In vivo pH effects

The sensitivity of the properties of most dmgs to changes in the pH of their environment 

Effects are not always clear-cut, as pointed out at the beginning of this chapter. There are contradictory reports of the effect of antacids on the absorption of levodopa, as one example. Levodopa is metabolised within the gastrointestinal tract and more rapidly degraded in the stomach than in the intestine, so the rate at which the dmg is emptied from the stomach can affect its availability. It has been suggested 

The use of cimetidine, ranitidine, nizatidine, famotidine and other H2-antagonists has given rise to the possibility of a dmg interaction involving the increase in gastric pH, as these dmgs inhibit gastric acid secretion (see Fig. 9.7 in section 9.1.3). A few subjects have transient achlorhydria after oral cimetidine, so increased absorption of acid-labile dmgs is a predictable side-effect, as breakdown is reduced. 

Sodium bicarbonate (sodium hydrogen carbonate) is one of the most effective antacids in terms of neutralising capacity. It can greatly 

Antacid Neutralising capacity of Dose required to Weight of tablet No. of 

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