We use and recommend www.vetcentric.com to order all of your pets' medications.  This is the only veterinary approved website that will honor all manufacturers guarantees. 

For example:  If you purchase a 6 month supply of a heart worm prevention from other web sites and you pet becomes infected with heart worms, there will be no form of financial reimbursement from the company per their guarantee.  If the same medication is purchased from Vetcentric, there can be a monetary compensation. 

There are many prescriptions available on this site along with great people to help you in you have any questions!