I have recommended the retention mebendazole enema as many who had pinworm infestations have managed to sleep with it without itching like hell at night.
If you are so sick from taking pyrantel I would look into the possibility of being infected with roundworms as they are common too. The actual side effects are not the med itself but the parasite toxins released that are being hit by the med. So it is a sign of a bad infestation. Pyrantel should be taken weekly at least for a while, roundworms take a year at least to clear up. Usually more or many infections coexist together and it takes years for symptoms to appear.