Nitenpyram is an insecticide used in agriculture and veterinary medicine to kill insect external parasites of livestock and pets.
It is a neonicotinoid, which means that it is a neurotoxin that blocks the ability for neural messages to transmit through the
central nervous system of the flea causing (almost) instant death.

 

Nitenpyram is used orally with dogs and cats to control fleas. After ingestion, it begins killing fleas within 30 minutes and kills all 
adult fleas within 4 hours. The effects of nitenpyram last approximately 24-48 hours. 

Nitenpyram is safe to use on puppies and kittens as young as four weeks old if they weigh at least 2 pounds (0.91 kg). 
Panting and excitement have been noted in cats within 2 hours of administration. In heavily infested animals, it can
cause extreme itching as the fleas die.

Nitenpyram does not kill insect eggs and has no long-term activity. Thus, it is not effective as a long-term flea preventative. 
It is usually used to kill nymph and adult fleas quickly on an infested animal, and combined with a longer term flea 
preventative like fipronil or lufenuron to prevent reinfestation