Nanoemulsion: for improved oral delivery of repaglinide

Figures & data

Table 1. Treatment schedules of repaglinide formulations for antidiabetic activity in SD rats.

Groups	Drugs	Treatment schedule
I	Normal control	Normal saline 10 ml/kg p.o. single dose
II	Diabetic control	Normal saline 10 ml/kg p.o. single dose + STZ (100 µg/g i.p.)
III	Standard	Conventional formulation of repaglinide 2 mg/kg p.o. single dose given to diabetic rats
IV	R1 (RN13)	Optimized nanoemulsion of repaglinide 0.5 mg/kg p.o. single dose given to diabetic rats
V	R2 (RN13)	Optimized nanoemulsion of repaglinide 1.0 mg/kg p.o. single dose given to diabetic rats
VI	R3 (RN13)	Optimized nanoemulsion of repaglinide 2 mg/kg p.o. single dose given to diabetic rats

Figure 1. Bar diagram showing the highest solubility of repaglinide in sefsol 218. HCO, hydrogenated castor oil; CP90, Caproyl 90; SF218, Sefsol 218; T80, Tween-80; T20, Tween-20, TCN, triacetin; LBF, labrafac; LRG, lauroglycol; IPM, isopropyl myristate; OA, oleic acid; S:T 80 (2:1), Sefsol:Tween-80 (2:1); S:T 80 (1:1), Sefsol:Tween-80 (1:1).

Figure 2. Pseudo-ternary phase diagrams [Smix ratio = 1:0 (A), 1:1 (B), 2:1 (C),3:1 (D), 1:2 (E) and 1:3 (F)]. The dotted area represents o/w nanoemulsion region.

Table 2. Observations for thermodynamic stability study and dispersibility test of repaglinide nanoemulsion formulations.

					Observations based on themodynamic stability test			Observations based on dispersibility test
Formulation	Smix ratio	% Smix	% Oil	% Water	HC^a	Cent^b	F^c	Distilled H2O	0.1 N HCl	Inference
RN 1	1:0	20	5	75	x	–	–	–	–	Failed
RN 2		25	10	65	x	–	–	–	–	Failed
RN 3		25	5	70	x	–	–	–	–	Failed
RN 4		30	20	50	x	–	–	B	B	Failed
RN 5		30	10	60	√	√	√	C	C	Failed
RN 6		30	5	65	√	√	√	A	A	Passed
RN 7	1:1	35	15	50	√	√	x	B	B	Failed
RN 8		35	10	55	√	√	x	C	C	Failed
RN 9		35	5	60	√	√	x	C	C	Failed
RN 10		40	10	50	√	x	–	B	B	Failed
RN 11		40	5	55	√	x	–	B	B	Failed
RN 12		45	5	50	√	√	√	A	A	Passed
RN 13	2:1	30	5	65	√	√	√	A	A	Passed
RN 14		35	5	60	√	x	–	B	B	Failed
RN 15		40	10	50	√	x	–	B	B	Failed
RN 16		40	5	55	√	√	√	A	A	Passed
RN 17		45	5	50	√	√	√	A	A	Passed
RN 18	3:1	40	5	55	√	√	√	A	A	Passed
RN 19		40	10	50	√	√	√	A	A	Passed
RN 20		40	10	50	√	√	x	C	C	Failed
RN 21	1:2	30	5	65	√	√	x	B	B	Failed
RN 22		30	10	60	√	√	x	B	B	Failed
RN 23		35	5	60	√	√	x	B	B	Failed
RN 24		40	5	55	√	√	x	C	C	Failed
RN 25		40	10	50	√	√	x	D	D	Failed
RN 26		45	5	50	√	√	x	B	B	Failed
RN 27	1:3	30	20	50	x	–	–	D	D	Failed
RN 28		35	15	50	x	–	–	E	E	Failed
RN 29		40	10	50	√	√	x	E	E	Failed
RN 30		45	5	50	√	√	x	D	D	Failed

^aHeating–cooling cycle.

^bCentrifugation.

^cFreeze–thaw cycle.

Figure 3. (A) Transmission electron microscopic positive image of optimized repaglinide nanoemulsion (Formulation RN13). (B) Size distribution by intensity of optimized nanoemulsion (Formulation RN13).

Table 3. Droplet size, polydispersity index, viscosity, refractive index and electrical conductivity of selected repaglinide nanoemulsion formulations.

Formulation code	Droplet size ± SD (nm)^a	Polydispersity index^a ± SD	Viscosity ± SD (cps)^a	Refractive index ± SD^a	Conductivity (μS/cm) ± SD^a
RN 12	92.18 ± 8.31	0.214 ± 0.013	23.195 ± 0.342	1.6852 ± 0.008	527.106 ± 2.125
RN 13	76.23 ± 4.14	0.183 ± 0.011	21.447 ± 0.215	1.6605 ± 0.004	512.413 ± 3.157
RN 16	89.75 ± 6. 43	0.195 ± 0.014	22.412 ± 0.435	1.6962 ± 0.008	458.416 ± 4.685
RN 17	91.24 ± 11.82	0.229 ± 0.016	21.984 ± 0.463	1.6756 ± 0.005	403.213 ± 1.181
RN 18	96.19 ± 14. 97	0.407 ± 0.013	23.056 ± 0.216	1.7912 ± 0.007	452.415 ± 1.105
RN 19	97.15 ± 9.16	0.198 ± 0.017	23.857 ± 0.541	1.8502 ± 0.008	501.183 ± 5.764

^aMean ± SD, n = 3.

Figure 4. Comparative in vitro release profile of different formulations of repaglinide. All the values were expressed in mean ± SD (n = 3).

Table 4. Effects of repaglinide nanoemulsion on glucose level in the control and experimental groups of rat.

Time (h)	Normal control (NC)	Diabetic control (DC)	CF	R1	R2	R3
0	85.64 ± 4.88	305.24 ± 21.09*	304.40 ± 20.73*	301.73 ± 12.53*	302.32 ± 11.21*	309.63 ± 15.21*
2	84.93 ± 3.99	305.84 ± 20.95*	184.98 ± 11.32^## (39%)	229.84 ± 6.65^# (24%)	192.11 ± 16.18^## (36%)	189.00 ± 16.50^## (39%)
8	86.13 ± 4.79	306.51 ± 39.18*	110.69 ± 7.43^## (63%)	186.50 ± 23.54^# (38%)	99.92 ± 8.68^## (67%)	99.27 ± 7.14^## (68%)
12	84.28 ± 3.47	313.19 ± 20.25*	109.99 ± 7.92^## (64%)	219.12 ± 35.30^# (27%)	100.18 ± 8.47^## (67%)	100.36 ± 9.52^## (68%)
24	83.41 ± 4.31	323.60 ± 23.93*	187.97 ± 11.05^## (38%)	283.51 ± 31.70 ^ns(6%)	177.90 ± 9.16^## (41%)	181.93 ± 9.61^## (41%)

Mean ± SEM, n = 6.

*p < 0.001 considered more significant, when compared with NC, ^#p < 0.01 and ^##p < 0.001 considered significant, when compared with DC, p > 0.05 considered non-significant (ns), when compared with DC.

%, percentage reduction in blood glucose level; CF, conventional formulation (2 mg/kg); R1, R2 and R3, Nanoemulsion 0.5 mg/kg, 1 mg/kg and 2 mg/kg, respectively.