Pastes definition and it's despencing procedure


Definition: pastes 
  Pastes may be defined as the semi-solid preparations ment for external  application onto skin to form a protective coating over the skin.
Pastes are less greasy when compared to ointments but very thick and stiff because of their high solid content.
     
       Preparation :  pastes are prepared  by irritation and fusion method, which are same as used in the preparation of ointments. 
   
        1.Trituration method : 
The trituration method is used when the base is soft and the solid medicament is insoluble in the base. 
The method may be as follows, 
1.Accurately weigh the required amount of the solid medicament and finely powder it. Also weigh the amount of base. 
2.triturate the solid medicament in small  amount of base with a spatula on a plain slab, until a uniform  and homogeneous product is formed.
3.mix the remaining amount of the base in the homogeneous product to form a uniform mixture. 
4.add the liquid ingredients, if present. 
If large quantities of liquid ingredients are to be added, then the slab method cannot be used. Hence, motor and pestle are required for mixing of large quantities of liquids. 

 2. Fusion method :
  The fusion method is used when large number of solid ingredients having different melting points are to be incorporated into the base. 
The method involves, 
 1.The solid ingredients having highest melting point is to be melted first.
The remaining solid are method in the decreasing order of their melting point. 
2.The medicament is then slowly incorporated into the melted mass with constant stirring  until a uniform and a homogeneous product is formed. 
3.If any liquid ingredient are to be added, then they are also heated to same temperature as that of melted base and then mixed with constant stirring. 
4.Rapid cooling and vigorous stirring should be avoided else it may lead to entrapment of air.
5.The preparation must be strained through a muslin cloth in order to remove any dust or foreign particles. 
6.Transfer into a suitable container ,label and dispense. 

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