RESUMO
Objective To prepare dl-tetrahydropalmatine (dl-THP) ethosomes (ETS) and elucidate their transdermal absorption properties. Methods Dl-tetrahydropalmatine ethosomes (dl-THP ETS) were prepared by ethanol injection combined with pH-gradient active drug-loading method. Their physicochemical properties including elasticity, vesicle size, morphology and entrapment efficiency were characterized. Franz diffusion cells were used to investigate the ex vivo skin permeation characteristics of the formulation with liposomes (LPS) and tinctures being used as reference preparations. Results According to a preferred formulation of dl-THP ETS [dl-THP 100 mg, vitamin E 1.3 mg, soybean lecithin 1 200 mg, cholesterol 120 mg, absolute ethanol 9 mL and citrate buffered saline (pH 3.0) 21 mL, 0.1 mol/L NaOH solution suitable quantity (to adjust the pH value to 5.5) ], the obtained dl-THP ETS had an elasticity index of (20.1 ± 1.1) mL, an average size of (85.8 ± 0.9) nm with a polydispersity index of (0.082 ± 0.003) and an entrapment efficiency of (81.7 ± 3.2)%. The cumulative permeated drug quantity per unit area (Qn) of dl-THP ETS in 24 h was (2 306.4 ± 592.3) μg/cm2 with no significant difference compared with the Qn of the LPS [(2 434.2 ± 564.4) μg/cm2] (P > 0.05) and about 4 times of that of the tincture [(633.1 ± 218.0) μg/cm2] (P < 0.05). And the averages of RSD of the Qn at each time point were (28.37 ± 10.9)% and (62.83 ± 44.1)% for the ETS and LPS, respectively, indicating that the Qn fluctuation among samples of the ETS was smaller than that of the LPS (P < 0.05). Average correlation coefficients of (0.968 ± 0.033) and (0.882 ± 0.078) (P < 0.05) were obtained for the ETS and LPS respectively when their 24 h permeation curves were fitted to linear relationship, indicating the permeation of the former was closer to zero-order kinetics than that of the latter. Conclusion The dl-THP ETS have a high elasticity, a suitable size, a high entrapment efficiency, and enhanced and stable percutaneous absorption in line with zero-order kinetics.