Solutions

What is a solution?

A solution is a homogeneous mixture in which one substance (solute) is completely dissolved in another substance (solvent).

Four characteristics of a solution

1. Thermodynamically stable

2. One-phase system - You cannot visually distinguish the dissolved solute from the solvent.

3. Composed of two or more components

4. Solute is completely dissolved

What can act as a solute? (6)

• active drug components,

• flavoring,

• coloring agents,

• preservatives,

• and stabilizers or buffering salts.

what is most common solvent

Water most common solvent for solutions, but
ethanol, glycerin, propylene glycol, isopropyl
alcohol or other liquids may be used,
depending on the product requirements

Advantages as a dose form for solutions

 Solutions are completely homogenous
 Immediately available for absorption into the body
 Flexible in terms of dose adjustment
 May be used by any route of administration
 Can be administered to patients who cannot swallow
tablets or capsules

Disadvantages as a dose form.(5)

 Drugs less stable when in solution, compared to solid a state
 Some drugs not soluble in solvents that are acceptable for
pharmaceutical use
 Drugs with objectionable taste require taste masking
 Heavier and bulkier than solids so are difficult to handle,
package, transport, and store
 Require measurement by the patient or caregiver. Often
less accurate than individual solid dosage forms, such as
tablets and capsules

what is Noyes-Whitney equation

This equation describes the dissolution rate of a drug.

what does Pharmaceutical elegance mean

Pharmaceutical elegance means that a medication has an acceptable appearance, consistency, and overall quality.

• that the final product should be clear and free of unwanted particles.

how can you remove small particles in a solution?

Sometimes unwanted particles enter the solution from:

• Packaging materials

• Small amounts of degradation products

These unwanted particles can be removed through filtration, when appropriate.

why must you Never filter to remove undissolved solute

Imagine preparing a solution containing 100 mg of a drug.

Only 80 mg dissolves, while 20 mg remains as solid particles.

If you filter the solution, you would remove that undissolved 20 mg.

Result: The final solution would contain less drug than intended, potentially producing an incorrect concentration.

What is solubility?

Solubility is the maximum amount of a substance that can dissolve in a particular solvent at a specific temperature.

what interactions are made and disrupted during dissolution

1. Solute–solute interactions are disrupted

2. Solvent–solvent interactions are disrupted

3. Solvent–solute interactions form

what affects rate of dissolution but not solubility (2)

• Smaller particle size: Increases surface area, allowing the drug to dissolve faster.

• More stirring: Helps move dissolved drug away from the particle surface, increasing dissolution rate

what affects both dissolution and solubility and how

Temperature can affect both dissolution rate and solubility.

• Increasing temperature generally increases the dissolution rate of solids.

• Increasing temperature often increases the solubility of solid drugs, although there are exceptions.

how can pH affect solubility

Ionizable drugs are drugs that can gain or lose protons (H⁺), depending on the surrounding pH.

Because ionized drugs are generally more water-soluble than their unionized forms.

• Weak acidic drug + basic environment → More ionized → Greater aqueous solubility.

• Weak basic drug + acidic environment → More ionized → Greater aqueous solubility.

what are the steps of dissolution and which stage releases and aborobs energy

Step	Energy change	Reason
ΔH₁	Positive (+)	Energy needed to separate solvent molecules
ΔH₂	Positive (+)	Energy needed to separate solute particles
ΔH₃	Negative (−)	Energy released when solute–solvent interactions form

what is Entropy and what can it favour

• Entropy refers to the dispersal of energy and matter, often described simply as disorder.

Can favour dissolution, particularly when enthalpy changes are small.

What happens when both solute and solvent are polar?

Because both substances are polar, strong attractive interactions can form between them.

• Result: The polar solute can dissolve in the polar solvent.

What happens when a nonpolar solute mixes with a polar solvent?

have hard dissolving

• remember like dissolves like

  Solute	Solvent	Expected result
  Polar	Polar	Generally dissolves
  Nonpolar	Nonpolar	Generally dissolves
  Polar	Nonpolar	Generally poor solubility
  Nonpolar	Polar	Generally poor solubility

why does mixing 25 mL of one liquid with 25 mL of another liquid doesn't necessarily produce 50 mL of solution. (2)

1. Different intermolecular forces

2. Different molecular sizes and shapes

what is Displacement volume

Displacement volume is the volume contributed by a powder when it is mixed with a liquid during drug reconstitution.

Why is this important?

Imagine you incorrectly added 5 mL of diluent instead of 4.8 mL.

The final volume would be approximately 5.2 mL, meaning the drug concentration would be lower than intended.

what is Purified Water USP What are its properties??

Purified Water USP is water that has been treated to remove impurities so it meets pharmaceutical quality standards.

• Contains no added substances.

• Cannot contain more than 0.001% solids

how is purified water obtained (3)

• Distillation: Water is boiled, and the vapour is collected and condensed back into liquid, leaving many impurities behind.

• Ion exchange: Removes dissolved ions from water using special resins.

• Reverse osmosis: Forces water through a semipermeable membrane to remove impurities.

What is Alcohol USP?

In pharmacy, the term alcohol generally refers to ethanol (ethyl alcohol).

• Very useful solvent with preservative
  properties

Why is ethanol useful in pharmacy?

Some drugs do not dissolve well in water.

Ethanol can be used as a cosolvent, meaning it is combined with another solvent, such as water, to improve the drug's solubility.

Alcohol limits for children

Age	Maximum alcohol content in your slide
Under 6 years	0.5%
6–12 years	5%
Older than 12 years	10%

are methanol and isopropanol used in pharmacy compounding?

Methanol

• Highly toxic.

• it should never be used as a pharmaceutical solvent.

Isopropanol (isopropyl alcohol)

• Can be used in certain topical preparations.

• Not suitable for oral administration.

what is Propylene glycol (PG)

is a pharmaceutical solvent that helps dissolve drugs, especially those with poor water solubility.

• Miscible means two liquids can mix completely in all proportions to form a homogeneous solution.

What ingredients do oral solutions contain

• Sweeteners: Improve the taste of the medication.

• Preservatives: Help prevent microbial growth.

What are elixirs?

An elixir is a clear, sweetened, flavored hydroalcoholic oral solution containing medication.

Hydroalcoholic simply means the solution contains both:

• Hydro = Water

• Alcoholic = Alcohol (ethanol)

• elixirs can contain varying amounts of alcohol, up to approximately 30%. The alcohol helps dissolve certain medications that do not dissolve well in water alone.

• Propylene glycol may be used to
  replace some of the alcoho

what are Tinctures

Tinctures are hydroalcoholic solutions that contain relatively high concentrations of alcohol (ethanol).

Remember: Hydroalcoholic means the solution contains both water and alcohol. tinctures contain 15–80% alcohol.

• Diluting a tincture with water usually causes some dissolved ingredients to precipitate.

• Route of administration: Can be used orally or topically.

what does percipitation mean

Precipitation means a dissolved substance comes out of solution and forms solid particles.

what are Aromatic waters

Aromatic waters are clear aqueous solutions saturated with volatile oils.

• Aqueous: Contains water as the solvent.

• Saturated: Contains the maximum amount of dissolved substance under the given conditions.

• Volatile oils: Aromatic oils that readily evaporate and produce characteristic smells.

What are aromatic waters used for?

• Flavoring: Improve the taste of pharmaceutical preparations.

• Odor: Give pharmaceutical preparations a pleasant smell.

what are collodions

Collodions are liquid preparations that form a thin, flexible protective film when applied to the skin. contains

• pyroxylin

• alcohol and diethyl ether

What are collodions used for?

deliver keratolytic medications.

A keratolytic is a substance that helps break down and remove excess keratin from the skin.

• The film helps keep the medication in contact with the area being treated.

what are Syrups, what do they contain?

Syrups are concentrated aqueous preparations containing sugar or a sugar substitute.

• Water: Acts as the solvent.

• Sugar or sugar substitute: Provides sweetness.

• Flavoring agents: Improve taste.

• Medication: May be added to produce a medicated syrup.

not all syrups contain medication.

Why are syrups used in pharmacy?

Syrups can act as a vehicle.

A vehicle is an ingredient or preparation used to carry the active pharmaceutical ingredient.

For example, a pharmacist may add a compatible medication to a syrup base to make an oral preparation more palatable.

Why do syrups need preservatives?

The main reason is to prevent microbial growth, such as bacteria, yeast, and fungi.

What is free water?

Free water is the water available for microorganisms to use for growth.

• More free water: Microorganisms can grow more easily.

• Less free water: Microbial growth is inhibited.

amount of preservative needed depends on the amount of free water in the syrup.

How much preservative should be added?

• The preservative concentration must be high enough to prevent microbial growth.

• The concentration must be low enough to avoid toxicity.

Why is 85% sucrose important?

Simple syrup containing 85% sucrose is considered self-preserving.

What does self-preserving mean?

It means the syrup can inhibit microbial growth without needing an additional preservative.

how can it be self preserving, What happens if we dilute the syrup?

• The syrup contains a very high concentration of sugar.

• Sugar binds water and reduces the amount of water available to microorganisms.

• Microorganisms have difficulty growing because of the low water availability.

• 85% sucrose: Self-preserving.

• Less than 85% sucrose: Requires a preservative.

Commonly used preservatives for syrups include? (4)

 Alcohol
 Benzoic acid or Sodium benzoate 0.1-0.2%
 Potassium sorbate 0.1%
 Parabens (mix of methyl and propyl esters) 0.1%

To preserve diluted syrup with alcohol, need the following
facts to estimate amount of free water

18% alcohol will preserve free water
1 g of sucrose occupies 0.632 mL
1 g sucrose preserves 0.545 mL water

Which flavors mask different drug tastes?

Drug taste	Recommended masking flavors
Salty	Butterscotch, apricot, peach, vanilla, wintergreen mint
Bitter	Cherry, mint, anise
Sweet	Chocolate, vanilla, fruit, berry
Sour	Citrus flavors, raspberry

what are 3 main methods to prep for a syrup

Heat if no volatile or heat-liable components
May also use stirring without heat (agitation)
Percolation -

Must be careful with heat not to caramelize sucrose

what is Percolation

• Place sucrose in a suitable percolator.

• Allow purified water to pass gradually through the sucrose.

• Collect the resulting syrup.

• Continue until the required amount of syrup is prepared.

what is morphine and how can it be affected by pH

Morphine is a weak base - increase the pH of a morphine sulfate solution by adding an alkali (base), morphine may precipitate out of the solution.

• Low pH → more ionized → more water-soluble.

• High pH → more unionized → less water-soluble → possible precipitation.

what are examples of weak acids and how can pH affect them

1. amoxicillin

2. aspirin

• Low pH → more unionized → generally less water-soluble - may percipitate out of solution

• High pH → more ionized → generally more water-soluble.