable where a drug caused a patient injuries, but only if the manufacturer failed to warn of potential side effects or dangers of the drug. In most cases, the prescribing physician is considered a "learned intermediary," which means that because of his or her superior medical knowledge, and the fact that he or she has been given adequate information from the manufacturer, he or she is in the best position to determine whether a particular drug or device is appropriate for a patient. Thus, the physician has the primary duty of advising the patient of the risks and side effects of a medication or medical device he or she prescribes.