Biological Availability of Digoxin from Lanoxin Produced in the United Kingdom

Though established quality control standards were maintained, the bioavailability of digoxin from Lanoxin tablets produced in the United Kingdom fell in 1969, and was restored in 1972. After 1·5 mg doses of representative batches, tablets made between 1969 and 1972 produced mean values for area under the 50 hours plasma concentration/time curve of 36·6 ng/ml/hr and four-day urinary excretion of 340 μg, compared with respective values of 67·5 ng/ml/hr and 696 μg for recently produced tablets. After 0·5 mg doses of four recent independently produced batches of Lanoxin tablets no significant between-batch difference was found for area under the plasma concentration/time curve or cumulative urinary excretion. Absorption of digoxin from batches of Lanoxin manufactured since May 1972 is uniform and consistent. Content uniformity is an inadequate measure of tablet quality, and consistent digoxin bioavailability cannot be ensured by existing regulations.