How old is the kitten? You only used one tube/application, right? On the back of it's neck? Has it been licking it off?
Cats can be poisoned in a number of ways. Cats can directly ingest a toxic substance either by eating it or by eating poisoned prey. They can also swallow poisons while grooming contaminated fur. Some toxins can even be absorbed through the skin of the cat, (particularly the paws), and a few can gain entry by inhalation.
The clinical signs are very variable and will depending on the particular poison concerned. Many toxins produce gastrointestinal signs (vomiting and diarrhoea), others produce neurological signs (tremors, incoordination, seizures, excitability, depression, or coma), respiratory signs (coughing, sneezing, difficulty breathing), skin signs (inflammation, swelling), liver failure (jaundice, vomiting) or kidney failure (increased drinking, inappetence and weight loss). Some toxins act on more than one body system, and so can produce any combination of the above signs. It is important to remember that while most cases of intoxication will cause acute problems, chronic intoxication can also arise, and often proves even more difficult to recognise and treat.
If you do think that it has been poisoned, you need to get it to a vet asap!