Anti-anthrax Agent Shows Promise in Humans

NEW YORK (Reuters Health) - A human monoclonal antibody against the agent that causes anthrax (Bacillus anthracis protective antigen), which has shown action against inhaled anthrax in animals, appears to be safe and well tolerated in humans as well, researchers report.

"This report describes the first investigational agent against anthrax infection to be evaluated in a clinical study since the 2001 anthrax attacks in the United States," Dr. Mani Subramanian of Human Genome Sciences in Rockville, Maryland and colleagues write in Clinical Infectious Diseases, a medical journal.

With further successful testing, the anti-anthrax agent dubbed "PAmAb" could be used in individuals with suspected or probable exposure to aerosolized anthrax spores.

Anthrax spores lend themselves well to aerosolization are hard to breakdown in the environment; "thus they represent one of the greatest threats in biological warfare," the scientists note.

Following a single dose, PAmAb provided complete protection against death in a rat model of anthrax disease. It also provided a survival advantage in rabbits and monkeys.

This led Subramanian's team to investigate PAmAb's safety and activity in 105 healthy human volunteers. Subjects received a variety of doses of the agent or placebo as a continuous infusion or a single intramuscular injection.

Results showed that PAmAb can be safely administered in humans and is well tolerated, producing only transient mild-to-moderate side effects, according to the team.

Moreover, the agent has a long half-life in the human body after a single injection and, importantly, provides serum levels that have been shown to provide protection against anthrax in animals.

These findings, the researchers conclude, support "further clinical development of PAmAb as a novel therapeutic agent for inhalational anthrax."

SOURCE: Clinical Infectious Disease July 1, 2005.