Lansoprazole and ranitidine affect the accuracy of the 14C-urea breath test by a pH-dependent mechanism.

To determine the effect of lansoprazole and high dose ranitidine on the accuracy of the 14C-urea breath test (UBT). Using intragastric pH recordings, we correlated the effect of these agents on the UBT with their potency of gastric acid suppression.Patients with active Helicobacter pylori infection underwent a baseline UBT before receiving 14 days of lansoprazole (30 mg/day) or ranitidine (300 mg b.i.d.). During therapy, patients were asked to undergo 24-h intragastric pH monitoring. Repeat breath testing was performed 1 day after completion of the study drugs. If the UBT was equivocal or negative (14CO2 excretion was < 200 dpm), further UBTs were completed until the 14CO2 excretion was > 200 dpm.Thirteen patients received lansoprazole. Eight of thirteen patients developed a negative or equivocal UBT. All patients had 14CO2 excretion > 200 dpm 5 days after the cessation of lansoprazole. Eleven patients received ranitidine. Ranitidine led to equivocal or false negative UBTs in 2 of 11 cases. This effect resolved within 5 days of stopping ranitidine. Intragastric pH recordings revealed that the patients who experienced the most profound gastric acid suppression were those that developed equivocal or false negative UBTs.Lansoprazole significantly affected the accuracy of the UBT, causing equivocal or false negative results in 61%. High dose ranitidine affected the breath test in only 18%. The ability of these drugs to suppress gastric acid secretion predicted those patients who developed equivocal or false-negative UBTs. The effect on the accuracy of the UBT resolved within 5 days of drug cessation.