Flevox, flea shampoo and Frontline reaction?

Our customer asked:

I applied a cheap dog flea treatment after finding a flea on my dog on Monday. He has had this before but this time it doesnt seem to have worked.
I have bought Vetzyme insecticidal Dog shampoo which I intend to use today followed by Flexox but want to know how long I should wait from shampooing to using the Flexox as I dont want to make my dog ill? Also after using frontline on my cat she seems to have developed scabs at the base of her hair although her coat looks ok and a nervous thing and wont come in the house .Do you think this may be a side effect of the front line?

Our reply:

Now that you have spotted a flea, it is very likely that there are high numbers of other fleas, developing from eggs, larvae and pupae in nooks and crannies around your house. A small proportion of these will probably jump onto your dog and cat every day. If suitable treatment has been applied, they will die off over a day or two, but they will still be able to bite you pets in that time.

It sounds as if your cat has "milliary dermatitis" which is often called "flea allergy". The scabs you have noticed are probably her reactions to flea saliva injected under the skin when a flea bites. Hence this is a reaction to fleas, not to the treatment, which you should continue with.

You should allow 48 hours between shampoo and spot-on applications. You would be well advised to treat your house for fleas, with a product like Indorex. You will be able to get the fleas under control, but some will be around for a while and it is very difficult to get rid of all of them in less than a month or two.