Transdermal absorption enhancing effect of the essential oil of Rosmarinus officinalis on percutaneous absorption of Na diclofenac from topical gel

Context: Rosemary essential oil has been used topically for several purposes (analgesic, anti acne, and anti-inflammatory) in Iranian traditional medicine. Objectives: This investigation aimed to study the effect of essential oil of Rosmarinus officinalis L. (Lamiaceae) on the transdermal absorption of Na diclofenac from topical gel. Material and methods: Diclofenac sodium topical gel was prepared with HPMC K4M and Carbopol 934P as a gelling agent, and several vehicles. The most stable gel was chosen and enhancing effects of the essential oil with different concentrations (0.1, 0.5, and 1.0% w/w) on the permeation of diclofenac were evaluated. The anti-nociceptive effect of preparations was evaluated based on the formalin and tail flick tests in mice. Results: The major constituents of the essential oil were 1,8-cineol (15.96%), alpha-pinene (13.38%), camphor (7.87%), bornyl acetate (6.54%), verbenone (5.82%), borneol (5.23%), camphene (4.96%), and (E)-caryophyllene (3.8%). Topical diclofenac containing 0.5% essential oil showed more analgesic effect after 25, 30, and 35 min (p < 0.001) than the reference drug in the tail flick test. The analgesic effect of preparation containing 1% essential oil was more than reference gel after 15 min (p < 0.05). This difference was observed after 20, 25, 30, 35, and 40 min (p < 0.001) too. Rosemary essential oil 1% promoted analgesic effect of drug in comparison with diclofenac gel in the formalin early phase (p < 0.05). The enhancing effect of rosemary was observed in 0.5 and 1% concentration (p < 0.05 and p < 0.001, respectively) in the late phase. Conclusion: This study proved the enhancing effect of 0.5 and 1% of rosemary essential oil on diclofenac percutaneous absorption.