Learning Objective

• Types of physical incompatibility

The following are the various types of mixtures with physical incompatibilities:

1. Immiscibility Example:Castor oil15 mlWater (q.s.)100 ml Incompatibility: Oil and water do not mix.Remedy: Carry out emulsification by the addition of an emulsifying agent, by the use of primary emulsion formula.
2. Insolubility Example:Phenacetin3.33 gCaffeine1.11 gOrange syrup13.3 mlWater (q.s.)100 ml Incompatibility: Phenacetin is an indiffusible solid.Remedy: Compound powder of tragacanth (2 g/100 ml of finished product) or tragacanth mucilage is used as a suspending agent.It increases the viscosity of the preparation and helps to maintain a uniform distribution of the insoluble substances for sufficiently long time after shaking the bottle in order to facilitate removal of a uniform dose.
3. LiquefactionExample:Menthol130 mgCamphor260 mgLight magnesium oxide390 mg Incompatibility: When two organic substances having a low melting point are brought into physical contact with each other, they liquefy due to the formation of a new substance that has a melting point below room temperature. The reason for this change is that each ingredient acts as an impurity for the other, thereby lowering their melting point. Such substances are called eutectic substances.Example: Menthol, camphor, thymol and ammonium chlorideRemedy: Eutectic powders may be dispensed in following two ways:
   • They can be dispensed as a separate set of powders with directions that one set of each powder may be taken as a single dose.
   • They can also be dispensed by adding a high melting point inert substance such as kaolin, starch, lactose or light magnesium oxide. These substances act as adsorbents and prevent liquefaction.