Final answer:
Epinephrine is the first drug to be administered when ventricular fibrillation is refractory to the second defibrillation attempt during a cardiac arrest.
Step-by-step explanation:
When a patient is in cardiac arrest and ventricular fibrillation (Vfib) has been refractory to a second shock, the first-line drug that should be administered is epinephrine. In a medical setting, after the initial defibrillation attempts, if ventricular fibrillation persists, epinephrine is recommended by the Advanced Cardiac Life Support (ACLS) guidelines to increase the likelihood of a successful resuscitation. This is important to establish a normal sinus rhythm, which is critical for patient survival.