A mixture is a liquid preparation meant for oral administration in which medicament
are dissolved in a suitable vehicle. Generally, several dosages are dispensed in a bottle. In case, a bottle contain one dose it is called draught.
The mixtures are not prepared for a longer period because they are mainly prescribed for acute conditions such as cough, indigestion, diarrhoea, constipation etc.The mixtures should be extemporaneously prepared and supplied only for small number of doses which can be used up within a short period of time.
Classification of mixtures:
Mixtures are classified into
i. Simple mixtures containing soluble substances
ii. Mixtures containing diffusible solids
iii. Mixtures containing indiffusible solids
iv. Mixtures containing precipitate forming liquids
V. Mixtures containing slightly soluble liquids.
1. Simple mixtures:
Contains only soluble ingredients.
Eg: Carminative mixture, diarrhea and expectorant mixture.
2. Mixtures containing diffusible solids:
Diffusible solids are those which do not dissolve in water, but get mixed upon shaking, the powder drug is evenly diffused throughout the liquid for sufficient time to ensure uniform distribution in each dose. The commonly used diffusible drugs are.,
2. Magnesium carbonate (heavy or light)
3. Mixtures containing indiffusible solids:
Indiffusible solids 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 drugs in mixtures are.,
l Acetyl salicylic acid, benzoic acid
l Phenobarbitone, phenacetin.
The suspending agents use in this are.,
a) Compound tragacanth powder: In the proportion of 2g/100ml of the mixture
b) Tragacanth mucilage: In the proportion of 1/4th of the volume of the mixture.
4. Mixture containing precipitate forming liquids:
Liquid preparations containing resinous matter, when mixed with water, the resin is precipitated which may adhere to the sides of the bottle which will not re-diffuse upon shaking. To prevent this compound tragacanth powder or mucilage are used.
5. Mixture containing slightly soluble liquids:
The insoluble portion of slightly soluble liquids is not readily diffusible. So, a suspending agent such as compound tragacanth powder or mucilage are used.
6. Formulation of mixtures:
1. Vehicles – Water, aromatic water(camphor, chloroform, peppermint water),
2. Chemical stabilizers – Antioxidants are generally used like Ascorbic acid(0.1%)
3. Preservatives – containing diluted vegetable extract and flavouring agents are the source of bacteria and fungi in mixture.