The doctor is only negligent if they knew or had reason to know that the drug was unsafe. If a doctor prescribes a drug and later the Food and Drug Administration (FDA) determines the drug to be dangerous or requires the manufacturer to change the labeling to reflect a newly discovered danger, the doctor will likely not be held liable for your damages.
However, in cases like this, you may have a product liability claim against the manufacturer or distributor of the drug, as those companies are responsible for ensuring their products are safe when used as directed.