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.
