There are now a wide variety of drugs available that are able profoundly to
reduce the production of gastric acid. These drugs are currently widely pr
escribed for the treatment of peptic ulceration and gastro-oesophageal refl
ux disease. One of the main functions of gastric acid is to kill ingested b
acteria. Colonization of the gastric lumen occurs in patients on antisecret
ory medication, the degree of bacterial overgrowth depending upon the degre
e of elevation of the pH. There have been concerns that these bacteria may
produce carcinogenic nitrosamines and increase the risk of gastric cancer,
but there is at present no definitive evidence in support of this. A profou
nd suppression of gastric acid may also facilitate the colonization of the
upper small intestine, leading to deconjugation of the bile salts and malab
sorption. There is some evidence that profound gastric acid suppression may
decrease the number of ingested pathogens required to produce enteric dise
ase. This chapter discusses these potential bacterial complications of ther
apeutic acid suppression and the evidence for them.