Solvents for Liquid Preparations
The following agents find use as solvents in the preparation of solutions.
  1. Purified Water, H2O
    Purified water has the widest range of usefulness of all the solvents employed in pharmaceutical dispensing or manufacturing, because of lack of toxicity, physiological compatibility, and its ability to dissolve a wide range of materials. It is a good solvent for most inorganic and organic

    Purified Water, USP, is obtained by distillation, ion exchange treatment, reverse osmosis, or other suitable process. When evaporated to dryness, it must not yield more than 0.001% of residue (1 mg of solids per 100 mL of water). Thus, purified water has only 1% as much dissolved solids as tap water. Purified Water, USP, is intended for use in the preparation of aqueous dosage forms except those intended for parenteral administration (injections). Water for Injection, USP; Bacteriostatic Water for Injection, USP; or Sterile Water for Injection, USP, is used for injections.
  2. Alcohol USP, Ethyl Alcohol, Ethanol (C2H5OH)
    Primary and good solvent for many organic substances both natural and synthetic. Together with water it forms a hydroalcoholic mixture that dissolves both alcohol-soluble and water-soluble substances, a feature especially useful in the extraction of active constituents from crude drugs. A most widely used solvent particularly for external application.

    Alcohol has been well recognized as a solvent and excipient in the formulation of oral pharmaceutical products. Certain drugs are insoluble in water and must be dissolved in an alternative vehicle. Alcohol is often preferred because of its miscibility with water and its ability to dissolve many water-insoluble ingredients, including drug substances, flavorants, and antimicrobial preservatives. Alcohol is frequently used with other solvents, such as glycols and glycerin, to reduce the amount of alcohol required. It is also used in liquid products as an antimicrobial preservative alone or with parabens, benzoates, sorbates, and other agents.

    It is particular useful for the extraction of crude drugs being more selective than water. Alcohol, USP, is 94.9 to 96.0% by volume (i.e., v/v) when determined at 15.56°C. Concern has been expressed over the undesired pharmacologic and potential toxic effects of alcohol when ingested in pharmaceutical products, particularly by children. For OTC oral products intended for children under 6 years of age, the recommended alcohol content limit is 0.5%; for products intended for children 6 to 12 years of age, the recommended limit is 5%; and for products recommended for children over 12 years of age and for adults, the recommended limit is 10%.
  3. Dehydrated Alcohol
    99.5% absolute alcohol is partially free from water. 
  4. Diluted Alcohol NF
    Diluted Alcohol NF prepared by mixing equal volume of Alcohol USP and purified water. Diluted alcohol is a useful hydroalcoholic solvent in various pharmaceutical processes and preparations.
    The final volume of such mixtures is not the sum of the individual volumes of the two components because the liquids contract upon mixing; the final volume is generally about 3% less than what would otherwise be expected. Thus, when 50 mL of each component is combined, the resulting product measures approximately 97 mL. It is for this reason that the strength of Diluted Alcohol, NF, is not exactly half that of the more concentrated alcohol but slightly greater, approximately 49%.
  5. Alcohol, Rubbing
    Rubbing alcohol contains about 70% of ethyl alcohol by volume the remainder consists of water, denaturants with or without color additives and perfume oils and stabilizers.

    Each 100 mL must contain not less than 355 mg of sucrose octaacetate or 1.4 mg of denatonium benzoate, bitter substances that discourage accidental or abusive oral ingestion.

    The product is volatile and flammable and should be stored in a tight container remote from fire. It is employed as a rubefacient externally and as a soothing rub for bedridden patients, a germicide for instruments, and a skin cleanser prior to injection. It is also used as a vehicle for topical preparations. Synonym: alcohol rubbing compound.
  6. Glycerin USP ( Glycerol) CH2OH•CHOH•CH2OH
    Glycerin  is a clear syrupy liquid with sweet taste. It is miscible both with water and alcohol. Excellent solvent for tannins, phenol and boric acid. It is used in many internal preparations. 10% water-containing glycerin no irritation. It (>30%)has a preservative qualities and is often used as a stabilizer and as an auxiliary solvent in conjunction with water or alcohol. As a solvent, it is comparable with alcohol, but because of its viscosity, solutes are slowly soluble in it unless it is rendered less viscous by heating.
  7. Propylene Glycol CH3CH(OH)CH2OH
    Propylene Glycol  is a viscous liquid, miscible in water, acetone, alcohol and chloroform . It is frequently substituted for glycerin in modern pharmaceutical formulations. Mixture of propylene glycol and water can derease the hydrolysis of drug substance and increase stability.
  8. Polyethylene glycol 400
    Polyethylene glycol 400 is miscible in water, acetone alcohol and other glycols
  9. Chloroform
    Chloroform is miscible with alcohol, ether, benzene, hexane and both fixed and volatile oils
  10. Acetone
    Acetone is miscible with water, alcohol, ether, chloroform and most of the volatile oils.
  11. Dimethyl sulfoxide (DMSO)
    This is a highly polar compound and is thought to aid the penetration of drugs through the skin. A broad range of substance can be dissolved in it, called Alcahest.
  12. Fatty Oils
    Including sesame oil, castor oil, cottonseed oil, soya oil, maize oil, olive oil. Commonly for external use: nasal drops, lotion and etc
    For internal: VA and VD solutions
  13. Isopropyl myristate
    Isopropyl myristate is oily materials used as solvents for external use particularly in cosmetics where their low viscosity and lack of greasiness make them pleasant to use.
  14. Isopropyl Rubbing Alcohol
    Isopropyl rubbing alcohol is about 70% by volume isopropyl alcohol, the remainder consisting of water with or without color additives, stabilizers, and perfume oils. It is used externally as a rubefacient and soothing rub and as a vehicle for topical products. This preparation and a commercially available 91% isopropyl alcohol solution are commonly employed by diabetic patients in preparing needles and syringes for hypodermic injections of insulin and for disinfecting the skin.