100mg is correct, however unstable vtach c a pulse synch. cardioversion is the treatment of choice, also you give O.5 to 0.75mg per kg if your pt has a pulse as loading dose. If the pt is in cardiac arrest (vt, no pulse) it is 1 to 1.5mg per kg.
The other option is amio 150mg in d5w over 10 min with a pulse or 300mg without.