DeWorm Extra Strength is a broad spectrum anti-worm medication, used for the treatment of threadworm, hookworm, whipworm, and roundworm infestations. 

Mebendazole both 100mg and 500mg are on the WHO essential medicines for children so both are safe to use and are being used to treat worm infestations.

With global immigration into New Zealand from Asia, Africa and the Pacific Islands their diet is very different in the way they prepare their meals and are susceptible to hookworm, whipworm and roundworm. Perfect for those travelling to these regions and for those coming from these regions.

So if treating only threadworm then the 100mg strength will be sufficient.

If treating the other worms as well the 500mg strength will be needed.