Safeguard and toxic worm overload?

[brettzim]

Is it okay to worm my hens for the first time with fenbendazole? I know they have worms because I have found roundworms in their poop. I do not want to create a toxic worm overload however. I have fendendazole and wazine both on-hand but I've read it's recommended to worm with Valbazen first and then repeat in ten days with fenbendazole to prevent all the worms for dying at once and harming/killing the chicken.