The sources of contamination in pharmaceuticals arises from raw materials, processing containers, equipment, manufacturing environment, working personnel and packaging materials. These contaminants allow the growth of various microorganisms such as Salmonella species, Escherichia coli, Enterobacter species, Pseudomonas aeruginosa, Clostridium and Candida albicans which are undesirable in oral liquid preparations. The presence of a preservative will hinder the growth of microbes, thereby extending the shelf life of the product (Table 6.2). An ideal preservative should possess the following characteristics:
- It must be effective against a broad spectrum of microorganisms.
- It must be physically, chemically and microbiologically stable during the shelf life of the product.
- It must be nontoxic, nonsensitizing, adequately soluble, compatible with other formulation components and acceptable with respect to taste and odor at the concentrations used.
Table 6.2 Pharmaceutically Useful Preservatives and Their Concentration
| Preservative | Concentration (%) |
|---|---|
| Phenol | 0.2–0.5 |
| Chlorocresol | 0.05–0.1 |
| O-Phenyl phenol | 0.005–0.01 |
| Alkyl esters of para-hydroxy benzoic acid | 0.001–0.2 |
| (e.g., methyl and propyl paraben) | |
| Benzoic acid and its salts | 0.1–0.3 |
| Boric acid and its salts | 0.5–1.0 |
| Sorbic acid and its salts | 0.05–0.2 |
| Chlorobutanol | 0.5 |
| Benzyl alcohol | 1.0 |
| b-Phenylethyl alcohol | 0.2–1.0 |
| Thiomersal | 0.001–0.1 |
| Phenyl mercuric acetate and nitrate | 0.002–0.005 |
| Nitromersol | 0.001–0.1 |
| Benzalkonium chloride | 0.004–0.02 |
| Cetylpyridinium chloride | 0.01–0.02 |
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