A patient is in refractory ventricular fibrillation and has received multiple appropriate defibrillation shocks, epinephrine 1 mg IV twice, and an initial dose of 300 mg amiodarone IV. The patient is intubated. A second dose of amiodarone is now called for. The recommended second dose of amiodarone is what?

a) 150 mg
b) 300 mg
c) 450 mg
d) 600 mg