pharmaceutical sciences

• The adsorption at the various interfaces between solids, liquids and gases results in changes in the nature of the interface which are of considerable importance in pharmacy.
• The lowering of the interfacial tension between oil and water phases facilitates emulsion formation.
• The adsorption of surfactants on insoluble particles enables these particles to be dispersed in the form of a suspension.
• The adsorption of surfactants on solid surfaces enables these surfaces to be more readily wetted.
• Micellar solutions are stable dispersions within the true colloidal size range.
• Suspensions may be stabilized if the flocculation of the dispersed particles is controlled by the addition of electrolytes or ionic surfactants.
• Colloids can be broadly classified as lyophobic (solvent hating) (hydrophobic in aqueous systems), lyophilic (hydrophilic in aqueous systems), association colloids, and suspensions.
• Aqueous surfactant solutions form micelles when the concentration of surfactant exceeds a critical value, termed the critical micelle concentration, determined by the chemical structure of the surfactant and the external conditions.
• The incorporation of insoluble compounds within micelles of the surfactant can lead to the production of clear solutions.
• Dispersed systems consist of particulate matter, known as the dispersed phase, distributed throughout a continuous medium.
• The dispersed material may range in size from particles of atomic and molecular dimensions to particles whose size is measured in millimetres.
• Dispersions are generally classified as Molecular dispersions, Colloidal dispersions, and Coarse dispersions.
• The size of the particles has a great effect on the properties of a mixture.
• Mixtures get classified as solutions, suspensions, or colloids based on particle size.
• To improve the dispersibility of insoluble drug particles, agents can be used to flocculate the agents.
• Stoke's equation applies only to spherical particles in a very dilute suspension (0.5 to 2 gm per 100 ml), particles which freely settle without collision, and particles with no physical or chemical attraction.
• In a deflocculated system, the individual particles exist as separate entities.
• g is the acceleration due to gravity.
• Deflocculated suspensions contain particles exist as separate entities, have a low rate of sedimentation, sediment forms slowly, supernatant liquid is not clear, and sediments become very close packed as the particles repulse between each other.
• ρo is the density of the disperse media.
• ρs is the density of the disperse phase.
• η is the viscosity of the disperse medium.
• In a flocculated system, the individual particles are contacting with each other to form loose aggregates and create a network-like structure.
• Flocculated suspensions contain particles exist as loose aggregates, have a high rate of sedimentation, sediment forms rapidly, are supernatant liquid is clear, and consist of loosely packed particles possessing a network structure.
• Diameter of particle (d) is a key parameter in Stoke's equation.
• When substances dissolve and form a homogeneous mixture, the mixture is called a solution.
• The substance that there is more of in a solution is called the solvent.
• Drugs which degrade in aqueous solution may be suspended in a nonaqueous phase.
• Reasons for preparing suspensions include the drug being insoluble in the delivery vehicle, to mask the bitter taste of the drug, to increase drug stability, to achieve controlled/sustained drug release, to increase rate of dissolution in GIT as compared to solid dosage forms, and to prolong the action of a drug by preventing rapid degradation in the presence of water.
• Too large or too small particles should be avoided as they will settle faster at the bottom of the container and impart a gritty texture to the product and cause irritation if injected or instilled to the eye.
• The rate of sedimentation is expressed by Stoke’s equation: 𝑉 = 𝑑 2 ρs − ρo η V.
• Particles > 5 μm impart a gritty texture to the product and also cause irritation if injected or instilled to the eye.
• This occurs because the particles are too large to remain permanently suspended in the vehicle.
• Particle size of any suspension is critical and must be reduced within the range.
• Too fine particles will easily form hard cake at the bottom of the container.
• When the drug is unstable in contact with the vehicle, suspensions are prepared immediately prior to use.
• In an ideal situation, particles should settle easily and can be resuspended by a moderate amount of agitation.
• Particles > 25 μm may block the needle.
• Sedimentation is the settling of particles or floccules under gravitational force in a liquid dosage form.
• The other substance in a solution is called the solute.