Journal of Antimicrobial Chemotherapy, Vol 39, 5-12, Copyright © 1997 by The British Society for Antimicrobial Chemotherapy
PO Erah, AF Goddard, DA Barrett, PN Shaw and RC Spiller
Although omeprazole is an important component in anti-Helicobacter pylori
therapeutic regimes using clarithromycin, amoxycillin and metronidazole,
the mechanism by which it enhances antimicrobial action is unknown. One
potential explanation for this effect is increased antibiotic chemical
stability resulting from gastric pH changes induced by co-administration of
omeprazole. The chemical stability of clarithromycin, amoxycillin and
metronidazole was investigated in aqueous solutions and in human gastric
juice collected before and after a 7-day course of omeprazole. Amoxycillin,
clarithromycin and metronidazole were prepared in buffered aqueous
solutions of pH 1.0 to 8.0 and in gastric juice of pH 2.0 and 7.0. The
gastric juice samples were obtained from fasted H. pylori-negative
volunteers before and after they had received a 7-day course of omeprazole.
All the samples were incubated at 37 degrees C and analysed at intervals by
HPLC. Amoxycillin, clarithromycin and metronidazole were stable in aqueous
solutions of pH 4.0-7.0, pH 5.0-8.0 and pH 2.0-7.0, respectively. At pH
2.0, the degradation half-lives were 19.0 +/- 0.2 h, 1.3 +/- 0.05 h and
2200 +/- 1100 h, respectively. In gastric juice samples of pH 2.0, the
degradation half-lives were 15.2 +/- 0.3 h, 1.0 +/- 0.04 h and > or =
800 h, respectively. The half-lives of the drugs in the gastric juice
samples of pH 7.0 were all > 68 h. The co-administration of omeprazole
with amoxycillin or clarithromycin is likely to increase the chemical
stability of amoxycillin and clarithromycin in gastric juice.
Clarithromycin degrades rapidly at normal gastric pH (1.0-2.0) but
amoxycillin and metronidazole are sufficiently stable at this pH to
maintain an antibacterial concentration in the stomach.
JOURNAL ARTICLE
The stability of amoxycillin, clarithromycin and metronidazole in gastric juice: relevance to the treatment of Helicobacter pylori infection
Department of Pharmaceutical Sciences, University of Nottingham, University Park, UK.
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