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 and glycerol was investigated. The co-solvents at 3 M concentrations increased the solubility of parabens. The increased solubility of parabens in the co-solvents over their aqueous solubility was associated with increased antibacterial activity. The extent of this effect was different for different co-solvents, and increased with increasing hydrophobicity of the co-solvent. Two potentially useful paraben/co-solvent combinations were identified and their activity compared with two commercially used paraben combinations. Further studies indicate that addition of co-solvents to oil/water systems is associated with reduced partitioning of the parabens into the oil phase which may be associated with increased preservative activity within an emulsion formulation.