• Mixtures containing indiffusible soilds :- Indiffusible soilds are those solids which are not soluble in water and do not remain uniformly distributed in the vehicle for sufficiently long time. Therefore,to suspend the drug, suspending agents are added. The commonly used Indiffusible drug in mixture form are acetylsalicylic acid, quinine salicylate, calomel, phenacetin, benzoic acid, phenobarbital etc.
• The suspending agents which are commonly used in mixture containing indiffusible soilds are :-
• Compound tragacanth powder :- In the proportion of 2g/100 ml of the mixture.
• Tragacanth mucilage :- In the proportion of ¼ of the volume of the mixture.
• Compound tragacanth powder is used when the vehicle is other than water or chloroform Water but tragacanth mucilage is used when the vehicle is water or chloroform Water.
• Method of dispensing (using compound tragacanth powder)
1. Finely powder Indiffusible soilds. Add any soluble or diffusible solids and compound tragacanth powder. Mix them uniformly.
2. Measure about ¾ of the vehicle. Triturate the powder with a portion of it until a smooth cream is formed. Then add remainder of the vehicle
3. Examination the contents of the preparation. If any foreign particle is visible pass the contents through the muslin cloth. Rinse the mortar with little of vehicle.
4. Add any liquid ingredient if present and transfer the mixture into a measure.
5. Add more of the vehicle to produce the required volume.
6. Transfer the mixture into the bottle. Then thoroughly clean the bottle. Attach the label with a direction “ shake the bottle well before use” Dispense the bottle.
Method of dispensing (using tragacanth mucilage)
1. Finely powder the Indiffusible soilds. Add any soluble or diffusible solids. Mix them uniformly. Triturate the material with tragacanth mucilage to form a smooth cream. Then gradually dilute with ½ of the vehicle. The product will thus measure about ¾ of the finished volume.
2. Step 3,4,5,6 are the same aa described above in compound tragacanth powder method.
• Mixture containing precipitate forming liquid :-
• Certain liquid preparation contain resinous matter, when mixed with water, the resin is precipitated which may adhere to the sides of the bottle or form a clotted precipitate which will not re- diffuse upon shaking. To prevent this compound tragacanth powder or tragacanth mucilage are used.
• Mixture containing slightly soluble liquids :-
• The insoluble portion of slightly soluble liquids is not readily diffusible. So a suspending agent is needed to dispense such mixture.
• Compound tragacanth powder and tragacanth mucilage are used in the same proportion as discussed in mixture containing indiffusible soilds.
• Formulation of mixtures
1. Vehicle :- the vehicle commonly used for the preparation of mixture are
A. Water :- Purified water should be used for the preparation of mixture. The mixture should never be prepared with potable water because it contains volatile and non volatile impurities which may produce undesirable change in the medicines dissolved in it.
B. Aromatic water :- These are saturated solution of volatile oil and volatile substance in purified water. Aromatic water is mainly used for its flavouring properties. Some of the aromatic water are also having carminative and preservative action.
C. Medicated Vehicle :- Sometimes a vehicle with definite therapeutic activities is prescribed. For example compound compound gentian infusion, orange peel infusion and infusion of senega are used as vehicle preparing mixture. These infusion are prepared by diluting one volume of concentration infusion with seven volume of purified water.
2. Adjunct :- The following adjunct are generally used to improve the stability, colour and flavour of the mixture :-
• Chemical stabilisers :- certain chemical having anti oxidant or reducing properties are used to improve the chemical stability of the mixture. For example ascorbic acid (0.1%) is prescribed in ferrous sulphate Mixture to prevent oxidation of ferrous to ferric ions. The ferric salts are relatively ineffective in haemoglobin formation. Similarly sodium metabisulphate is included in Mixture containing sodium salicylate to prevent the darkness of Mixture due to atmospheric oxidation.
• Colouring agent :- No special colouring agent are added but many mixture contain coloured medicament.
• Flavouring agents :- The following flavouring agents are commonly used in mixture
A. Aromatic water such as anise water.
B. Syrup and glycerol for sweetening children preparation.
C. Liquid extract of liquorice to mask the saline taste of certain Mixture.
D. Spirit lemon to cover the taste of alkaline citrate.
E. Orange syrup and compound orange spirit to mask the metallic and astringent taste of iron salts in paediatric mixture.
• Preservatives :- Diluted vegetables extract and flavouring agent are the source of growth of bacteria and fungi in mixture. Hence chloroform (0.25% v/v) and benzoic acid (0.1w/v) is used to preserve such mixture.
3. Storage of mixture :- Mixture are dispensed in plain glass bottle with uniform internal diameter. These bottle are available in three different sizes to supply mixture of 60 ml , 120 ml , and 240 ml. The mixture should be dispensed and supplied to the patient for not more than three days to prevent deterioration. The bottle should be fitted with a suitable cork which will ensure its easy removal
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