Understanding Pharmaceutical Liquid Dosage Forms

Excipients used in the formulation of liquid dosage forms

Liquid dosage forms are prepared by combining drug substance(s) with different excipients. These excipients serve a variety of function in the liquid formulation; however, several excipients behave differently at different concentration and one excipient can be used for multiple purposes depending upon the need of the dosage form.

When formulating liquid medicines, it is essential to ensure that all the different excipient used is physically and chemically compatible with the drug substance and every other component of the formulation. Below is a list of common excipients generally used in the formulation of liquid dosage forms.

Manufacture of liquid dosage forms

Most liquid dosage forms are prepared:

1. by simply dissolving the solutes (active pharmaceutical ingredient and excipients) in an aqueous or nonaqueous solvent or solvent mixture;
2. by suspending the solutes in appropriate medium;
3. by incorporating the solutes into an oil or water phase.

On an industrial scale, they are prepared in large mixing vessels with ports for mechanical stirrers. The vessels are generally thermostatically controlled to maintain a certain temperature if desired. The order of addition of components is fixed through product development and scale-up exercises.

Packaging of liquid dosage forms

Liquid dosage forms vary widely both physically and chemically, and in the ways they are distributed and used. Consequently, the materials from which the containers and packaging components are made also vary considerably and these containers are usually in direct contact with the formulation. For stability concerns, the container must not physically or chemically interact with the product so as to alter the strength, quality, or purity of the product beyond the official requirements.

Liquid dosage forms that contain light-sensitive active ingredients should be supplied in containers that are light resistant. If the preparation contains volatile ingredients, the liquid preparation should be kept in a tightly closed container. Except where indicated in the individual monograph, containers used in packaging liquid preparations for parenteral and oral use should be made from material that is sufficiently transparent to permit the visual inspection of the contents.

Labelling of liquid dosage forms

Every pharmaceutical preparation must comply with the labelling requirements established under Good Manufacturing Practice. The label should include:

1. The name of the pharmaceutical product

2. The name(s) of the active ingredients; International Nonproprietary Names (INNs) should be used wherever possible

3. The amount of active ingredient in a suitable dose-volume

4. The name and concentration of any antimicrobial preservative and the name of any other excipient

5. The batch (lot) number assigned by the manufacturer;

6. The expiry date and, when required, the date of manufacture;

7. Any special storage conditions or handling precautions that may be necessary

8. Directions for use, warnings, and precautions that may be necessary

9. The name and address of the manufacturer or the person responsible for placing the product on the market.

If the Liquid preparation is supplied as granules or powder to be constituted just before issue for use, the label should include:

1. That the contents of the container are granules or powder for reconstitution
2. The strength as the amount of the active ingredient in a suitable dose-volume of the constituted preparation
3. The directions for preparing the liquid including the nature and quantity of liquid to be used
4. The storage conditions and shelf-life of the constituted preparation.

Quality assurance and quality control/ Evaluation of liquid dosage form

Like any other dosage form, liquid dosage forms have specifications for drug substance and drug products. To ascertain batch to batch uniformity and to ensure stability of the products over the recommended shelf life, manufacturers follow those specifications. An established and validated stability-indicating assay method is the key to quality control/quality assurance. Some of the parameters that are routinely monitored for liquid dosage forms are content uniformity, viscosity, pH, color, and odor. The efficacy of the preservative over the shelf life also should be monitored. For suspensions and emulsions, the effect of storage on flow properties and particle size also should be monitored.

References

• Ansel, H. (2010). Pharmaceutical Calculations, (13th ed.). London: Wolters Kluwer Health and Lippincott Williams & Wilkins.
• Chaudhari, S. and Patil, P. (2012). Pharmaceutical Excipients: A review. International Journal of Advances in Pharmacy, Biology and Chemistry, 1(1): 21-34.
• Denton, P. and Rostron, C (2013). Pharmaceutics: The Science of Medicine Design. United Kingdom: Oxford University Press.
• Gautami, J. (2016). Liquid Dosage Forms. Nano Science & Nano Technology, 10(3):1-9.
• Marriott, J., Wilson, K., Langley, C., and Belcher, D.(2010). Pharmaceutical Compounding and Dispensing (2nd ed.). UK: Pharmaceutical Press.

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