Flea and Tick while treating for HW

My foster dog just started her HW treatment with doxy and pred. Can I apply topical flea and tick like Advantix

Hello.  In this case, I think that HW stands for heartworm? - and you mention heartworm treatment WITH Doxy and Pred.  Because I dont know what the HW treatment is, I dont know whether or not it covers fleas and whether or not it is contraindicated. Furthermore, I prescribed none of these things which makes it ethically dodgy for me to comment.   With drugs that have been prescribed for a particular purpose by a vet, Im afraid that they are the ones who are safe to take responsibility as regards making choices.  Usually they will be happy to speak with you on the subject.