BURROUGHS WELLCOME'S ANTIDOTE TO DIGOXIN INTOXICATION, DIGIBIND,

BURROUGHS WELLCOME'S ANTIDOTE TO DIGOXIN INTOXICATION, DIGIBIND, will be available to hospitals and poison control centers by the summer, the firm announced following approval of the drug May 8. Digibind (digoxin immune FAB (ovine)), approved as an orphan drug, is indicated "for treatment of potentially life-threatening digoxin intoxication," labeling states. Burroughs Wellcome said the drug "is expected to meet an immediate life-saving need in the estimated 10,000-20,000 patients per year who experience severe, and often irreversible, digoxin and digitoxin intoxication." Digibind labeling notes that "although designed specifically to treat life-threatening digoxin overdose [Digibind] has also been used successfully to treat life-threatening digitoxin overdose." The labeling adds that "since human experience is limited and the consequences of repeated exposures are unknown, Digibind is not indicated for milder cases of digitalis toxicity." According to the labeling, "manifestations of life-threatening toxicity include severe ventricular arrhythmias such as ventricular tachycardia or ventricular fibrillation, or progressive bradyarrhythmias such as severe sinus bradycardia or second or third degree heart block not responsive to atropine." Burroughs Wellcome said it hopes to eventually broaden the indication for Digibind to include serious toxicity. The company markets digoxin under the brand names Lanoxin and Lanoxicaps. A product license application for the biologic was submitted to FDA in August 1984. The drug, supplied in vials of 40 mg of purified lyophilized digoxin-specific Fab (antigen binding fragments), costs $150 per vial. Labeling states that "the dosage of Digibind varies according to the amount of digoxin to be neutralized. The average dose used during clinical testing was 10 vials." The labeling further notes that "if a patient presents with digitalis toxicity from an acute ingestion, and neither a serum digitalis concentration nor an estimated ingestion amount is available, 20 vials (800 mg) of Digibind can be administered. This amount will be adequate to treat most life-threatening ingestions in both adults and children." Burroughs Wellcome explained in its release that Digibind is made of "purified fragments of digoxin specific antibodies. To obtain the antibody, sheep (ovine) are injected with digoxin linked to serum albumin so that the digoxin will cause antibody formation." The company said the digoxin antibody "is fragmented so that the only portions of the molecule that remain are those needed to bind to the circulating digitalis" which makes "the possibility of allergic reaction less likely." Labeling warns that "although no allergic responses have yet occurred in man, the sample size is small and one should therefore consider the possibility of anaphylactic, hypersensitivity or febrile reactions." With regard to adverse reactions, the labeling states: "In a few instances, low cardiac output states and congestive heart failure could have been exacerbated by withdrawal of the inotropic effects of digitalis. Hypokalemia may occur from re-activation of (sodium, potassium) ATPase. Patients with atrial fibrillation may develop a rapid ventricular response from withdrawal of the effects of digitalis on the atrioventricular node." FDA noted in a press release announcing the approval that digoxin use is involved in about 175 deaths from accidental overdose and suicide each year. "In addition, thousands of the 4 mil. patients on digoxin each year may require treatment for digitalis intoxication with severe heart arrhythmias or heart block," the agency stated. FDA said Digibind "is the first biological product that is a specific antidote to a drug." Burroughs Wellcome will distribute Digibind and its parent, Wellcome Foundation, will manufacture the drug.