Various types of excipients are added in the medicinal products to serve different purpose for example to enhance stability/ absorption, consumption, administration, aesthetic appearance etc. Preservatives are substances (natural or chemical) that are added to pharmaceutical products to prevent any kind of physical, chemical or biological changes.
IDEAL PROPERTIES OF A PRESERVATIVE:
CLASSIFICATION OF PRESERVATIVES:
Based on Mechanism of Action
- Antimicrobial Agents
- Chelating Agents
Based on Source
- Natural: Obtained through natural source. Example: Salt, Lemon etc
- Synthetic: Man made or chemically synthesized. Example: Benzoates etc
- Antioxidants: They are self reducing agents that oxidize themselves and prevent oxidation of the components that are sensitive to oxygen. For example: Vitamin C, Vitamin E, BHA (butylatedhydroxyanisole), BHT (Butylatedhydroxytoulene), propyl gallate etc. They make an excellent guard against deterioration which considers two main factors oxygen and sunlight.
- Antimicrobial agents: These agents act against microorganisms by affecting the various cellular portions of microbial cell and thereby inhibiting their growth. Cell wall, cytoplasmic membrane and cytoplasm are such portions of microbial cell wall that are mostly targeted by the preservatives. The factors that effect in choosing the antimicrobial preservative include: preservative dose, its effect on active ingredient and range of antimicrobial functionality. Some examples are phenol, parabens, aryl and alkyl acids etc.
- Chelating Agents: They term chelate derived from greek word “chele” which indicates “Crab’s claw”. In this the ligand molecule binds through donor groups and make a type of ring thus forming a complex with the pharmaceutical ingredient thus protecting it from any deterioration. For example EDTA, Citric acid etc.
SOME COMMON PRESERVATIVES USED IN PHARMACEUTICAL PREPARATIONS WITH THEIR CONCENTRATIONS:
|Preservative||Class||Concentration in preparations (in %)|
|Oral Liquid||Parenterals||Opthalmic/ Nasal||Ointments and creams|
|Methyl Paraben||Amino aryl acid esters||0.25||0.01-0.5||0.1||0.001-0.2|
|Benzyl Alcohol||Alkyl/ aryl alcohols||3.0||0.5-10|
|Benzoic acid||Alkyl/aryl acids||0.1-0.2|
|Benzylkonium Chloride||Quatenary Ammonium Compounds||0.002-0.02||0.01||0.004-0.02||0.01|