Ah, hookworms. We are well acquainted with those nasty things here.
The first time Bootsy got them, we treated him 3 times with panacur before they finally went away. Then put him on Heartgard, which prevents them as well as heartworms. I think it's Heartgard. Then, I accidentally asked the front desk ladies at the vet for a refill of Revolution, which they did (without checking our chart), and that prevents heartworm, but no other worm. So he got them again. He was treated with Drontal - one dose, then another dose 2 weeks later. Seems to have worked, but I need to take in a sample to be sure. He's back on Heartgard.
I would speak with your vet about a preventative in addition to a strong treatment now.
Good luck.