Liquid Dosage Forms: Part 2 (Suspensions, Emulsions and Solutions)

What is the composition of Emulsions and Creams?

- Polar phase (e.g., water)

- Non-polar phase (e.g., oil)

- Emulsifier

What are the characteristics of Emulsions and Creams?

- A thermodynamically unstable system consisting of at least two immiscible liquid phases

- One liquid phase is dispersed as globules (the dispersed phase) in the other liquid phase (the continuous phase)

- Both phases are stabilized by the presence of an emulsifying agent

In Emulsions and Creams, what are some signs of instability?

- Breaking

- Coalescence

- Creaming

- Flocculation

Surface-Active Agents (i.e., Surfactants)

Molecules or ions that are adsorbed at interfaces. In this case, the interface between water and oil

The tendency of an amphiphile to be predominantly hydrophilic, lipophilic, or reasonably well-balanced between these two extremes depends on WHAT?

Depends on the number and nature of the polar and non-polar groups present

What are the 2 most common surfactants that act as emulsifiers?

- Tween

- Span

HLB (Hydrophilic-Lipophilic Balance)

- An arbitrary scale of values devised by Griffin to measure the HLB of surfactants.

- The higher the HLB value, the more hydrophilic it is

Required hydrophile-lipophile balance, RHLB

*The oil phase of an oil-in-water emulsion requires a specific HLB

(A different RHLB is required to form a water-in-oil emulsion from the same oil phase)

Formula for %Surfactant with higher HLB

RHLB - HLB(low)/HLB(high) - HLB(low) x 100

Pharmaceutical Excipients for Emulsion: Maintaining the appearance

- Color

- Consistency

- Preservatives

Pharmaceutical Excipients for Emulsion: Protecting the active species

- Buffers

- Antioxidants

Pharmaceutical Excipients for Emulsion: Disguising the unpleasant taste/smell

- Sugar

- Flavoring agents

- Percent oil vs. water

Solution

Liquid preparations that contain one or more chemical substances dissolved, i.e., molecularly dispersed, in a suitable solvent or mixture of mutually miscible solvents

What is a true Solution?

- a mixture of two or more components that form a homogeneous molecular dispersion

- One-phase system

Is milk a solution?

NO

What are the characteristics of a solution?

- route of administration: oral; topical; parenteral

- solvent: spirits, tinctures, waters

- dosage: teaspoon; tablespoon

Solutions by Solvent system: Waters, Aromatic

saturated aqueous

Solutions by Solvent system: Spirits

Solutions of volatile substances (alcoholic or hydro alcoholic)

Solutions by Solvent system: Elixirs

Sweet hydro alcoholic; Phenobarbital Elixir, Digoxin Elixir

Solutions by Solvent system: Syrup

Aqueous. Usually sweetened with sucrose or sorbitol

Solutions by Solvent system: Tinctures

An alcoholic extract or solution of a nonvolatile substance

What is the effect of temperature on Solutions?

Solubility can increase or decrease

(endothermic vs. exothermic)

Solvents: Ethyl alcohol

- Next to water is the most useful solvent in pharmacy.

- It is used as a primary solvent for many organic compounds

- 94.9 to 96.0% by volume when determined at 15.56° C, the U.S. government's standard temperature for alcohol determinations

Solvents: Dehydrated Alcohol

- Contains NOT less than 99.5%

- Is used when an essentially water-free alcohol is desired

Diluted Alcohol, NF

Prepared by mixing equal volumes of Alcohol USP and Purified Water USP

What is the final volume of a mixture between Alcohol USP and Purified Water USP?

The final volume is generally about 3% less than what would otherwise be expected.

What are the contents of rubbing alcohol?

- 70% ethyl alcohol

- Remainder consists of water, denaturants with or without color additives, perfume oils, and stabilizers

For Rubbing Alcohol, each 100mL must conatin NOT less than how many mgs of sucrose octa-acetate or 1.4 mg of denatoniumbenzoate, bitter substances that discourage accidentalor abusive oral ingestion?

355mg

How does the use of this denaturant mixture (rubbing alcohol) affect the separation of ethyl alcohol from the denaturants?

It makes the separation of ethyl alcohol from the denaturants virtually impossible with an ordinary distillation apparatus

Because the separation of ethyl alcohol from the denaturants is virtually impossible, how does this affect beverages with alcoholic content?

This discourages the illegal removal for use as a beverage of the alcoholic content of rubbing alcohol.

Propylene glycol

* a solvent and has preservative properties

- In some instances, it combines the advantages of both glycerin and ethyl alcohol

- It has greater power to inhibit mold growth and fermentation.

- Came into use as a suggested replacement when glycerin was in short supply during World War II.

What is Propylene glycol's functional category?

- An antimicrobial preservative, humectant, plasticizer, solvent, stabilizer for vitamins, and a water-miscible cosolvent.

Why is propylene glycol a better solvent than glycerin?

Will dissolve a variety of drugs, including corticosteroids, phenols, sulfonamides, barbiturates, vitamins (A and D), most alkaloids, and many local anesthetics

For intravenous administration, formulations containing 35% propylene glycol can cause what in humans?

Hemolysis (breakdown of red blood cells (erythrocytes) in the bloodstream)

Syrup

mask bad taste, highly viscose (thick)

Sirupus simplex

64 sucrose, 36 water, heat water, filter

Diabetic persons

Exchange with tagatose or non-sugars: Sorbitol 64%, glycerin, propylene glycol