The reese's pinworm med is an over the counter medicine. Its main ingredient is pyrantel pamoate which paralyses most bigger parasites, like flukes and roundworms. It has to be followed by a laxative so they are flushed out before they wake up. Not sure in which country you are but try to find pyrantel pamoate. Otherwise you can find the reese's version on ebay or amazon. They also make the horse paste which is the same thing but it contains more pyrantel.
You need to cleanse for months and months. If you stop too soon, they immediately return.