https://www.google.com/amp/s/pix11.c...dications/amp/
There are side effects to all flea preventatives. For Nextgard, make sure you read that article.
I recommend Revolution because it stops eggs from hatching whereas Frontline stops the larvae from growing. Revolution is a better choice for an already established infestation.
Vacuum, vacuum, vacuum, especially the rugs and carpets. Toss the pet beds out just to be safe. Use your flea comb as much as you can.
Flea bombs might not work because eggs can survive them.
Treat all rooms but try to keep the pets from moving from room to room too much.
Lastly, after the fleas are gone, you will need to check for tapeworms. Fleas carry these suckers as a host which passes on to dogs and cats.