Types of Liquid Dosage Forms

1. Solutions

• The most fundamental liquid form, characterized by the complete and molecular dispersion of the API in a solvent (aqueous, hydroalcoholic, or non-aqueous).

• Offer the fastest onset of action among oral forms as the drug is already solubilized. They ensure maximum dose uniformity since the API cannot settle out.

• Maintaining chemical stability over time due to the constant contact between the API and the solvent (risk of hydrolysis).

2. Syrups

• The concentrated solution in which sucrose is dissolved in purified water. They are sweet in taste and highly viscous. In simple syrups, the sucrose concentration is 66,7% (w/w). They are classified as:

​          - Medicated syrups: Syrups that contain medicament

          - Non-Medicated Syrups: Syrups that are made only for flavoring purpose

3. Elixirs

• The colored, aromatic and hydroalcoholic formulations that are sweet in taste but less viscous.
• Formulated by adding ethyl alcohol, water, flavoring agents, syrups and preservatives.
• Variety of medicated formulations are presentin market which contains very potent therapeutic agents like antibiotic elixirs, antihistaminic elixirs, sedative elixirs.
• Sometime flavoring elixirs are used for flavors as well as vehicles for furtherformulations

4. Drops

• The liquid preparation used for the oral administration. Somevitamins such as vitamin A and vitamin D that are water insoluble but are oil soluble are dispensed in the form of drops for betteradministration.
• During administration, the dose can be accuratelymeasured, hence, commonly used in pediatric formulation.

5. Lotions

• The liquid preparations that are used for topical purposes, applied on the skin without any friction.
• Can be applied with the help of material such as cotton, gauze etc. and applied for the treatment of skin related diseases.
• The medicament used in lotions can be anti-fungal agents likeclotrimazole, Eberconazole, etc. It provides cooling, soothingand protective effect, etc

6. Suspensions 

• The biphasic liquid dosage form in which medicament is finely divided into small solid particles that easily gets dispersedin a liquid vehicle.
• Contains two phases: dispersed phase (solid particles) and continuous phase (vehicle).
• Can be administered through oral or parenteral route as well as usedfor external purposes (Amoxicillin oral suspension, Insulin Zinc suspension).

7. Emulsions

• The biphasic liquid dosage form consisting of two non-miscible liquids (i.e., oil and water).
• Contains two phases: dispersed phase (the liquid is converted into globules minutes) and continuous phase (the liquid into which the globule is dispersed).
• In normal conditions, the immiscible liquids can’t be dispersed for a long time so for the purpose of stability, emulsifying agents are added into the emulsionsystem.
• Emulsifying agent forms a film around the globules so that both the phases can be mixed for a long period of time.

​

Advantages of Liquid Dosage Forms

🔑 A.P.I is homogeneously dispersed in the formulation

🔑 Dose can be adjusted by measuring a specific volume

🔑 Patients having difficulty in swallowing tablets and capsules, can easily swallow solution or syrups e.g., cough syrup.

🔑 Taste of unpleasant drugs can easily be masked by sweeteners and flavoring agents.

🔑 Drugs such as potassium chloride can produce peptic ulcers when administered in the tablet form but prevent this side effect, when administered in liqid form.

🔑 Absorbent compounds and antacids can be easily administered via liqid dosage form

🔑 Some hygroscopic and deliquescent compounds that release water during solid formulations can be easily dispensed through liquid dosage forms.

🔑 The therapeutic response is faster than solid dosage form

Disadvantages of Liquid Dosage Forms

⚠️ Liquid is comparatively difficult during handling and storage

⚠️ The shelf life is less in liquid dosage forms

⚠️ Ingredients are usually more susceptible to degradation

⚠️ Two incompatible components can’t be dispensed together as compared to solid dosage forms.

⚠️ Inconvenient for travelling purposes as there is a problem of spillage

⚠️ Solutions are quickly degraded by microorganisms therefore; preservatives are intended to be added into the formulations

Conclusion

Liquid dosage forms remain indispensable in modern pharmacy, driven by their superior patient acceptance and pharmacokinetic benefits. While their formulation presents challenges related to stability and preservation, ongoing advances in excipient technology continue to enhance the quality and shelf-life of these preparations. Pharmacists and healthcare professionals must accurately classify and understand the specific properties of each liquid form to ensure optimal drug stability, dispensing accuracy, and patient outcomes

Reference

Lokesh Sharma, et. al (2024), "A Review on Liquid Dosage Form", J Pharma Res Rep, 5(1): 1-6