The disadvantages are that the dog owner may forget to give the medication and that there are risks of a mild reaction and transient diarrhea if given to a heartworm infected dog. In addition to drug therapy for dogs and cats, mosquito control in residential areas where dogs and cats live can break the transmission cycle of heartworm. Dog owners should keep their animals out of mosquito infested areas. A dog's living quarters should be mosquito-free. Indoor dogs usually show much lower incidence of infection.
Insect repellents are safe and effective when applied properly.