I had pinworms for a year before I realized that they were resistant because I was infested with ALOT of other parasites not because they were resistant to the medincine. So strange how the other ones hid so well, despite my constant bombardment with DE. After 8 or so days on albendazole I found I had tapeworms. Oddly, pinworms came back with a vengence while I was on Albendazole! I eventually got the worms undercontrol with DE again (just enough under control that I wasn't suicidal by the itch). And now, finally seem to be getting relief by following ICU's roundworm protocol (with a few unauthorized and maybe poorly laid out modifications... who knows...) And have discovered I also have ascaris. I have no idea how long, I've had it. Since childhood? Recent infection? No idea, did it hide all that time I was doing DE? How about when I was on albendazole? Or did I see them and think they were pinworms? I will never know. Just thinking you might want to consider a heavy roundworm protocol, perhaps other parasites you don't know about are making it impossible to kill the pinworms.