Solutions Flashcards
What is the pharmacy relevance of dissolution?
Absorption
Formulation
Medicine incompatibility
In what state do drugs need to be in to be absorbed?
Aqueous
When can dissolution occur?
Dissolution can only occur if the attractive force between drug molecule and solvent molecule is greater than between the drug molecules itself.
What effects solubility of a solute structure?
Small change in molecular structure
Polarity
OH group
Salt formation
solute substituents
How do solute substituents alter solubility?
Charged functional groups are more hydrophilic and therefore more soluble.
What do polar solvents dissolve?
Dissolve ionic solutes by reducing the force of attraction between oppositely charged ions in crystalline solids.
What can semi-polar solvents dissolve?
Polar and non-polar substances
Solvent molecular dipole moment or H bonding groups enable polar solutes to be dissolved.
Induce a degree of polarity in non polar solvent molecules.
What can non polar solvents dissolve?
Dissolve non polar compounds only
Unable to break covalent bonds
Low dielectric constant and lack of H bonding groups prevent these solvents from dissolving ionic or polar solutes
What other factors determine solubility?
Temperature (rise in temp= more soluble)
Polymorphism/solvates/hydrates (less stable polymorphs are more soluble)
Particle size
pH
What phase are oral solutions in?
Monophobic
What are pharmaceutical solutions?
Liquid preparations in which the therapeutic agent and the various excipients are dissolved in the chosen solvent system
What is the chemical stability in solutions?
Low
How is absorption from an oral solution different from other oral dosage forms?
Rapid and complete with greater bioavailability
What are the advantages of liquid oral dosage forms?
Easily administered for individuals who have difficulty in swallowing
Immediately available for absorption
Taste-making of bitter therapeutic agents
What are the disadvantages of liquid oral dosage forms?
Unsuitable for therapeutic agents that are chemically unstable in the presence of water
Poor solubility of certain therapeutic agents
Expensive to shopping as they are bulky
What are the excipients in solution?
Co-solvents
Antioxidants
Antimicrobial preservatives
pH adjusters
Isotonic adjusters
Viscosity enhancers
Chelating agents
Flavourings
Sweeteners
Colouring agents
What needs to happen to water for it to be used in non parenteral solutions?
Purified by distillation, ion exchange or reverse osmosis
What needs to happen to water to be able to use it for injections?
Further purified to remove pyrogens
What is the challenge when discussing drug solubility?
Attainment if homogeneity in the formulation due to limited aqueous solubility of the therapeutic agent
What does high solubility at selected pH of formulation mean?
Readily incorporated into the vehicle and formulated as an oral solution
What does moderate solubility at selected pH of formulation mean
Solubility enhanced using co-solvents or by related methods
What does low solubility at selected pH of formulation mean?
Formulated as an alternative dosage form
What does the dissolution of a therapeutic agent in water involve?
Removal of a molecule of the drug from the solid state
Formulation of a cavity within the solvent
Accommodation of the drug molecule into the formed cavity
Hay are the physicochemical properties affecting the solubility of therapeutic agents?
Molecular weight
Particle size
Solubility
Number of hydrogen bonds
Hydrophilic groups
Crystalline/ amorphous properties
pH dependant
The degree of ionisation
What is the acceptable pH range for formulation of oral drug solution?
5 to 8
What is a co-solvent?
Liquid components into a formulation to enhance the solubility of poorly soluble drugs
What are cyclodexton complexation ?
Enzymatically modified starches composed of glycopyranose units which form a ring of either six, seven or eight units.
What are the purposes of excipients?
To facilitate the administration of the dosage form
To protect the formulation from issues regarding physical and chemical stability and to enhance the solubility of the therapeutic agent.
What are buffers used for as excipients?
To control pH
To enhance the stability
What are sweetening agents used for as excipients?
To increase palatability
What are colourants used for as excipients?
To import the proffered colour
What are flavourings used for as excipients?
To mask the taste
What are viscosity enhancing agents used for as excipients?
To ensure accurate measurements
What are antioxidants used for as excipients?
To enhance the stability
What are chelating agents used for as excipients?
To form complexes with heavy-metal ions
What are preservatives used for as excipients?
To control the microbial bio burden
What are antioxidants?
Molecules that exhibit higher oxidative potential than the therapeutic agents
What are lactulose oral solutions used for?
Lactulose is indicated for use as a laxative in the treatment of chronic constipation in adult or geriatric patients
What is the structure of lactulose oral solution?
A synthetic disaccharide derivative of lactose consists of one molecule of galactose and one molecule of fructose
What excipients are present in lactulose oral solution?
Purified water (lactulose is water-soluble)
What are oral syrups?
Highly concentrated, aqueous solutions of sugar or a sugar substitute
What are the major components of oral syrups?
Purified water
Sugar
What is not present in oral syrups?
No sweetening agent
No viscosity modifying agents
No preservatives
What are oral elixirs?
A clear, hydro alcoholic solution for oral use
Why is alcohol required in oral elixers?
Ensure all components remain in solution
Why is the alcohol present in oral elixers problematic?
For patients who wish to avoid alcohol.
What are the typical components in oral elixers?
Purified water
Alcohol
Polyol cosolvents
Sweetening agents
Flavouring and colourants
What is a phenergon elixer?
Alcohol free, sugar free antihistamine formulated for the use by children
What is contained within phenergon elixers?
Promethazine
What are linctuses?
Viscous preparations that contain the therapeutic agent dissolved in a vehicle composed of a high percentage of sucrose and other sweetening agents
What are mouthwashes and gargles used for?
For the treatment of infection and inflammation of the oral cavity
What does alcohol enhance in mouthwashes and gargles?
The anti microbial properties of the therapeutic agents
what goverens the attractive forces between solute and solvent?
the molecular structure of the solid and the nature of the solvent
what type of permittivity do polar solvents have?
relative permittivity
(frmerly known as the dielectric constant)
