Chapter 13 Formulation Factors

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Solution Dosage Forms

Drugs are commonly given in solution in cough/cold remedies and in medication for the young and elderly. In most cases absorption from an oral solution is rapid and complete, compared with administration in any other oral dosage form. The rate limiting step is often the rate of gastric emptying. Since absorption will generally be more rapid in the intestine.

When an acidic drug is given in the form of a salt, it may precipitate in the stomach. However, this precipitate is usually finely divided and is readily redissolved and thus causes no special absorption problems. There is the possibility with a poorly water soluble drug such as phenytoin that a well formulation suspension, of finely divided powder, may have a better bioavailability.

Some drugs which are poorly soluble in water may be dissolved in mixed water/alcohol or glycerol solvents. This is particularly useful for compounds with tight crystal structure and higher melting points that are not ionic. The crystal structure is broken by solution in the mixed solvent. An oily emulsion or soft gelatin capsules have been used for some compounds with lower aqueous solubility to produce improved bioavailability.

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