Effervescent formulation excipients

Effervescents comprise a soluble organic acid and an alkali metal carbonate salt. Citric acid is most commonly used for its flavor-enhancing properties. Malic acid imparts a smoother after taste and fumaric, ascorbic, adipic, and tartaric acids are less commonly used [14], Sodium bicarbonate is the most common alkali, but potassium bicarbonate can be used if sodium levels are a potential issue with the formulation. Both sodium and potassium carbonate can also be employed. Other excipients include water-soluble binders such as dextrose or lactose, and binder levels are kept to a minimum to avoid retardation of disintegration. All ingredients must be anhydrous to prevent the components within the formulation reacting with each other during storage. 

Excipients such as mannitol can affect small intestinal transit, which in turn can affect the absorption of certain drugs. Oral solutions are rarely likely to fall short of bioequivalence relative to solid oral formulations, although during the development of a ranitidine effervescent oral solution dosage form containing sodium acid pyrophosphate (SAPP), a marked decrease in absorption was observed in the extent of ranitidine absorption from the liquid formulation relative to the conventional oral tablet. The formulation contained 150 mg ranitidine with 1132 mg SAPP together with 1.5 MBq hndium chloride solutions. Small intestinal transit time was decreased to 56% in the presence of the excipient. The rapid small intestinal transit associated with an excipient of a solution dosage form resulted in a decreased extent of ranitidine absorption. " ... 

As an excipient, potassium bicarbonate is generally used in formulations as a source of carbon dioxide in effervescent preparations, at concentrations of 25-50% w/w. It is of particular use in formulations where sodium bicarbonate is unsuitable, for example, when the presence of sodium ions in a formulation needs to be limited or is undesirable. Potassium bicarbonate is often formulated with citric acid or tartaric acid in effervescent tablets or granules on contact with water, carbon dioxide is released through chemical reaction, and the product disintegrates. On occasion, the presence of potassium bicarbonate alone may be sufficient in tablet formulations, as reaction with gastric acid can be sufficient to cause effervescence and product disintegration. 

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