Lab 2 Flashcards
Must all drugs be soluble in water? explain
ALL drugs must be soluble in water to some extent, regardless of dosage form.
This is so because it enables systemic absorption and therapeutic response.
The dosage form used for administering a drug is generally selected based on….
the drug’s solubility
What is done if a drug is extremely insoluble?
more soluble derivatives of the parent drug are prepared by salt formation and chemical complexation
A “true solution” is formed when….
the solute molecules completely dissolve in the solvent to give a clear, transparent, homogeneous liquid
In a true solution, can the solute and solvent be separated by filtration? Is the solution able to transmit light?
A true solution CANNOT be separated by filtration. A true solution IS able to transmit light
What is a colloidal solution?
a colloidal solution is a visibly clear, transparent homogenous liquid. However, a colloidal solution reflects light (Tyndall effect)
What is a saturated solution?
a saturated solution is a solution which contains the MAXIMUM amount of dissolved solute (ie: at its maximum solubility)
What is a supersaturated solution?
a supersaturated solution forms when the quantity of solute is greater than its solubility
Both saturated and supersaturated solutions tend to be…..
UNSTABLE and very likely to crystallize or precipitate with changes in temperature, addition of other ingredients, and loss of solvent (evaporation)
Addition of other substances in saturated and supersaturated solutions can result in precipitation and crystallization. What is the term for these added substances?
excipients
Differentiate between precipitation and crystallization
Precipitation is the formation of very small particles of the solute
Crystallization occurs when these particles have a well-defined, crystalline structure
Most substances are (endothermic or exothermic) when dissolving
endothermic (absorb heat)
If a substance is endothermic when dissolving, will the temperature of the solution increase or decrease?
decrease since the substance is absorbing heat from the solution
In the case of an endothermic solute, will its solubility increase or decrease with increasing heat?
solubility will increase
Pressure affects the solubility of _____ but generally does not affect the solubility of ___
Pressure affects the solubility of GASES but generally does not affect the solubility of SOLIDS AND LIQUIDS
Solubility _______ with increasing molecular size
decreases
Water is the solvent. Will a molecule with hydrophobic groups be soluble?
no
Water is the solvent. If the solute has polar groups (acids, esters), will it be soluble?
yes
Solutes exist as ____ and ___ forms
amorphous and crystalline
Solutes exist as amorphous and crystalline forms. Which is more soluble and why?
the amorphous form is more soluble. this is so because crystalline polymorphs have well-fitted molecular arrangements that are less likely to interact with the solvent
Polymorphic changes can occur during….
precipitation
Dielectric constant is a measure of…
the solvent’s ability to separate opposing molecular charges
The higher the dielectric constant, the _____ the polarity of the solvent and the _____ likely it is to interact with nonpolar solutes
the higher the dielectric constant, the GREATER the polarity of the solvent and the LESS likely it is to interact with nonpolar solutes
Explain the pros and cons of using organic compounds as solvents
pro – they have low dielectric constants and are thus able to dissolve non polar solutes
con — they are toxic in high concentrations
What is the purpose of the cosolvent system?
The cosolvent system consists of several solvents to create an aqueous mixture with a desirable dielectric constant, but without the toxic effects of organic compounds. This system decreases the difference between the polarity of the solute and solvent
The apparent dielectric constant of a mixture of solvents (cosolvent system) can be calculated which 2 ways?
the algebraic and allegation methods
What is another word for “particle size reduction”
pulverization
What is the purpose of pulverization
pulverization increases the surface area of the drug that comes in contact with the solvent and thus increases the dissolution rate
Does reducing particle size increase the intrinsic solubility of a substance?
NO
Explain the pros and cons of agitation
pro — stirring (agitation) increases the rate of dissolution
con — excessive agitation can increase entrapment of air and foaming which could result in degradation of a drug that is easily oxidized, as well as errors in volume/concentration of the product
Hydrophobic powders do not mix well with water due to _____. What can be done to help the solubilization process in this case?
surface tension. Wetting agents can increase the contact of hydrophobic drugs with water and aid in the solubilization process
Pharmaceutical solutions are….
solids dissolved in a liquid vehicle (usually water of a combination of solvents and ingredients to dissolve the solids)
Gives some pros and cons of pharmaceutical solutions vs solid dosage forms
pro— solutions provide a faster onset of activity, is homogenous, and provides uniform flexible dosing. Also has several routes of administration (oral,IV) and is useful for patients who have difficulty swallowing pills
con— more likely to have stability and appeal (taste) issues. more likely to leak
What is intrinsic solubility?
the solubility of the drug in a solvent when the drug is in an uncharged state
Name the 5 USP descriptive terms for solubility
parts of solvent (mL) needed to dissolve 1 part (g) of solute
Very soluble = less than 1mL
Freely soluble = 1-10mL
Soluble = 10-30mL
Sparingly Soluble = 30-100mL
Slightly soluble = 100-1000mL
What are 3 techniques used to improve the solubility of drugs in aqueous solutions?
- cosolvent
- adjusting pH
3.using solubilizers and complexing agents
cosolvents are usually…….
alcohols or other organic solvents . Added to the primary solvent in small amounts to increase the solubility of a poorly soluble compound
Selecting of the co-solvent is based on…
the dielectric constant of the drug.
For good solubility, the difference of the dielectric constant between the drug and the solvent mixture should be small
