Seven healthy male volunteers were administered, on different occasions, one, two, and three capsules of two commercially available brands (A and B) each containing 250 mg tetracycline HCl. Urinary excretion rates and cumulative amounts of drug excreted in the urine in 4 days were used to assess the bioavailability of the two brands at the different doses studied. The rate constants of absorption and elimination of tetracyline were similar at all dose levels. However, the extent of absorption (F)
appears to be dependent on the brand, dose, and volume of water ingested with the drug. F
of Brand B was not significantly different than that of brand A at the 250-mg dose but was decreased by 23.3% (p<>
at the 500-mg dose and by 19.7% (p
0.05) at the 750-mg dose. With respect to dose, F
of each brand at the 500-mg dose was not significantly different than its value at the 250-mg dose. However, F
of brand A at the 750-mg dose was reduced by 14.8% (p
0.05) and that of brand B by 21.1% (p
0.05) relative to their respective values at the single dose. Surprisingly, when the 750-mg dose of brand A was ingested with a small volume of water, F
was increased by 18.9% (p
0.05) compared to the ingestion of the identical dose of the same brand under waterloading conditions.
Key words bioavailability - tetracycline HCl capsules - dose dependency - brand dependency - water ingestion - urinary excretion