How Safe Is Doxycycline In Treating Heartworms In Dogs? Vet Wants To Treat For One Year With Little To No Activity In That One Year. My Dog Is At Stage 2, Treated For One Year, No Sign Of "Baby" Heartworms.

Doxycycline use in treatment of heartworm is new and not main stream at this point.  Doxycycline is not the main core of the treatment and from protocols I've read is used more short term.  This is still controversial and up for debate among the cardiologists.   I do not think the research is there to switch from protocols that work.  There is one abstract about this slow kill method using Doxycycline but much of the date may have been extrapolated and the method not tested.
 It is still recommended to use an injectable medication called Immiticide.  Other treatment modalities used in conjunction with Immiticide are prednisone, and Heartguard.
Please talk to your veterinarian about your concerns.  A second opinion is also something you can get from another veterinarian in your area.