At least 6 weeks. You can start to worm your kitten at 4-5 weeks of age, but it’s good to give the medication over a couple of days to be sure that they have been completely infected with tapeworm eggs and adult worms. At this point you should also check for fleas as well – adult fleas can survive off an infected host for 15 days or more!
How does deworming work?
There are two main types of worming drugs: ones which kill all parasites in the body (whereas other types only target particular parasites) and those which prevent the larvae from hatching out into adults. It is important that any immuno-suppressant worming medication given by mouth kills all stages of parasite life cycles as otherwise the immune system will become compromised due to repeated exposure to different infectious agents. In addition, avoid using antiparasitic medications on kittens under 1 month old as their immune systems do not yet fully mature and could be overwhelmed by these strong medicines.