Methylparabens antimicrobial activity

Parabens are approved for use in oral solution and suspensions at a concentration of 0.015% to 0.2% w/v. Due to their low solubility, the sodium salts of parabens are often used in aqueous formulations. The parabens are most effective in the pH range of 2 to 6, and their antimicrobial activity decreases with increasing pH. Additionally, they are very unstable at pH 8 or above in solution. Methyl paraben has also demonstrated incompatibility with sorbitol and may show some discoloration in the presence of iron. The absorption of methylparaben by plastics has been reported with the amount absorbed being dependent upon the type of plastic and vehicle. However, no absorption has been reported for low density polyethylene (LDPE) or high density polyethylene (HDPE) containers. Certain coloring agents such as yellow iron oxide, ultramarine blue, and aluminum silicate can extensively absorb ethyl paraben in simple aqueous systems, thus reducing its preservative efficacy. 

The antimicrobial activity of methylparaben and other para-bens is considerably reduced in the presence of nonionic surfactants, such as polysorbate 80, as a result of micelliza-tion. ° However, propylene glycol (10%) has been shown to potentiate the antimicrobial activity of the parabens in the presence of nonionic surfactants and prevents the interaction between methylparaben and polysorbate 80. ... 

Discoloration and/or precipitation occur with various substances, especially phenols, tannins, tars, and tarlike materials. The antimicrobial activity of paraben preservatives is reduced in the presence of polysorbates. See Methylparaben. 

In addition, 4-hydroxybenzoic add is widely used together with its alkyl esters (generally known as parabens) and salts. The most common are methyl-, ethyl-, propyl- and butyl- esters and are generally known as methylparaben, ethylparaben, etc. The antimicrobial activity of these chanicals increases as the carbon number of the alkyl chain increases, while, by contrast, their water solubility decreases in parallel. The antimicrobial activity of the individual esters is generally selective, so their mixtures offer powerful antimicrobial activity against an extremely broad spectrum of microorganisms This is the reason why a lot of cosmetics and skin care products are preserved with parabens both in Europe and the United States. 

In pharmaceutical analysis, the majority of matrix components (excipients) are present to improve manufacturing characteristics like bulk powder flow, tablet hardness, or to enhance tablet disintegration.12 Other excipients are present in a formulation to preserve the active pharmaceutical ingredient13 (antioxidant, for example) or to act as an antimicrobial agent14 (methylparaben, for example). Still other excipients may be present to increase the palatability of the formulation15 (flavors, for example). 

The most frequently used antimicrobials found in commercial shampoos are parabens, methylparaben and propylparaben. Mixtures of different preservatives provide broader protection against a wider spectrum of microorganisms and have been proven to be the most effective method to ensure product robustness [100], The level of preservative necessary depends on the composition of ingredients, total alcohol level, pH value, and water activity. 

---