Effect of surfactant on tetracycline absorption across everted rat intestine.

Absorption of tetracycline hydrochloride (500 micrograms/ml) from oxygenated modified Krebs buffer in randomized everted rat jejunal segments was determined alone and in the presence of calcium, polysorbate 80, and calcium plus polysorbate 80. Surfactant increased absorption of tetracycline in the presence and absence of calcium, with 0.01% (w/v) polysorbate 80 increasing transfer to the greatest extent of the concentrations examined(0.005, 0.01, 0.05, 0.1, and 1%); tetracycline hydrochloride + 12.5 mM CaCl2, 143 +/- 45 micrograms/ml; tetracycline hydrochloride + polysorbate 80, 389 +/- 18 micrograms/ml; tetracycline hydrochloride + 12.5 mM CaCl2 + polysorbate 80, 255 +/- 31 micrograms/ml. On the premise that the effective surfactant concentration is similar to the critical micelle concentration, an absorption mechanism based on micellar solubilization is postulated.