A pharmaceutical mixture is a liquid dosage form intended for oral administration. Here drugs and other ingredients are dissolved or suspended in a suitable vehicle. This is the simplest and oldest form of liquid dosage form. Pharmaceutical mixtures are usually prepared extemporaneously by a compounding pharmacist for the treatment of acute conditions like cough, indigestion, constipation, diarrhea etc.
Mixtures are generally prepared and dispensed in a small number of doses and must be used within a specified time period. Draughts are also a type of pharmaceutical mixture which is dispensed as a single dose.
Read more about types liquid dosage forms
Now we can discuss some advantages and disadvantages of pharmaceutical mixtures
Advantages of pharmaceutical mixtures
- Easy for administration to all types of patients
- Medicines can be mixed with different types of solvents to make it acceptable for different patient categories.
- As it is prepared extemporaneously dosage can be adjusted for different patients.
- As it is liquid form patients can take their prescribed dose accurately
Disadvantages of pharmaceutical mixtures
- Physical and chemical stability will be less
- As it is prepared extemporaneously there are chances of variation in durg content and other effects.
- Preparations should be taken within a short duration of time
Types of pharmaceutical mixtures
There are mainly five types of pharmaceutical mixtures
- Simple mixture containing soluble substances
- Mixture containing diffusible solids
- Mixtures containing indiffusible solids
- Mixtures containing precipitate forming liquids
- Mixtures containing slightly soluble liquids
- Simple mixture containing soluble substances
Simple mixtures are prepared by dissolving drugs and other ingredients in a suitable vehicle. These mixtures only contains soluble ingredients so this can be easily prepared and dispensed
Examples are: carminative mixture, expectorant mixture etc.
- Mixture containing diffusible solids
Diffusible solids are those solids which are insoluble in water or required vehicles but they are miscible with it. These solids will stay evenly distributed for sufficient time upon shaking to ensure uniform distribution of drug in each dose.
Examples of diffusible drugs are bismuth carbonate, bismuth subnitrate, magnesium carbonate, light kaolin etc.
- Mixtures containing indiffusible solids
Indiffusible solids are those which are not soluble in water and also they will not stay evenly distributed for sufficient long time after shaking. So, in order to prepare mixtures with indiffusible solids we have to add a suspending agent or thickening agent like compound tragacanth powder or tragacanth mucilage.
Examples of indiffusible drugs are acetylsalicylic acid, quinine salicylate, calomel, phenacetin, benzoic acid etc.
- Mixtures containing precipitate forming liquids
There are certain liquid preparations which when mixed with water precipitates are formed. This is due to resinous matters contained in those preparations. These precipitated resins form large solids or adhere to the sides of the bottle.
In the preparation of mixtures using these preparations we have to add compound tragacanth powder or tragacanth mucilage. Also these precipitate forming liquid is added to the vehicle as a slow stream with constant stirring.
- Mixtures containing slightly soluble liquids
Slightly soluble liquids are not completely soluble and also their insoluble parts remain indiffusible in the vehicle. Here a suspending or thickening agent is added in the preparation.
Additives used in the formulation of pharmaceutical mixtures
Important additives used in the formulation of pharmaceutical mixtures are following
- Vehicles
Commonly used vehicles in formulation of mixtures are water, aromatic water and medicated vehicles.
If water is used as vehicle it must be purified or distilled water
Aromatic water also act as a flavoring agent
Medicated vehicles used include compound gentian infusion, orange peel infusion, infusion of senega etc
- Chemical stabilizers
Chemical stabilizers added to mixtures to improve stability of certain formulations which get easily oxidized up on storage or when mixed with other ingredients.
Examples include ascorbic acid which is added to ferrous sulfate mixture. Sodium metabisulfite added to sodium salicylate mixture etc.
- Coloring agents
Coloring agents are added to improve the appearance of a preparation. Coloring agents are rarely used in mixture formulation
- Flavoring agents
Commonly used flavoring agents are following
- Aromatic water
- Syrup of glycerol
- Liquid extracts of liquorice
- Lemon spirit
- Orange syrup
- Preservatives
Preservatives are added to a mixture to prevent any contamination of preparation by microbial growth. Examples of preservatives used in pharmaceutical mixture formulation are chloroform, benzoic acid etc.
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