Influence of omeprazole on bioavailability of bismuth following administration of a triple capsule of bismuth biskalcitrate, metronidazole, and tetracycline

The objective of this study was to determine the impact of omeprazole on bismuth (Bi) bioavailability when given in a three-in-one capsule containing bismuth biskalcitrate, metronidazole, and tetracycline. Thirty-four healthy volunteers were randomly assigned to receive three capsules (each containing bismuth biskalcitrate 140 mg + metronidazole 125 mg + tetracycline 125 mg) qid alone x 6 days or the same treatment + omeprazole (OM) 20 mg bid. Blood was drawn at intervals for 24 hours after the last close. After the last dose, mean (CV) C-min for plasma bismuth was 2882 pg/mL (36%) and 1195 pg/mL (23%) (p < 0.001), with and without OM, respectively. Mean (CV) C-max was 25,493 pg/mL (69%) and 8061 pg/mL (28%) (p < 0.001) with and without OM, respectively. AUC(0-24) increased by 2.9 in presence of OM (p < 0.001). Adverse events in both groups were usually mild and of a gastrointestinal nature, and all had resolved by the end of the trial. This study confirms an interaction between Bi biskalcitrate and OM. Risk of Bi toxicity, seen after long-term use of Bi compounds, is minimal here because plasma levels of Bi remained well below the toxic levels of 50 mug/L, and the treatment period with this triple capsule + OM is only 10 days, a substantially lower number of days compared to that which might produce Bi toxicity.