Compounding Suspensions in Pharmacy

Compounding Suspensions

• Suspensions are important pharmaceutical dosage forms, still widely used, often in emergency preparations
• They're used in various pharmaceutical products like ear drops, enemas, inhalations, lotions, and oral mixtures
• A suspension is a preparation where at least one active ingredient is suspended in a vehicle or pharmaceutical solvent
• According to the British Pharmacopoeia (BP), oral suspensions contain one or more active ingredients suspended in a suitable vehicle
• Suspending solids might settle but easily redisperse
• Suspensions may offer advantages like palatability for insoluble drugs, stability of insoluble drugs, easier swallowing of insoluble powders, faster absorption than solid forms, and the ability to prepare sustained-release formulations
• Disadvantages of suspensions in the context of comparing them to solutions include possible reduced accuracy of dose, potential negative impact from storage conditions, and being bulkier

Types of Suspensions

• Diffusible suspensions contain light powders that are insoluble or only slightly soluble in the vehicle. They disperse evenly upon shaking. Examples include Light Kaolin BP and Light Magnesium Carbonate BP
• Indiffusible suspensions contain heavy powders insoluble in the vehicle. They don't disperse evenly upon shaking for long, and the vehicle needs thickening to reduce the rate of settling. Examples include Aspirin BP, Calamine BP, and Zinc Oxide BP.

Formulation Considerations

• The most common vehicle for suspensions is water (H₂O)
• The density of the aqueous vehicle can be altered by adding sucrose or glycerol or a suspending agent.
• Other common additives include colorings, flavorings, and preservatives
• Common preservatives used include Benzoic Acid BP (0.1%) for internal use and Chlorocresol BP (0.1% w/v) for external use

Suspending Agents

• Natural polysaccharides: Acacia BP (gum from acacia trees), Tragacanth (dried gummy exudates from the Astragalus shrub), and Sodium alginate (from seaweed)
• Semi-synthetic polysaccharides: Methylcellulose BP (a methyl ether of cellulose)
• Clays: Bentonite
• Synthetic agents: Carbomer - primarily for external use
• Miscellaneous agents: Gelatin

Wetting Agents

• Added to facilitate suspensions of powders that have a tendency to float on the surface due to trapped air
• Forms a film at the liquid/air interface making the solid more receptive to the surrounding particle
• Wetting agents for internal use include polysorbates and sorbitan esters; for external use, quillaia tincture, or sodium lauryl sulfate

Emergency Formulations

• Compounders prepare liquid preparations if patients cannot swallow tablets/capsules
• Tablets/capsules will likely be crushed/opened to create the suspension form
• Tragacanth or compound tragacanth powders are suitable suspending agents for such applications.

Labeling

• "Shake the bottle" is a required label for all suspensions.
• Label "Not to be taken" on inhalations
• Label "For external use only" for external suspensions

General Preparation Method

A general method for preparing suspensions involves these steps:

1. Check the solubility of all solids in the mixture
2. Calculate the quantities of vehicle needed to dissolve soluble solids
3. Weigh all solids
4. Dissolve soluble solids in the vehicle in a beaker
5. Mix insoluble, diffusible powders in a mortar using a "doubling technique" and add the suspending agent
6. Add a small quantity of vehicle to the solid mixture in a mortar, mixing until a smooth paste forms
7. Add more vehicle to the paste; mix until a pourable consistency is reached
8. Transfer the mixture to a flask, noting the final volume
9. Rinse the mortar, adding rinsings to the flask
10. Add remaining liquid ingredients to the mixture
11. Make up to the final volume with the vehicle
12. Transfer the mixture gently into the appropriate container.
13. Label the container, including appropriate warnings, such as "Shake well before use," and, if necessary, "For external use only."

Worked Example (Specific Formulation)

• Page 30, Example of a Magnesium Trisilicate Mixture formulation with specific ingredient quantities
• Step-by-step instructions are included on different preparation stages using the master formula as a guide

External Use Suspensions

• Consider the appropriate suspending agent, such as tragacanth, bentonite, methylcellulose, or carbomer.

Inhalations

• Liquid products with volatile ingredients to contact respiratory linings
• Inhalations formulated as suspensions allow for volatile ingredient adsorption onto a carrier (diffusible solid), and the volatiles are then released and inhaled when suspended in hot water.

Lotions

• May be suspensions, solutions, or emulsions for external use only
• Applied directly to skin and used for soothing, cooling, drying, and protecting irritated skin.

Applications

• Suspensions or solutions or emulsions applied directly to the skin without a dressing

Packaging

• Packaging should follow solutions principles
• Oral uses should be in plain (smooth) amber bottles
• External uses should be in fluted amber bottles

Discard Dates

• Discard dates similar to pharmaceutical solutions, but with a shorter expiry time for suspensions lacking preservatives
• 2 weeks for freshly prepared, vegetable matter and infusion preparation
• 4 weeks for recently prepared suspensions
• 7-14 days for suspensions without preservatives, new, or ad hoc

Explore the vital role of suspensions in pharmaceutical compounding. This quiz covers their various applications, advantages, and disadvantages compared to solutions. Test your knowledge on the characteristics of oral suspensions as defined by the British Pharmacopoeia.