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Radioprotective Drugs Approved by FDA

Cheryl A. Thompson

A pair of drugs to decrease internal exposure to radioactive materials after a terrorist attack was approved Wednesday by the Food and Drug Administration (FDA).

The approvals of injectable pentetate calcium trisodium (PDF) and pentetate zinc trisodium (PDF) came about four months after German manufacturer Hameln Pharmaceuticals GmBH submitted its paperwork and nearly a year after FDA published drafts of the products' labeling and invited applications to market the drugs in the United States. FDA took the aggressive actions as part of its efforts to promote the availability of countermeasures to terrorist attacks, including the detonation of a radiation dispersal device, also known as a "dirty bomb."

Pentetate is short for diethylenetriaminepentaacetate, or DTPA, which, according to the FDA-approved labeling, will trade a calcium or zinc ion for a plutonium, americium, or curium ion to form a stable chelate. The radioactive chelate is then excreted in the urine. If treatment starts early enough, damage from radiation exposure, including bone marrow suppression, may be averted.

Both products' labeling state that pentetate calcium trisodium, if available, should be administered instead of pentetate zinc trisodium during the first 24 hours after known or suspected internal contamination with plutonium, americium, or curium. After the initial 24 hours, the two products have roughly the same effectiveness.

The recommended initial dose of pentetate calcium trisodium in persons age 12 years or older is 1 g by intravenous (i.v.) injection. In children younger than age 12, the initial dose is an i.v. injection of 14 mg per kilogram of body weight but not more than 1 g total. Patients with renal impairment may need hemodialysis to speed up removal of the radioactive chelate.

If, on the second day and thereafter, more treatment is needed to remove the radiation, the products' labeling recommend that pentetate zinc trisodium be given because it has less-severe adverse effects than the calcium formulation. The recommended daily maintenance dose of pentetate zinc trisodium is the same as the initial dose of pentetate calcium trisodium.

Despite the inclusion of "injection" in both products' official names, the drug solutions may be administered by a nebulizer if the patient's sole exposure to the radiation was by breathing it in. The products' labeling state that the safety and effectiveness of the inhalation route of administration in children have not been established.

The most commonly reported adverse effects from injection with pentetate calcium trisodium were headache, lightheadedness, chest pain, an allergic reaction, dermatitis, metallic taste, nausea, diarrhea, and an injection-site reaction. Information about the adverse effects from pentetate zinc trisodium therapy was less specific, but the drug does not deplete zinc and other essential nutritional metals like the calcium formulation does.

Pentetate calcium trisodium and pentetate zinc trisodium will be manufactured in glass ampuls containing 200 mg/mL of drug in 5 mL of solution, 10 ampuls per package.

The German manufacturer said Friday that it is working on a plan to market the two drug products in the United States.