LIQUID DOSAGE FORM

The use of liquid pharmaceuticals has been justified on the basis of ease of administration and rapid and efficient absorption of the drug. Dosage forms meant either for internal, external or parenteral use may be sub-classified into monophasic or biphasic liquid dosage forms.

The classification of the liquid dosage form is given in Fig 1 and the comparison of characteristics of various liquid dosage forms is shown in Table 1

Fig.1 Classification of liquid dosage form

Monophasic liquid dosage forms for oral use

This class of monophasic liquid dosage form comprises one phase pourable pharmaceutical formulations intended for oral use.

 Examples include mixtures, linctuses, draughts, elixirs, syrups, and drops.

Biphasic Liquid Dosage Form

Biphasic Liquid Dosage Form Contain two Phases. This includes undissolved drug And the solvent System(Vehicle).

Examples: Suspension and Emulsion. 

Table 1. Comparison of characteristics of various liquid dosage forms

Advantages of Liquid Dosage Forms

The presentation of drugs as liquid dosage form offers the following advantages:

1. The drug is more readily available for absorption from liquid dosage forms as compared to the solid dosage form. By providing the drug in solution, the dissolution phase of the absorption process can be surpassed, providing a faster therapeutic response.
2. The doses of drugs can be easily adjusted according to the need of the patient. 3.Liquids are easier to swallow than tablets or capsules and are therefore especially suitable for children, the elderly, intensive care, and psychiatric patients.
3. Gastric irritation due to certain drugs like potassium chloride and when administered as a solid dosage form is avoided or reduced on administration as a liquid dosage form because of the immediate dilution by gastric content.
4. Drugs with large doses can be easily administered as the liquid dosage form.
5. The distribution of a drug in liquid dosage forms is better than solid dosage forms.
6. Liquid dosage forms are more economical to produce than solid dosage forms.
7. Liquid dosage forms can be designed to administer via a number of routes. Parenteral preparations, douches for vaginal use, cutaneous (for use on skin) preparations, and ophthalmic preparations can all be liquids.

Disadvantages of Liquid Dosage Forms

There are also some disadvantages associated with the use of liquid preparations:

1. Drugs are usually less stable in liquid dosage forms as compared to solid dosage forms like tablets and capsules, particularly if they are susceptible to hydrolysis,
2. Liquids, especially aqueous preparations, are susceptible to microbial contamination.
3. Masking the unpleasant taste of a drug in solution is more difficult than when the drug is in a solid dosage form.
4. Liquid preparations are usually bulky and therefore inconvenient to store and carry. Liquid dosage forms are always much larger and more bulky than solid formulations. Coupled with this is the fact that pharmaceutical liquids are packed in glass bottles, which are prone to breakage.
5. Administration of the correct dose is less precise since it depends on the ability of the patient to measure the correct dose using a suitable measuring device such as a spoon or a dropper.
6. The measuring device is to be supplied to the patients for accurate dose administration. This will have cost implications and in addition, counseling is required for its use.
7. Suspensions and emulsions have the added drawback that they must be thorough.

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