Doryx is an antibiotic used in the treatment of bacterial infections such as Rocky Mountain spotted fever, and other fevers that are caused by sexually transmitted infections, fleas, ticks, lice, eye infection, and respiratory tract infections. Doryx works only against bacteria; it has no effect on viral infections.Doryx (doxycyclinehyclate) is an antibacterial medicine. Doryx is used to treat a broad range of bacterial infections. It works by killing the bacteria causing infection and slowing their growth and reproduction. By slowing the growth of bacteria, it gives the body time to boost its immunity to fight the infection. In many cases, Doryx can be used a malaria vaccine for travelers planning to visit a malaria-infected area for less than four months. It can also be used to reduce the progression of anthrax in an infected patient. Doryx can also be combined with other drugs to treat acne condition. The drug is supplied in the form of capsules and should be administered orally. Avoid this drug if you have stomach infections or diarrhea.