氧四圜素(Oxytetracyclinum)又称土霉素(Terra-mycinum),它是四圜素类的三个抗生素之一。四圜素类的抗生素有氯四圜素(Chlorocyclinum 即金霉素)、氧四圜素及四圜素(Tetracyclinura)。它们的化学构造式如下: Oxytetracyclinum, also known as Terramycotin (Terra-mycinum), which is one of the three antibiotics of the tetracycline class. Tetracycline antibiotics are chlorotetracyclin (Chlorocyclinum chlortetracycline), oxytetracycline and tetracycline (Tetracyclinura). Their chemical structure is as follows: