Dog heartworm: What slow kill treatment is best with doxycycline?

I am so sorry that Tucker has tested heartworm positive. I adopted a dog that was heartworm positive, so I certainly understand how difficult it is to make a decision on treatment.
I am attaching a link below to the American Heartworm Society (AHS) which has a lot of good information for you.
https://www.heartwormsociety.org/
The AHS does not recommend the "slow kill" method as it's treatment of choice, but does recommend the following for an alternative treatment if needed. They recommend Doxycycline and either ivermectin or topical Moxidextin. ("Topical moxidectin is now FDA-approved for use in
heartworm-positive dogs.") They do not list ivermectin or topical Moxidextin as being better than the other, so they should have the same efficacy. Injectible Moxidectin (Proheart) is not listed by the AHS as recommended and the company that manufactures Proheart lists that it "should be used with caution in heartworm positive dogs".
I am attaching the exact recommendation from the AHS below.
" In cases
where arsenical therapy is not possible or is
contraindicated, the use of a monthly heartworm
preventive along with doxycycline at 10 mg/kg BID
for a 4-week period might be considered. An antigen
test should be performed every 6 months and the
dog not considered cleared until two consecutive
NAD (no antigen detected) heartworm antigen
tests, 6 months apart, have been obtained. If the
dog is still antigen positive after one year, repeat
the doxycycline therapy. Exercise should be rigidly
restricted for the duration of the treatment process."
So, I would recommend reviewing the AHS website, then discussing it further with your vet.
Good luck! I hope that was helpful. Thanks for using PetCoach.