Drug Interaction Report

ADJUST DOSING INTERVAL: Concomitant administration of bismuth-containing medications may impair the absorption of oral tetracyclines. The interaction has been studied with tetracycline and doxycycline. The proposed mechanism is chelation of tetracyclines by bismuth.

MANAGEMENT: Administration of a tetracycline and bismuth-containing preparation should either be avoided or separated by two to three hours. However, this precautionary measure is not considered necessary in treatment regimens where bismuth may be given in combination with tetracycline and other medications for the eradication of Helicobacter pylori infection, as the relative contribution of systemic versus local antimicrobial activity against Helicobacter pylori has not been established.

ADJUST DOSING INTERVAL: Food may impair the gastrointestinal absorption and decrease the bioavailability of bismuth from the administration of bismuth subcitrate potassium (also known as colloidal bismuth subcitrate or tripotassium dicitratobismuthate). The clinical significance of this effect is unknown, as the relative importance of systemic versus local bismuth concentrations for antimicrobial activity against Helicobacter pylori has not been established. Investigators have suggested that the increased gastric retention time of bismuth in the presence of food may be beneficial by prolonging the local exposure of Helicobacter pylori to high concentrations of bismuth, although the amount of bismuth absorbed systemically and secreted back into the gastric fluid may also contribute to its therapeutic effect. When Pylera (a treatment preparation for Helicobacter pylori infection that contains bismuth subcitrate potassium 420 mg, metronidazole 375 mg, and tetracycline 375 mg per recommended dose) was administered after a standardized high-fat breakfast in 23 healthy volunteers, mean systemic exposure (AUC) for bismuth decreased by 60% compared to administration in the fasting state. Metronidazole and tetracycline AUC values were also reduced by 6% and 34%, respectively. However, these changes are not deemed clinically relevant, as eradication rates of Helicobacter pylori near 90% have been reported in trial patients administered Pylera routinely after meals.

MANAGEMENT: Pylera and generic equivalents should be administered after meals (breakfast, lunch, and dinner) and at bedtime (preferably with a snack). The manufacturers for some of the other bismuth subcitrate potassium products have recommended avoiding the ingestion of food, beverages, or other medications within one-half hour before and after each dose. The prescribing information or package labeling should be consulted for dosing and administration instructions that are appropriate for each product.