1: Solvents for Solution Formulation Notes

Water is the most widely used solvent for pharmaceutical products due to its versatility and safety.
Advantages:
- Lack of toxicity, making it safe for internal and external use.
- Physiological compatibility, meaning it does not typically cause adverse reactions in the body.
- Polarity and ability to form hydrogen bonds, which allows it to dissolve a wide range of materials.
- Can dissolve a wide range of materials, including polar and ionic substances.
Types:
- Potable water: Regular tap water that may contain impurities and is unsuitable for pharmaceutical use.
- Purified water: Obtained through purification processes like distillation, ion exchange, or reverse osmosis; meets specific purity standards.
- Water for preparation: Must be free from microorganisms and pyrogens to ensure product safety and stability.
- Water for injection (parenteral): Highly purified water that is sterile and pyrogen-free, used for injectable products.

Ethanol (ethyl alcohol) is commonly used as a non-aqueous solvent, particularly for external preparations and as an antimicrobial agent.
Acts as a co-solvent for many preparations, enhancing the solubility of various substances.
Miscible with water as well as with organic solvents, making it an excellent co-solvent for both polar and non-polar compounds.
Hydroalcoholic solutions (diluted alcohol) can dissolve both water-soluble and many water-insoluble substances (drugs, flavorants, preservatives), improving formulation flexibility.
The percentage of alcohol can be reduced when glycols and glycerine are added, minimizing potential irritation and toxicity.
Preservative: 15% to 18% alcohol will prevent microbial growth in acidic and basic media, ensuring product stability.
Content limits in products intended for children:
- Under 6 years: 0.5%
- 6-12 years: 5%
- Over 12 years: 10%
Rubbing alcohol: ~70% EtOH or isopropyl alcohol in water (e.g., Isocol); used as a topical antiseptic and disinfectant.

Clear, odorless, viscous liquid.
Sweet taste, which can improve palatability in oral formulations.
Low toxicity, making it safe for various pharmaceutical applications.
Miscible with water and alcohol, enhancing its versatility as a solvent and co-solvent.
Used as a co-solvent with water or alcohol, humectant to retain moisture, moisturizer for topical products, preservative by reducing water activity, and stabilizer to prevent degradation.
Uses: Cough syrups, elixirs, expectorants, mouthwashes, skin care products, and suppositories.

Clear, odorless, viscous liquid.
Tasteless, making it suitable for oral and topical formulations.
Low toxicity, ensuring its safety in pharmaceutical products.
Miscible with water and alcohol, enhancing its utility as a solvent.
Less viscous than glycerin, which can improve the flow properties of formulations.
Used as a co-solvent, lubricant to improve manufacturing processes, humectant to retain moisture, moisturizer for topical applications, preservative by inhibiting microbial growth.
Uses: Same as for glycerin; also used in parenteral formulations.

Polyethylene glycol is a polyether compound derived from petroleum.
Clear, colorless, viscous liquid.
Tasteless, making it suitable for various pharmaceutical applications.
Hygroscopic, meaning it readily absorbs moisture from the air.
Miscible with water, enhancing its use in aqueous formulations.
Used as a solvent, co-solvent, and surfactant to improve the solubility and stability of drugs.

Syrups are concentrated aqueous solutions of sugar, typically sucrose.
Syrup BP is a solution of 66.7% sucrose in water, providing a high concentration for preservation.
May contain up to 85% of sugars, including sucrose, glucose, and fructose.
Capable of inhibiting bacterial growth due to high osmotic pressure.
Used as a co-solvent to improve drug solubility and as a sweetening agent to enhance palatability.