Biological availability and in vitro release from oral oxytetracycline and tetracycline preparations.

Abstract: The in vitro dissolution rates of 7 oxytetracycline and 2 tetracycline preparations and the absorption characteristics as obtained by a randomized, cross-over study on 10 healthy volunteers, were studied. It was found that a. Two oxytetracycline preparations (nos. 1 and 7) were inferior to the others in terms of mean serum levels and in producing non-detectable or insufficient serum concentrations in 2 and 3 persons respectively. b. The bio-availability of the 5 other oxytetracycline preparations were of the same order (statistically not significantly different) although one preparation (no. 3) exhibited higher mean serum levels, c. The area under the serum concentration curves were proportional to and correlated with the amounts of oxytetracycline and tetracycline recovered in the urine during the period of study, d. The rate of dissolution was related to the absorption characteristics cfr. the preparations 1 and 3. No correlation could be demonstrated between the results of the dissolution tests and the results of the absorption study for preparation 7. e. The tetracycline preparations gave serum concentrations above those of mast oxytetracyclines. f. The oxytetracycline and tetracycline preparations tested showed marked variation in the biological availability of active ingredients.