When developing an oral liquid dosage formulation, consideration is first given to the characteristics of the active drug. The major challenges in developing oral liquid dosage forms are (i) the stability of a drug in solution, (ii) the solubility of a drug at the required level, and (iii) an acceptable taste. It is the effective use of excipients, which allows for-mulators overcome these challenges. Additionally, an excipient’s compatibility with a drug in the solid state cannot infer the same compatibility in solution. However, if the mechanism of degradation of the drug is understood, the process of selecting which excipients to use in a solution will be much easier. Finally, some knowledge of the drug’s physical and chemical characteristics such as the solubility, pH stability, and pKa value(s) of reactive functional groups is essential in order to choose the proper excipients effectively.

Ideally, the pH at which the drug is most stable would also be close enough to the solubility for delivering the desired dose in approximately 5 mL. Requiring patients to take more than 10 mL at a time may not be advisable because of lower patient compliance (variability). In this scenario, a simple oral solution or syrup formulation may be developed. However, if the pH at which the drug is most stable is not one at which there is enough solubility, a suspension formulation may be required.

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