Terramycin (Oxytetracycline Hydrochloride and Polymyxin B Sulfate Ophthalmic Ointment) is an antibiotic, bright yellow in color, possessing potent antimicrobial activity. It is one of the most versatile of the broad-spectrum antibiotics, and is effective in the treatment of infections due to gram-positive and gram-negative bacteria, both aerobic and anaerobic, spirochetes, rickettsiae, and certain of the larger viruses. Polymyxin B sulfate is one of a group of related antibiotics derived from Bacillus polymyxa. The polymyxins are rapidly bactericidal, this action being exclusively against gram-negative bacteria. The broad-spectrum effectiveness of Terramycin against both gram-positive and gram-negative organisms is enhanced by the particular effectiveness of polymyxin B against infections associated with gram-negative organisms, especially those due to Pseudomonas aeruginosa, where polymyxin B is the antibiotic of choice. In addition, there is evidence to indicate that polymyxin B sulfate possesses some antifungal activity. The combined antibacterial effect of Terramycin plus polymyxin is at least additive and, in many instances, an actual synergistic action is obtained. Terramycin is an ointment of oxytetracycline hydrochloride and polymyxin B sulfate in a special petrolatum base. Each gram of ointment contains oxytetracycline HCl equivalent to 5 mg of oxytetracycline and 10,000 units of polymyxin B as the sulfate.