Most of them work on the adult worms, but may not be completely effective on the developing worms, which is why you may have to give another dose of deworming medications several weeks after the first dose. (vetinfo.com)
Free - roaming cats and dogs may need to be periodically treated with deworming medication. (brittonroadveterinaryclinic.com)
Once the initial infection is treated properly it is a good idea to occasionally check a stool sample for the presence of worms or to consider prophylactically administering deworming medications if the situation seems to warrant it (outdoor cats, for instance). (vetinfo.com)