Significant differences were found in the absorption characteristics of three commercial tetracycline preparations. These differences were observed after both single‐dose and multiple‐dose administration. The relative amount of tetracycline absorbed (biological availability) but not the relative rate of absorption was greater for a standard preparation than for two other similar preparations. These differences provide a means to evaluate general methods to assess differences in the biologic availability of tetracycline products. It was e0tablished that the pharmacokinetic parameters obtained from single‐dose urinary excretion studies would reflect the differences observed in the areas under the serum curve of single‐dose studies and the mean serum concentrations in multiple‐dose studies. It is suggested that single‐dose studies with urine collections for 48 to 72 hours are adequate to assess differences between brands of tetracycline, evaluate formulation and physiologic variables affecting biologic. Vailability, and develop correlations with in vitro dissolution rates. From these results on a very small sample of commercial preparations, it is considered possible that there may be sufficient differences between products which, in some clinical situations, may result in therapeutic failures.
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Barr et al. (1972) studied this question.