Proton pump inhibitors (PPIs) act only in the stomach, although the proton pump, H+,K+-ATPase exists and contributes to H+ and K+ homeostasis in the kidney. We encountered two hypokalemic cases receiving omeprazole. These cases were women ages 69 and 80 years old. Their serum potassium levels decreased with accelerated urinary potassium excretion with the use of omeprazole, and recovered by potassium-supplement and the discontinuation of omeprazole. Because inhibitory effects of PPIs on H+,K+-ATPase are exerted only in acidic condition, hypokalemia is not generally introduced by PPIs alone. However, in extreme alkalosis or impaired K+-recycling system, PPIs may cause hypokalemia unrelated to hypomagnesemia.
