The U.S. Food and Drug Administration has approved a new drug raxibacumab for inhalational anthrax, the agency announced on Friday.

Inhalational anthrax is an infectious disease caused by breathing in the spores of the bacterium Bacillus anthracis. FDA said that the current drugs used to treat the infection weren't adequate.

Raxibacumab is a monoclonal antibody, FDA said in a statement, which neutralizes toxins produced by B. anthracis. These toxins can cause tissue damage and death.

For the first time, the agency has approved a monoclonal antibody to treat an infection under the FDA's Animal Efficacy Rule. A monoclonal antibody is a protein that resembles a human antibody that identifies and neutralizes foreign bodies like bacteria and viruses.

The approval came after controlled studies were conducted on animals. This is because anthrax is a rare, lethal disease and it is not possible to conduct drug trials on human test subjects.

"In addition to antibiotics, raxibacumab will be a useful treatment to have available should an anthrax bioterrorism event occur. Although antibiotics are approved to prevent and treat anthrax infection, raxibacumab is the first approved agent that acts by neutralizing the toxins produced by B. anthracis," said Edward Cox, director of the Office of Antimicrobial Products in FDA's Center for Drug Evaluation and Research in a statement.

The effectiveness of the drug Raxibacumab was established after a study on monkeys and three studies on rabbits. The test subjects received aerosolized B. anthracis spores. These animals were then given varying doses of the drug, a placebo or antibiotics normally used to treat anthrax.

Studies showed that more animals treated with raxibacumab survived after being exposed to B. anthracis spores than placebo.

In addition, safety of the drug was tested in 326 healthy human volunteers. Side effects of the drug included rash, itching pain and drowsiness, the agency said

The drug was developed by GlaxoSmithKline PLC's Human Genome Sciences, Associated Press reported.