Solutions in Therapy Flashcards
Solutions
are liquid preparations containing one
or more chemical substances dissolved in a suitable solvent or mixture of mutually miscible solvents
Solutions are often classified
due their composition or use
Solution examples
Syrups (aqueous with sugar), hydroalcoholic (water + ethanol), elixirs, tinctures,
etc.
– Oral, otic, ophthalmic, topical, etc
• Since a medicinal agent is administered in solution, it is usually assumed:
That the agent, as well as other solutes, are soluble or at least partially aqueous
soluble
Since it is already in solution, it is expected that
absorption occurs faster than from a solid or suspension dosage form of the same medicinal agent
– Pharmacist is aware of the
solubility and stability of each solute in the solution
to avoid chemical and physical interactions that will affect the product
• Solubility
The amount of solute that can dissolve in a given quantity of solvent at
a particular temperature
A saturated solution is
one that contains the maximum quantity of dissolved solute
at a given temperature
Solute-solute and solvent-solvent forces must
be overcome by solute-solvent attractive forces for dissolution to happen
Solubility may be increased by selecting a
different solubilizing agent, different
chemical salt form, alteration of the pH of the solution or substitution in part or in
whole of the solvent
An increase in temperature usually results
in an increase in solubility
Prediction of solubility is based upon
molecular structure and functional groups
– Like dissolves like
Salts of monovalent cations (Na, K, Li, NH4) are generally
water soluble
Salts of divalent cations (Ca, Mg, Hg) are
often less soluble
Halogen groups and increases in molecular weight tend to
decrease water solubility
Organic compounds may be somewhat more aqueous soluble if they
contain
polar groups that are capable of hydrogen bonding
Greater the number of polar groups
, the better likely the aqueous solubility
Polar groups include: -OH, -CHO, -COOH, -C=O, -NO2, -NO3
, -NH2
, -SO3H
Choice of solvents is based upon factors such as
solubility, clarity, toxicity,
compatibility with other formulation components, odor, color, cost and
route of administration
Co-solvents are often employed
– To enhance solvation ability of water
– To contribute to a product’s chemical and/or physical stability
Examples of co-solvents
o Ethyl alcohol, glycerin and propylene glycol often used
Alcohol
Also called ethyl alcohol, ethanol
-94.9-96% C2H5OH v/v
-
Alcohol is
Miscible with water and is able to dissolve many water insoluble ingredients
such as drug substances, flavorants, colorants and antimicrobial preservatives
Ethanol may act as a
antimicrobial alone or with other preservatives
FDA limits alcohol content in OTC oral products
Concern about undesirable pharmacologic and toxic effects
– Limits:
❖For children < 6 years of age – 0.5%
❖For children 6-12 years of age – 5%
❖For children > 12 years of age and adults – 10%
Glycerin, USP
Also called glycerol
- is a natural compound derived from vegetable oils or animal fat
- Miscible with water and alcohol
Glycerin characteristics
- Clear syrupy liquid with a sweet taste
- Has preservative properties at higher concentrations
- Used as a stabilizer and an auxiliary solvent in conjunction with water or alcohol
• Used in many internal preparations
Propylene Glycol, USP
Clear, viscous liquid
• A synthetic product obtained from the hydration of propylene oxide
• Miscible with water and alcohol
• Frequently substituted for glycerin in modern pharmaceutical formulations
Purified Water, USP
s obtained from EPA compliant water treated mainly by distillation, ion exchange or reverse osmosis
- Not intended for use for parenteral administrations (i.e., injections)
Note abt Purified water
Ordinary drinking water from the tap is not acceptable for the manufacture
of most aqueous preparations because of possible incompatibilities
between dissolved solids and the medicinal agents
Water permitted for parenteral administration:
Water for Injection, USP;
Bacterostatic Water for Injection, USP; Sterile Water for Injection, USP
Strengths of preparations are usually expressed
in terms of percent strength
To hasten the dissolution of a slow dissolving material, one may try to:
- Apply heat
- Reduce particle size of solute
- Use a solubilizing agent
- Vigorously agitate mixture (effective stirring)
- Lower viscosities of solvents if not only aqueous
Note:
Increased temperatures cannot be maintained for pharmaceuticals. Also, elevated temperatures may result in loss of volatile co-solvents (e.g., alcohol) and increase in the rate of degradation of drug or excipients.
Ratio strength weight in volme
-:- w/v Grams of constituent in stated milliliters of preparation