To the Editor.—
Concerning the interaction of antibiotics with other drugs (219:206, 1972), Kabins is correct in stating that gastrointestinal binding of tetracycline with polyvalent cations (aluminum, calcium, and magnesium) may decrease the absorption of the antibiotic.It is of interest that the absorption of tetracycline has recently been shown to be decreased by concurrent therapy with antacids in the absence of chelation.1 In this instance, depressed blood levels of tetracycline were noted when the antibiotic was administered with sodium bicarbonate. Patients receiving 250-mg capsules of tetracycline and 2.0 gm of sodium bicarbonate concomitantly were compared to patients receiving tetracycline alone. Approximately a 50% decrease in absorption (as reflected by urinary tetracycline excretion) was seen for the patients given the tetracycline-sodium bicarbonate regimen. The results of this study indicate that higher pH environments (above 3) decrease the dissolution rate of tetracycline capsules and lead to lower plasma levels.
Tatro DS. Tetracycline-Antacid Interactions. JAMA. 1972;220(4):586. doi:10.1001/jama.1972.03200040098028
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