1) Vehicles
2) Adjuvants
Solubilising agent
Stabilizers:
Buffering agents
Antibacterial agents:
Chelating agents:
Suspending,
Emulsifying and wetting agents:
Tonicity factors
1) Vehicles :
There are two types of vehicle which are commonly used for preparation of parental
i) Aqueous vehicle – Water for injection is used which is sterile water free from volatile
and non volatile impurities and also from pyrogens
ii)Non aqueous vehicle –Commonly used non aqueous vehicle are oils and alcohols
Fixed oil such as arachis oil, cotton seed oil, almond oil and sesame oil are used as vehicle
Dimercaprol injection where arachis oil is used as vehicle
Ethyl alcohol is used as vehicle for preparation of hydrocortisone injection
2)Adjuvants:
These substances are added to increase the stability or quality of the product. The
following adjuvants are commonly used in preparing stable parenteral preparations
Solubilising agents:
These are used to increase the solubility of drugs which are slightly soluble in water. The
solubility of drug is increased by using surface active agent like tweens and polysorbates by
using co-solvents.
Stabilizers:
The drugs in the form of solutions are more liable to deteriorate due to oxidation and
hydrolysis. The stabilizers are added in the formulation to prevent this. The oxidation can
be prevented by adding a suitable antioxidant such as thiourea, ascorbic acid or the product
is sealed in an atmosphere of nitrogen. Hydrolysis can be prevented by using a non-aqueous
vehicle or by adjusting pH.
Buffering agentsThe degradation of the preparation which is due to change in pH can be prevented by
adding a suitable buffer to maintain the desired pH. For e.g.Citric acid and sodium citrate,
acetic acid and sodium acetate.
Preservatives.
These substances are added in adequate quantity to prevent the growth of microorganism during storage.
Chelating agents:
Chelating agents such as EDTA and its salts, sodium or potassium salts of citric acid are
added in the formulation, to chelate the metallic ions present in formulation.
Suspending,Emulsifying and wetting agents:
The suspending agents are used to improve the viscosity and to suspend the particles for a
long time. Methyl cellulose, carboxymethyl cellulose, gelatin and acacia are commo0nly
used. Emulsifying agents are used in sterile emulsion.eg-Lecithin. The wetting agents are
used to reduce the interfacial tension between the solid particles and the liquid so as to
prevent formation of lumps.
Tonicity factors:
Parenteral preparation should be isotonic with blood plasma or other body fluids. The
isotonicity of solution may be adjusted by adding Sodium chloride, dextrose etc