EFFECT OF INTRAGASTRIC PH ON THE ABSORPTION OF ORAL ZINC ACETATE AND ZINC-OXIDE IN YOUNG HEALTHY-VOLUNTEERS

Background: Zinc is an important nutrient and is necessary to maintain a multitude of physiologic processes. Mineral supplements that provid e physiologic doses of zinc may be used when dietary zinc is inadequat e. Zinc is also used in pharmacologic doses to treat zinc deficiency a nd diseases such as Wilson's disease and acrodermatitis enteropathica. Although there are several zinc salts available, they are not equal i n solubility, which is thought to be a key factor in zinc absorption. Moreover, the solubility of the salts is affected by pH, which may var y between pH 1 and 7 under various physiologic conditions in the stoma ch. The objectives of this 2-way 4-phase crossover study were to evalu ate the effect of high (greater than or equal to 5) and low (less than or equal to 3) intragastric pH on the absorption of zinc from the ace tate and oxide salt in young healthy volunteers. Methods: After a g-ho ur fast, 10 healthy subjects (5 males and 5 females) were given a sing le oral dose of 50 mg of elemental zinc as the acetate or the oxide sa lt and under either high or low intragastric pH conditions. In all pha ses, a Heidelberg capsule pH detector-transmitter was used to continuo usly monitor intragastric pH. During the high pH phases, single oral d oses of famotidine 40 mg oral suspension were administered before the zinc to raise the intragastric pH above 5. Intragastric pH less than o r equal to 3 was maintained in the low pH phases. Results: The mean pl asma zinc area under the curve for zinc acetate at low pH (AL), zinc a cetate at high pH (AH), zinc oxide at low pH (OL), and zinc oxide at h igh pH (OH) were 524, 378, 364, and 66 mu g x h/dL, respectively. The highest zinc plasma concentrations occurred with the acetate salt at a low intragastric pH, while the lowest plasma concentrations occurred with the oxide salt at a high intragastric pH. The importance of pH to the dissolution of these salts was verified by in vitro tests. Twenty -four-hour urinary zinc excretion was the highest for the AL phase and lowest for the OH phase. Conclusion: This study indicates that intrag astric pH and salt solubility-dissolution are important in the oral ab sorption of zinc. Specifically the oxide salt is not an appropriate zi nc salt to use in those patients with elevated intragastric pH.