Microemulsion-based novel transdermal delivery system of tetramethylpyrazine: preparation and evaluation in vitro and in vivo

Figures & data

Figure 1 Pseudo-ternary phase diagram of microemulsion composed of isopropyl myristate, surfactant (Labrasol^®) and CoSurfactant (Plurol^® Oleique CC 497), Km = 3:1, and water. (A) O/W microemulsion zone; (B) and (C) W/O microemulsion zones.

Abbreviations: O/W, oil in water; W/O, water in oil.

Table 1 Uniform experimental design for microemulsion formulation optimization

Experiment	Factors
	X1 (weight ratio of oil, %)	X2 (weight ratio of the mixture of S and CoS, Km = 3, %)
1	6.0	38.0
2	7.0	56.0
3	8.0	32.0
4	9.0	50.0
5	10.0	30.0
6	11.0	44.0

Table 2 Compositions and drug loadings of formulations 1 to 6 of microemulsions

Formulation	Weight fractions of components (%, w/w)				TMP loading (%, w/w)	Azone (%, w/w)
	Labrasol^®	Plurol^® Oleique CC	IPM	Water
1	28.5	9.5	6.0	56.0
2	42.0	14.0	7.0	37.0
3	24.0	8.0	8.0	60.0	2.0	1.0
4	37.5	12.5	9.0	41.0
5	22.5	7.5	10.0	60.0
6	33.0	11.0	11.0	45.0

Abbreviations: IPM, isopropyl myristate; TMP, 2,3,5,6-tetramethylpyrazine.

Table 3 Characteristics of formulation 1 to formulation 6 and skin permeation parameters of TMP

Formulation	Characteristics of microemulsions				Skin permeation parameter
	Mean droplet size (nm)	PDI	Viscosity (mPa·S)	TMP solubility (mg/mL)	Flux (mg/cm^2/h)
1	51.47 ± 0.25	0.352 ± 0.015	34.0 ± 0.4	4.13	0.164 ± 0.022
2	95.04 ± 1.30	0.251 ± 0.015	53.2 ± 0.5	7.07	0.139 ± 0.004
3	45.02 ± 0.37	0.329 ± 0.003	30.2 ± 1.1	6.07	0.087 ± 0.012
4	78.21 ± 1.20	0.274 ± 0.004	45.0 ± 0.6	4.93	0.183 ± 0.019
5	42.74 ± 0.13	0.375 ± 0.011	30.2 ± 0.5	5.93	0.191 ± 0.023
6	66.64 ± 0.18	0.397 ± 0.002	33.3 ± 1.6	9.88	0.263 ± 0.027
TMP transdermal patch	–	–	–	–	0.009 ± 0.0007
TMP saturated solution	–	–	–	1.90	0.046 ± 0.005

Abbreviations: PDI, polydispersity index; TMP, 2,3,5,6-tetramethylpyrazine.

Figure 2 Transmission electron microscopy of tetramethylpyrazine-loaded microemulsion (formulation 6).

Figure 3 In vitro skin permeation profiles of TMP from formulations 1 to 6 of microemulsions, TMP loading was 2% (w/w), with TMP transdermal patch and TMP saturated solution as controls. The weight fractions of components in formulations 1 to 6 were 6.0, 7.0, 8.0, 9.0, 10.0 and 11.0 for IPM; 28.5, 42.0, 24.0, 37.5, 22.5, and 33.0 for Labrasol^®; and 9.5, 14.0, 8.0, 12.5, 7.5, and 11.0 for Plurol^® Oleique CC 497, respectively.

Abbreviations: IPM, isopropyl myristate; TMP, 2,3,5,6-tetramethylpyrazine.

Table 4 Skin permeation parameters in vitro and characteristics of formulation 6 with different drug loadings

Drug loading (%, w/w)	Saturated amount of TMP in the donor compartment (mg)	Residue amount of TMP in the donor compartment after 24 h (mg)	Skin flux of TMP (mg/cm^2/h)
0.6	29.64	15.72 ± 1.24	0.056 ± 0.007
1.0	29.64	25.86 ± 3.58	0.103 ± 0.014
2.0	29.64	49.10 ± 4.96	0.263 ± 0.027

Abbreviation: TMP, 2,3,5,6-tetramethylpyrazine.

Figure 4 In vitro skin or EVA membrane permeation profiles of TMP from formulation 6 of microemulsions 1.0%-EVA: EVA membrane permeation profile of TMP from formulation 6, with TMP loading being 1.0% (w/w); 0.6%, 1.0%, and 2.0%: rat skin permeation profiles of TMP from formulation 6, with TMP loadings being 0.6%, 1.0%, and 2.0% (w/w), respectively.

Abbreviations: EVA, ethylene vinyl acetate; IPM, isopropyl myristate; TMP, 2,3,5,6-tetramethylpyrazine.

Table 5 Pharmacokinetic parameters of TMP after a single-dose transdermal administration of TMP-O/W-EVA-TTS (10 mg of TMP in 6 cm²) to each rat in group A (n = 6) and TMP transdermal patch (10 mg of TMP in 6 cm²) to each rat in group B (n = 6)

Parameters	TMP-O/W-EVA-TTS	TMP transdermal patch
Cmax (μg/mL)	0.49 ± 0.09	0.29 ± 0.07
Tmax (h)	12.00	2.67 ± 0.58
AUC (h*μg/mL)	9.0495 ± 1.2368**	2.579 ± 0.723
MRT (h)	12.1939 ± 0.3712**	7.886 ± 0.351
Cl (L/h)	0.676 ± 0.207*	3.324 ± 0.997
Relative bioavailability (%)	350.89

Notes: * and ** represent P < 0.05 and P < 0.01, respectively, compared with TMP transdermal patch.

Abbreviations: AUC, area under the curve; Cl, clearance; MRT, mean residence time; TMP, 2,3,5,6-tetramethylpyrazine; TMP-O/W-EVA-TTS, tetramethylpyrazineoil dispersed in water-ethylene vinyl acetate-transdermal therapeutic system.

Figure 5 Mean concentrations of TMP in rat plasma versus time profiles from TMP-O/W-EVA-TTS and TMP transdermal patch.

Abbreviations: TMP, 2,3,5,6-tetramethylpyrazine; TMP-O/W-EVA-TTS, tetramethylpyrazine-oil dispersed in water-ethylene vinyl acetate-transdermal therapeutic system.

Figure 6 Mean concentrations of TMP in rat brain homogenate versus time profiles from TMP-O/W-EVA-TTS and TMP transdermal patch.

Abbreviation: TMP, 2,3,5,6-tetramethylpyrazine; TMP-O/W-EVA-TTS, tetramethylpyrazine-oil dispersed in water-ethylene vinyl acetate-transdermal therapeutic system.