Development of cimetidine resistance in the Zollinger-Ellison syndrome.

A patient with the Zollinger-Ellison syndrome was followed with multiple gastric secretion tests and serum gastrin analyses for six years. During this period cimetidine requirement increased to a daily dose of 8 g, but it reversed spontaneously after two years. The altered cimetidine effectiveness was not associated with reduced oral bioavailability and serum calcium was unchanged. Total serum gastrin was very high at all times, and fractionation of gastrins in serum by gel filtration showed varying proportion of big to small gastrins, but not in a mode which explained the parietal cell resistance to cimetidine.