In the context of treating an infant with severe symptomatic bradycardia that does not respond to airway management and ventilation, the first drug that should be administered is epinephrine. This medication is essential because it plays a crucial role in stimulating the heart and increasing heart rate. In cases of bradycardia, particularly when symptomatic and not resolved through initial lifesaving measures, epinephrine acts as a potent vasopressor and cardiac stimulant, helping to improve perfusion and cardiac output.
While other medications like atropine can also be indicated in cases of bradycardia, especially in older children or specific scenarios, epinephrine is the preferred first-line choice for infants due to its rapid action in emergency situations. Adenylic acid, while relevant in cardiac pharmacology, is not utilized in this specific scenario. Similarly, while calcium can be important for various cardiac conditions, it is not the immediate first-line treatment for symptomatic bradycardia. Therefore, administering epinephrine is aligned with current pediatric advanced life support guidelines, emphasizing its critical role in managing life-threatening bradycardia in an infant setting.