There is no record of any adverse reaction between Program
Plus and Comfortis, but every dog is different. My advice is not to give
another medicine with Comfortis. Don’t give any medication for 2 weeks. Spinosad (the active ingredient for Comfortis) has been
shown to be a substrate for P-glycoprotein (PgP). Spinosad could therefore
interact with other PgP-substrates (for example, digoxin and doxorubicin) and
possibly enhance adverse reactions from such molecules or compromise efficacy
My advice is to treat your pet and your house and yard at the
same time. Repeat the treatment of your house after 2 weeks.