Effect of different pharmaceutical vehicles on antimicrobial action of essential oils

The aim of present work was to investigate the effect of different pharmaceutical vehicles on antimicrobial action of essential oils. Based on preliminary antimicrobial studies of essential oils from Patchouli (P), Geranium (G) and Coriander (R) in pure form as well as in mixture, three combinations (1:1) of oils were prepared and designated as P+G, G+C and C+P. Incorporating these combination of oils as active pharmaceutical ingredient (3% w/w), a variety of bases viz. base 1 and base 2 (hydrophilic ointment), base 3 (hydrophobic ointment), base 4 and base 5 (O/W emulsion), base 6 (light-liquid paraffin) and base 7 (Tween 80) were formulated and subjected to agar diffusion assay against a wide spectrum of gram positive and gram negative bacteria. For comparison a popular marketed antiseptic cream was also evaluated for antimicrobial activity. It was observed that base 1 showed promising bactericidal action (4–13mm) followed by marketed cream (2–8mm) and base 2 (1–6mm). Base 5 and base 6 exhibited bacteriostatic action whereas base 3, base 4 and base 7 did not show any antimicrobial activity. Divergence in antimicrobial action of essential oils into different pharmaceutical vehicles may be attributed to the release characteristic of oil to the outer environment (agar medium). Hydrophilic ointment facilitates release of oils in comparison to hydrophobic ointment base resulting into bactericidal action, whereas emulsification and solubilisation of essential oil caused diminished antimicrobial activity. Chemical binding of non-ionic surfactant Tween 80 with active ingredient may be responsible for loss of antimicrobial activity.