From acne to sore eyes. Doxycyline is said to be a great cure and is also being studied for a cure for Covid 19. Tetracycline is used to treat infections caused by bacteria including pneumonia and other respiratory tract infections; certain infections of skin, eye, lymphatic, intestinal, genital and urinary systems; and certain other infections that are spread by ticks, lice, mites, and infected animals. Doxycycline is a broad-spectrum antibiotic synthetically derived from oxytetracycline Label. This drug is a second-generation tetracycline, exhibiting lesser toxicity than first-generation tetracyclines 7. Doxycycline may be used to treat a wide range of bacterial infections, depending on the results of antibiotic susceptibility testing.