Have Cat Questions? Ask a Cat Vet Online.
The problem with over the counter treatments is that many aren't effective against ‘all' the possibilities. That's why a vet administered med after diagnosis is highly recommended. The vet can determine what kind of parasite (or parasites) your companion has and treat it accordingly with the latest prescription meds and accurate dose. Please see this link http://www.fabcats.org/worming.html
All worms http://www.thepetcenter.com/exa/worms.html