Pharmacy Dosage Forms: Solutions and Disperse Systems

Dosage Forms

• Solutions: homogenous system where one or more solid is completely dissolved in a liquid (solvent)
• Dissolution process: transfer of solute from solid state to molecular or ionic state in a certain solvent

Disperse Systems

• Emulsions/creams: oil dispersed in water gives emulsion (liquid), fat dispersed in water gives cream (semi-solid)
• Both are hydrophobic, do not mix with water, and are stabilized with surfactants
• Suspensions: solid particles suspended or dispersed in a vehicle
  • Solid in liquid → oral suspension, ophthalmic suspension drops
  • Solid in gas → topical sprays, Inhalers

Surfactants

• Compounds that lower the interfacial tension between two liquids to stabilize it
• Cohesive forces: attraction forces between like molecules
• Adhesive forces: attraction forces between unlike molecules
• High cohesive force > adhesive force = immiscible liquid

Ointments

• Soft or semi-solid preparation containing a medicament dissolved in greasy or fatty base
• Applied: topically on skin or ophthalmic

Patches

• Medicated adhesive patch that is placed on the skin to deliver a specific dose of medication through the skin and into the bloodstream

Powders

• Particles are aggregate of molecules that bind to each other by a certain bond (cohesive/intermolecular forces)
• Amorphous powders: molecules in particles are randomly arranged
• Crystalline powders: molecules are arranged in a fixed repeated arrangement
• Polymorphism: Different crystalline forms of the same material (different arrangement in the crystal lattice)

Granules

• Aggregates of powders due to the addition of a liquid or a granulating solution
• Small particle size = High surface area = Faster dissolution rate

Solubility and Dissolution Rate

• Solubility: maximum amount to be dissolved in a certain volume of a solvent at constant conditions
• Dissolution rate: the amount dissolved of a solute by time / the rate of mass transfer to solution (dm/dt)
• Sucrose solubility: 2g/ml water, NaCl solubility: 0.36g/ml
• Sucrose dissolves slowly, NaCl dissolves at faster rates

Physical Terms

• Spreadability: ability of the material to be distributed over a large surface area
• Adsorption: atoms/ions/molecules from a substance adhere to a surface of the adsorbent
• Absorption: process in which a fluid is dissolved by a liquid or a solid (absorbent)
• Drug absorption: movement of a drug from its site of application into the bloodstream across biological membrane

Drug Administration by Oral Route

• Distribution: reversible transfer of a drug from one location to another within the body
• Drug metabolism: describe the biotransformation of pharmaceutical substances in the body so they can be eliminated more easily
• Drug elimination: removal of drugs from the body
• Partition coefficient: the distribution of solute between immiscible liquids
• Ratio between the concentration of the solute in two immiscible liquids at equilibrium

Osmosis and Osmotic Pressure

• Osmosis: transfer of water from high water potential to low water potential
• Osmotic pressure: pressure exerted by solutes in a solution that pulls water by osmosis
• Semipermeable membrane: layer that only certain molecules can pass through
• Pharmaceutical Solutions should be isotonic with body fluids to prevent tissue damage

Rheology

• Viscosity: expression of the resistance of a fluid to flow; the higher the viscosity, the greater is the resistance
• pH value: measure of hydrogen ion concentration, measure of acidity or alkalinity of a solution
• pH value of dosage forms should be within a certain range so that it won’t be irritable to biological tissue

Learn about the characteristics of solutions, dissolution process, and disperse systems including emulsions and creams in pharmacy dosage forms.