Effect of omeprazole on Helicobacter pylori urease activity in vivo

Detection of Helicobacter pylori infection in clinical routine is based either on the direct visualization of the bacterium in gastric biopsies by histology or microbiology or on the demonstration of urease activity in gastric biopsies and by the labelled-urea breath test (UBT). Omeprazole has a strong inhibitory effect on H. pylori urease activity in vitro, but its effect in vivo and thus its influence on urease-based diagnostic procedures has not been investigated systematically.

To investigate whether omeprazole is able to inhibit H. pylori urease activity in vivo and, if so, at which doses.

Eighteen patients with H. pylori associated chronic gastritis were studied.

H pylori diagnosis was based on histology, rapid urease test and culture from antral biopsies. Following a positive H. pylori diagnosis patients received omeprazole 20mg (n = 6), 40mg (n = 6) and 80mg (n = 6) once daily for 5 days and 13C-UBT was performed on day 1, 3 and 5, 30min after each omeprazole administration. The 13C-UBT was performed with 200ml 0.1 N citric acid as test drink and 75mg 13C-urea. Breath samples were collected before and 30 min after 13C-urea administration.

A significant inhibition of urease activity was observed only under high dose omeprazole administration (80 mg/day), and the 13C-UBT turned negative in three (50%) of these patients after 5 days therapy.

Short-term omeprazole administration reduces H. pylori urease activity only at doses as high as 80 mg/day. A direct inhibition of enzyme activity as well as a reduction in the number of viable H. pylori bacteria may be responsible for this omeprazole-mediated reduction in urease activity. Urease-based diagnostic procedures for H. pylori are not suitable for patients under omeprazole therapy depending on the dose and duration of therapy.