The Food and Drug Administration (FDA) announced approval of pyridostigmine bromide to increase survival after exposure to Soman "nerve gas" poisoning. The product is approved for combat use by United States military personnel.

Pyridostigmine bromide is the first drug approved under a recently issued FDA rule (frequently referred to as the "animal efficacy rule") that allows use of animal data for evidence of the drug's effectiveness for certain conditions when the drug cannot be ethically or feasibly tested in humans.

The "animal efficacy rule," which became effective on June 30, 2002, is an important component of FDA's efforts to make medical countermeasures available to treat or prevent the effects of biological and chemical agents.

FDA Commissioner Mark B. McClellan, M.D., Ph.D., said, "Today's action will help protect American troops and others from nerve agent attacks."

The "animal efficacy rule" enabled FDA to approve pyridostigmine bromide to increase survival from Soman poisoning despite the impossibility of ethically conducting human studies on the effectiveness of the drug.

The nerve agent Soman causes loss of muscle control and death from respiratory failure. Evidence of the effectiveness of pyridostigmine bromide as a pretreatment for exposure to Soman was obtained primarily from studies in monkeys and guinea pigs. This evidence shows that administration of the drug before exposure to Soman, together with atropine and pralidoxime given after exposure, increases survival. FDA believes that, based on the animal evidence of effectiveness, pyridostigmine bromide is likely to benefit humans exposed to Soman.

The agency's safety assessment is based on long-term use of pyridostigmine bromide, first approved by FDA in 1955, to treat a neuromuscular disease called myasthenia gravis. The Department of the Army has submitted data from multiple controlled trials and uncontrolled clinical experience demonstrating pyridostigmine bromide is well-tolerated at the doses intended for military use. The dose used for myasthenia gravis is higher than the dose used for pretreatment to protect against Soman.

To use this potentially lifesaving drug correctly, military personnel must carefully follow instructions and use the drug only under specific circumstances. For example, if U.S. troops faced the threat of exposure to Soman, they would be given instructions to take pyridostigmine bromide every 8 hours prior to the anticipated exposure. Soldiers will be warned that the drug is not effective and should not be taken at the time of, or after exposure to Soman.

The troops are to use the drug in conjunction with other protective measures, including chemical protective masks and battle dress garments. Furthermore, effectiveness depends on the rapid use of the antidotes atropine and pralidoxime and discontinuation of pyridostigmine bromide at the first indication of nerve gas exposure. The Department of Defense plans to provide all military personnel with extensive training, prior to deployment, on the proper use of pyridostigmine bromide, as well as other methods used in the prevention and treatment of nerve agent poisoning.

A leaflet that explains the drug's use, benefits, and side effects will be provided to military personnel when the drug is distributed. The leaflet advises that pyridostigmine bromide should not be used by persons who have a history of bowel or bladder obstruction, or sensitivity to certain medicines used during surgery (like physostigmine). Side effects that may occur include stomach cramps, diarrhea, nausea, frequent urination, headaches, dizziness, shortness of breath, worsening of peptic ulcer, blurred vision, and watery eyes.

The approved dose of pyridostigmine bromide for Soman pretreatment is one 30-mg. tablet every 8 hours. The leaflet states that pyridostigmine should be started at least several hours before exposure to Soman and emphasizes that it must be discontinued upon exposure to nerve gas, at which point the antidotes atropine and pralidoxime are given.

During the Gulf War, FDA had allowed distribution of pyridostigmine bromide under its Investigational New Drug provisions because pretreatment with this drug had the potential to help save lives if nerve agents were used.