Bioavailability of commercial tetracycline products.

1 Thirteen commercial tetracycline products were assessed for bioavailability by in vitro and in vivo tests. Three failed the B.P. disintegration test and three products in a dissolution test released less than 50% of their stated potency by 3 hours. 2 In vivo bioavailability was assessed by serum and urinary data. Six products were tested by serum data over 48 h and their bioavailability profiles varied but their ranking correlated well with in vitro dissolution in water; three were better than the others. In a further study, based on urinary excretion alone, the thirteen products showed considerable variation in bioavailability. One product gave an extremely poor result (6 mg excreted in 24 hours). 3 These findings of generic non-equivalence illustrate the need for adequate standards of bioavailability testing.