Dosage Forms I (PT303): Liquid Forms

Study Notes

Course offered by the Faculty of Pharmacy, Department of Pharmaceutics & Industrial Pharmacy, Suez Canal University
Intended for second-year pharmacy students, academic year 2021/2022

Understanding solution properties, solubility factors, and dissolution is crucial for pharmaceutical formulations.
Solvents are generally present in larger amounts; however, exceptions exist. (e.g., Syrup BP contains 66.7% w/w sucrose in 33.3% w/w water).
Advantages:
- Easy to swallow for paediatric and geriatric patients.
- Rapid drug absorption, faster therapeutic response.
- Homogenous drug distribution.
- Reduced irritation to gastric mucosa compared to solid dosage forms.
Disadvantages:
- Bulkier and less convenient to store and transport.
- Often less stable compared to solid dosage forms.
- Potential for microbial growth, requiring preservatives.
- Difficulty in precise dosage without a measuring device.
- Often more noticeable taste than solid dosage forms

Water is the most commonly used solvent due to its physiological compatibility and lack of toxicity.
It possesses a high dielectric constant to ensure dissolution of ionisable materials.
However, water may not be suitable for extracting active constituents from vegetable sources.
Types of pharmaceutical water:
- Purified water: boiled and cooled immediately before use to eliminate microorganisms.
- Water for injections: pyrogen-free distilled water, sterile.
Other solvents include:
- Ethanol
- Isopropyl alcohol
- Glycerol
- Propylene glycol
- Sorbitol
- Syrup

Cosolvency: Using combinations of solvents, often improving drug solubility more than predicted from individual solubility.
pH control: altering pH to enhance solubility. Weak acids increase solubility at higher pH, while weak bases increase at lower pH.
Solubilization: Employing surface-active agents (SAAs) to increase solubility (e.g., micelles for non-polar compounds).

Converting poorly soluble drugs into salt forms to improve solubility (e.g., sodium salts of hydrocortisone, prednisolone, and betamethasone).
Producing water-soluble derivatives.

Buffers: Used to maintain consistent pH, important for stability and compatibility with other ingredients.
Isotonicity modifiers: Used to adjust the osmotic pressure of solutions, preventing pain and irritation on mucous membrane application (e.g., dextrose, sodium chloride).
Viscosity enhancement: Increasing the viscosity of aqueous-based topical solutions to enhance stay time on skin or in the eyes (e.g., gums such as starch, alginates, xanthan gum, cellulose derivatives.
Preservatives: Prevents microbial growth (e.g., parahydroxybenzoates).
Reducing agents and antioxidants: Used to control oxidation (e.g., sodium metabisulphite)
Sweetening agents: Sucrose is commonly used (e.g. sorbitol mannitol glycerol also have sweetening power).
Flavours and perfumes: Used for palatability
Colours: for easy product recognition.
Miscellaneous solvents: Isopropyl myristate, Isopropyl Palmitate, Xylene.

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