U.S. health officials are urging doctors to stop using a key antibiotic for routine cases of gonorrhea because of signs of bacterial resistance, leaving only one recommended treatment for one of the most common sexually transmitted diseases in the nation.

The U.S. Centers for Disease Control and Prevention said Thursday it no longer recommends the use of cefixime, an oral antibiotic marketed under the brand name Suprax, because it is becoming less effective. That leaves the injectable generic antibiotic ceftriaxone, used in combination with another antibiotic, as the last treatment option.

Gail Bolan, director of the CDC’s Sexually Transmitted Disease Prevention division, called the change “a critical preemptive strike to preserve the last effective treatment option,” saying it would give time to researchers and drug developers to come up with new treatments.

Until new treatments reach the market, experts say the best way to lessen the risk of drug-resistant gonorrhea is to rapidly diagnose the disease and fight it with combinations of two or more types of antibiotics simultaneously. If left untreated, gonorrhea can lead to pelvic inflammatory disease, ectopic pregnancy, stillbirths,severe eye infections in babies and infertility in men and women.

In the United States, about 300,000 cases of gonorrhea each are reported each year, but because infected people often have no symptoms, the actual number of cases is probably closer to 700,000, Bolan said.

Drug-resistant strains of gonorrhea accounted for almost one in 10 cases of STDs in Europe in 2010, more than double the rate of the year before,health officials from the Stockholm-based European Centre for Disease Prevention and Control said in June.