In the event of a patient developing an allergic reaction after medication, my immediate priority would be to ensure the patient's safety. First, I would quickly assess the patient's vital signs to determine the severity of the reaction. If the patient is experiencing symptoms such as difficulty breathing, swelling, or a drop in blood pressure, I would immediately call for emergency assistance and alert the medical team. While waiting for help, I would ensure the patient is in a comfortable position, administer oxygen if needed, and prepare to give any emergency medication like epinephrine if it's within my scope of practice. Throughout the process, I would continuously monitor the patient's condition and communicate any changes to the medical team. Additionally, I would document the incident thoroughly, including the patient's response to the intervention, to ensure accurate records and facilitate further treatment decisions.