Pharmaceutical Solutions and Dosage Forms

Oral Solution: Taken through the mouth
Otic Solution: Instilled in the ears
Ophthalmic Solution: Instilled into the eye
Nasal Solution: Instilled into the nose
Topical Solution: Applied over skin surface
Rectal and Vaginal Solutions: Enema and douche for rectal/vaginal administration

Syrups: Aqueous solutions with sugar
Elixirs: Sweetened, hydroalcoholic (water & ethanol) solutions
Spirits: Alcoholic or hydroalcoholic solutions of volatile substances
Tinctures: Alcoholic or hydroalcoholic solutions prepared from vegetable materials or specific chemicals

Easy to swallow for children and elderly
Faster action compared to tablets, capsules, suspensions (Solutions > Suspensions > Capsules > Tablets)
Uniform dose due to homogenous distribution of medication
Dilute irritating effects of some drugs (e.g., KCl, aspirin)

Unpleasant taste or odor difficult to mask
Bulky to carry around
Requires accurate measuring device for correct dosage -Poor stability for drugs in aqueous solution
Suitable medium for microbial growth

Water: Most common solvent in pharmaceuticals due to:
- Lack of toxicity
- Physiological compatibility
- Ability to dissolve a wide range of materials

Tap Water: Suitable for drinking, contains dissolved & undissolved matter, including microorganisms
Purified Water: Fewer solid impurities than tap water, suitable for pharmaceutical use

Chemical stability of a drug: Depends on pH, optimal solubility may not match optimal stability
pH of Solutions: Parenteral and ophthalmic solutions need controlled pH to prevent pain and irritation
Preservative activity: Affected by pH altering its ionization
Concentration of co-solvents: Inclusion of alcohol or propylene glycol lowers dielectric constant of vehicle, increasing solubility of unionized drug

Solubilization:
- Using surface active agents (SAAs) with an HLB value >15
- SAAs must be non-toxic, non-volatile, non-irritant, miscible with solvent, compatible with other ingredients, and free from disagreeable odor and taste
- Example: Polysorbates (Tweens) for fat-soluble vitamins
Complexation:
- Interaction of poorly soluble drug with a soluble material to form a soluble complex
- “Hydrotropy”: Increase in aqueous solubility by adding additives
- Example: Iodine with 10-15% polyvinyl pyrrolidone (PVP) solution [BETADINE]
Chemical Modification:
- Production of a water-soluble derivative of the drug
- Example: Chloramphenicol sodium succinate for parenteral administration (converted to active base)
Particle Size Control:
- Decreasing particle size increases surface area leading to increased solubility

Used when drugs are poorly soluble or unstable in aqueous systems
Depot Therapy: Intramuscular injection of solutions in oils creates a slow-release reservoir

Toxicity, irritancy, sensitization potential: Important for safety
Flammability: Important for handling and storage
Cost: A factor in manufacturing
Stability: Ensuring the solvent doesn't degrade the drug
Compatibility with other excipients: Ensuring the chosen solvent doesn't interfere with other components in the formulation

Alcohol, USP (Ethyl Alcohol, Ethanol):
- Widely used solvent in pharmacy
- Dissolves many organic compounds
- Together with water, forms hydroalcoholic mixtures for dissolving both alcohol-soluble and water-soluble substances
- Used for extraction of active constituents from crude drugs
- Alcohol, USP: 94.9-96.0% C2H5OH v/v
- Dehydrated Alcohol, USP: 99.5% C2H5OH v/v

Miscible with water
Dissolves many water-insoluble ingredients (drugs, flavorants, antimicrobial preservatives)
Used as a preservative alone or with parabens or benzoates

Undesired pharmacologic effects
Potential toxic effects, particularly in oral use
Content limit: FDA sets a maximum of 0.5% alcohol for OTC oral products intended for children under 12 years
Diluted Alcohol: Equal volumes of alcohol and Purified Water, resulting in a final volume approximately 3% less than expected due to contraction upon mixing
Alcohol, Rubbing: Approximately 70% ethyl alcohol by volume, with water, denaturants, color additives, perfume oils, and stabilizers
Isopropyl Rubbing Alcohol: Approximately 70% isopropyl alcohol by volume, with water, color additives, stabilizers, and perfume oils, used for external use as rubefacient and vehicle
Glycerin, USP (Glycerol): Clear, viscous liquid with a sweet taste, miscible with water & alcohol, comparable to alcohol as a solvent but slower due to viscosity, possesses preservative qualities
Propylene Glycol: Viscous liquid, miscible with water and alcohol, widely used drug solubilizer in topical, oral, and injectable medications.