PRESERVATIVES

Preservatives are substances added to various pharmaceutical dosage forms and cosmetic preparations to prevent or inhibit microbial growth. An ideal preservative would be effective at low concentrations against all possible micro-organism, be non- toxic and compatible with other constituent of the preparation and be stable for the shelf-life of the preparation.

CLASSIFICATION Preservatives can be classified as i) Acids: eg. Benzoic acid, Sorbic acids, Boric acids, ii) Esters: eg. Methylparaben, Ethylparaben, Propylparaben, Butylparaben, Sodium benzoate, Sodium propionate, Potassium sorbate. iii) Alcohols: eg. Chlorobutanol, Benzyl alcohol, Phenyl ethyl alcohol. iv) Phenols: eg. Phenol, Chlorocresol, o-Phenyl phenol. v) Mercurial compounds: eg. Thiomersal, Nitromersol, Phenylmercuric nitrate, Phenylmercuric acetate. vi) Quaternary ammonium compounds: eg. Benzalkonium chloride, Cetyl pyridinium chloride. Benzoic acid

COOH

Benzoic acid

Use: It is used as a food preservative, it inhibit the growth of mould, yeast and some bacteria. It is also used externally as antiseptic.

Boric acid It is a weak acid also called as ortho boric acid. It is a colorless crystal, soluble in water. H3BO3 Use: It is used as antiseptic, insecticide and flame retardant. 1

Methylparaben It is a white crystalline powder, characteristic odor, freely soluble in water and alcohol, slightly soluble in non-polar organic solvent.

COOCH3

OH Methyl - p- hydroxy benzoate Use: It is used as antiseptic and preservative in various pharmaceutical preparations. It is also used in cosmetic preparations containing vegetable and animal fats and oils that are susceptible to decomposition. Ethylparaben It is a white crystalline powder, slightly soluble in water, but soluble in alcohol and most of the organic solvents.

H3CH2COOC OH

Ethyl - p - hydroxy benzoate

Use: It is used as preservative and food additive.

Sodium benzoate It is a white crystalline solid, soluble in water and alcohol.

COO Na

Synthesis

2

COOH COO Na

+ NaOH - H2O

Benzoic acid Sodium benzoate Use: It is used extensively as food and pharmaceutical preservatives. It is not a bactericidal, only a bacteriostatic agent. It also possesses fungistatic activity.

Alcohols

Chloro butanol

Cl - CH2 - CH2 - CH2 - CH2 - OH 4 - Chloro - 1 - hydroxybutane

Use: It is used as preservative and bacteriostatic agent.

Benzyl alcohol

CH2OH

Use: It is used as bacteriostatic preservative. Mercurial Compounds Phenylmercuric nitrate

Hg.O.NO2

Use: It is used as bacterial preservative in pharmaceutical preparation and also used as topical antiseptic. 3