Firstly, there are laws that oblige doctors to indicate other things. For example, we have a law on youth protection, as well as a law on mandatory reporting. In Quebec, under the Health and Social Services Act, there's an obligation to declare all accidents or incidents. They are broader, but they are obligations nonetheless.
Legally speaking, we have, indeed, yet to find a ruling in case law that sanctions a doctor for not having made a report. Why? Because in civil litigation, it must be proven that a doctor made a mistake and that this mistake was harmful to the patient. Yet, when patients consult their doctor because they believe that they are having a bad reaction to a drug, the act of reporting or not reporting this incident—even if that in itself could constitute a breach in civil law—is not the cause of the patient reacting adversely to a drug. Generally speaking, this is not the type of offence that would lead to a malpractice suit. This is why we do not have any case law of this nature.
The only way of making doctors more accountable for their actions is by broadening these obligations through professional ethical codes, or statutory law. Nonetheless, with respect to case law, the courts are not sanctioning this type of offence in civil litigation because the offence in and of itself did not result in the consequences suffered by a patient. It may have consequences on other patients if a report is not made however, there could consequences for other patients. Perhaps other patients who were aware of the fact that a doctor did not declare information that he or she held could take legal action. It is a rather long and arduous road.