THE EFFECT OF COSOLVENTS ON THE ANTIBACTERIAL ACTIVITY OF PARABEN PRESERVATIVES

The solubility of methyl and propyl p-hydroxybenzoate esters (parabens ) in 3 M concentrations of the co-solvents ethanol, propylene glycol a nd glycerol was investigated. The co-solvents at 3 M concentrations in creased the solubility of parabens. The increased solubility of parabe ns in the co-solvents over their aqueous solubility was associated wit h increased antibacterial activity. The extent of this effect was diff erent for different co-solvents, and increased with increasing hydroph obicity of the co-solvent. Two potentially useful paraben/co-solvent c ombinations were identified and their activity compared with two comme rcially used paraben combinations. Further studies indicate that addit ion of co-solvents to oil/water systems is associated with reduced par titioning of the parabens into the oil phase which may be associated w ith increased preservative activity within an emulsion formulation.