Hey Graham & Kersey ~

Dad found this on the Interceptor site...

"INTERCEPTOR Flavor Tabs must be administered monthly, preferably on the same date each month. The first dose should be administered within one month of the dog's first exposure to mosquitoes and monthly thereafter until the end of the mosquito season.

If a dose is missed and a 30-day interval between dosing is exceeded, administer INTERCEPTOR Flavor Tabs immediately and resume the monthly dosing schedule."

Above taken from:
Interceptor Site (http://www.petwellness.com/dog_inter_disc.asp)

Interceptor has an 800# where you can talk to a specialist (I *think* she said "Doctor" when I called) - it's 888-327-9745.

She said missing ONE dose - *IF* the dogs have been on Interceptor for at least 6 months prior, and CONTINUE to receive it at 30 day intervals, will probably not be a problem. She advised contacting you Vet to discuss the situation.
She also advised that you will have to wait 6 months before a heartworm TEST will be worthwhile.

Sounds like the FurKids are not in great danger.