Maximizing the encapsulation efficiency and the bioavailability of controlled-release cetirizine microspheres using Draper–Lin small composite design

Figures & data

Table 1 Design matrix including investigated process variables with their levels

Batch number	X1	X2		X3	X4
1	20.0	6.45		3.318	10.0
2	36.818	6.45		5.0	10.0
3	20.0	6.45		5.0	1.591
4	30.0	4.3		4.0	15.0
5	10.0	8.6		4.0	15.0
6	20.0	2.834		5.0	10.0
7	10.0	4.3		6.0	5.0
8	10.0	4.3		4.0	5.0
9	20.0	10.066		5.0	10.0
10	20.0	6.45		5.0	18.409
11	30.0	4.3		6.0	15.0
12	30.0	8.6		4.0	5.0
13	20.0	6.45		6.682	10.0
14	20.0	6.45		5.0	10.0
15	10.0	8.6		6.0	15.0
16	20.0	6.45		5.0	10.0
17	3.182	6.45		5.0	10.0
18	30.0	8.6		6.0	5.0
Variable level	Lower extreme (−1.68)	Low (−1)	Medium (0)	High (1)	Higher extreme (1.68)
ERL loading (%, w/w) (X1)	3.182	10	20	30	36.818
Emulsifier HLB (X2)	2.834	4.3	6.45	8.6	10.066
Talc percentage (%, w/v) (X3)	3.318	4	5	6	6.682
Dispersed phase volume (mL) (X4)	1.591	5	10	15	18.409

Abbreviations: HLB, hydrophilic lipophilic balance; ERL, Eudragit RLPO.

Figure 1 Scanning electron photomicrographs of the optimized CTZ microspheres at (A) ×200 magnification, (B) ×300 magnification, (C) ×450 magnification, and (D) ×750 magnification.

Abbreviation: CTZ, cetirizine hydrochloride.

Table 2 Observed values of responses (Y₁–Y₇) for 18 formulations of CTZ-loaded polymethacrylate microspheres

Batch number	Particle sizea (Y1), µm	Angle of reposea (Y2),°	Production yieldb (Y3), %	Encapsulation efficiency b (Y4), %	Loading capacityb (Y5), %	Initial releasea (Y6), %	T85%a (Y7), h
1	330±1.45	18.5±0.04	78.7±1.31	71.4±0.93	8.7±0.44	26.15±0.74	13.19±0.41
2	291±1.24	19.8±0.11	80.7±1.14	72.7±1.35	9.7±0.39	35.19±1.25	9.14±0.09
3	283±1.75	20.1±0.54	84.3±1.33	77.2±1.43	11.5±0.19	27.45±0.15	13.25±0.24
4	239±1.04	21.2±0.24	67.8±0.71	63.4±0.83	7.9±0.21	32.14±0.34	9.78±0.21
5	247±2.15	21.3±0.13	71.2±1.01	66.5±1.11	8.6±0.08	18.14±0.09	16.65±0.53
6	223±0.45	23.7±0.09	86.4±1.03	67.3±1.32	8.7±0.14	24.32±0.39	12.98±0.14
7	245±0.96	29.8±0.15	97.5±2.72	84.3±1.03	13.4±0.22	17.33±0.65	16.15±0.32
8	268±1.54	20.3±0.07	90.3±1.94	79.5±2.43	11.8±0.10	17.54±0.54	17.31±0.85
9	231±2.15	23.9±0.24	82.4±1.55	75.1±1.41	10.8±0.25	30.15±1.12	14.25±0.71
10	197±1.31	27.6±0.17	63.9±0.84	51.6±0.95	6.8±0.13	27.15±0.34	13.09±0.92
11	96±0.84	34.5±0.06	71.5±1.25	61.6±1.52	7.3±0.23	33.45±1.37	10.33±1.04
12	275±1.26	18.5±0.15	93.7±3.33	81.9±2.24	12.6±0.09	33.92±2.09	9.25±0.44
13	87±0.79	33.4±0.26	81.7±1.41	74.3±2.06	10.7±0.15	28.14±0.84	13.87±0.65
14	224±1.57	25.3±0.38	82.4±2.11	73.9±3.11	9.8±0.12	29.18±0.47	14.52±1.54
15	110±2.23	31.7±0.23	73.9±1.23	67.8±1.25	9.1±0.08	19.72±0.26	16.42±2.06
16	219±1.91	26.1±0.08	79.8±2.03	73.7±2.13	9.9±0.17	28.77±0.75	14.01±1.39
17	210±2.32	24.8±0.19	83.4±1.68	72.7±1.72	9.7±0.09	15.57±0.64	25.35±3.53
18	256±3.09	30.3±0.14	95.6±2.39	86.7±3.41	13.9±0.21	35.19±0.83	10.14±0.74

Notes:

a Data are expressed as the mean ± standard deviation (n=3).

b Data are expressed as the mean ± standard deviation (n=10).

Abbreviations: CTZ, cetirizine hydrochloride; T85%, time for 85% of drug release.

Figure 2 Release profiles of CTZ from the D-LSCD formulations; (A) release profiles for F1–F6, (B) release profiles for F7–F12, and (C) release profiles for F13–F18.

Abbreviations: CTZ, cetirizine hydrochloride; D-LSCD, Draper–Lin small composite design.

Figure 3 Pareto charts of standardized effects on the particle size (A), angle of repose (B), production yield (C), encapsulation efficiency (D), loading capacity (E), initial release (F), and time for 85% of drug release (G).

Abbreviations: HLB, hydrophilic lipophilic balance; ERL, Eudragit RLPO; X₁, ERL loading percentage; X₂, emulsifier HLB; X₃, talc percentage; X₄, dispersed phase volume; X₁X₂, X₁X₃, X₁X₄, X₂X₃, X₂X₄, and X₃X₄ are the interaction terms between the factors; X₁X₁, X₂X₂, X₃X₃, and X₄X₄ are the quadratic terms between the factors.

Figure 4 Three-dimensional response surfaces with contour plots below generated from the D-LSCD demonstrating the effect of ERL loading%, emulsifier HLB, talc percentage, and the dispersed phase volume on the particle size (A), angle of repose (B), production yield (C), encapsulation efficiency (D), loading capacity (E), initial release (F), and time for 85% of drug release (G).

Abbreviations: HLB, hydrophilic lipophilic balance; ERL, Eudragit RLPO; D-LSCD, Draper–Lin small composite design; X₁, ERLloading percentage; X₂, emulsifier HLB; X₃, talc percentage; X₄, dispersed phase volume; X₁X₂, X₁X₃, X₁X₄, X₂X₃, X₂X₄, and X₃X₄ are the interaction terms between the factors; X₁X₁, X₂X₂, X₃X₃, and X₄X₄ are the quadratic terms between the factors; Y₁, particle size; Y₂, angle of repose; Y₃, production yield; Y₄, encapsulation efficiency; Y₅, loading capacity; Y₆, initial release; Y₇, time for 85% of drug release.

Figure 5 Correlations of the factors and responses.

Notes: (A) Correlation between talc% and both particle size and angle of repose, (B) correlation between Eudragit RLPO loading% and both the initial release% and the time for 85% of drug release, (C) correlation between the emulsifier HLB and both the encapsulation efficiency and the loading capacity, and (D) correlation between the dispersed phase volume and both the encapsulation efficiency and the loading capacity.
Abbreviations: HLB, hydrophilic lipophilic balance; ERL, Eudragit RLPO; EE, encapsulation efficiency; LC, loading capacity; T85%, time for 85% of drug release.

Table 3 Statistical ANOVA of the responses (Y₁–Y₇)

Factors	Particle size (Y1), µm		Angle of repose (Y2),°		Production yield (Y3), %		Encapsulation efficiency (Y4), %		Loading capacity (Y5), %		Initial release (Y6), %		T85% (Y7), h
	F-ratio	P-value	F-ratio	P-value	F-ratio	P-value	F-ratio	P-value	F-ratio	P-value	F-ratio	P-value	F-ratio	P-value
X1	1.25	0.3451	5.44	0.1020	0.44	0.5555	0.00	1.0000	0.00	1.0000	4,462.3	0.0001*	118.71	0.0017*
X2	0.02	0.9102	0.01	0.9316	0.96	0.3992	19.16	0.0221*	41.40	0.0076*	394.01	0.0003*	0.73	0.4560
X3	15.45	0.0293*	156.32	0.0011*	3.71	0.1496	1.73	0.2799	8.86	0.0588	90.39	0.0025*	0.09	0.7789
X4	10.15	0.0499*	66.60	0.0038*	24.99	0.0154*	39.63	0.0081*	35.16	0.0096*	1.04	0.3823	0.01	0.9212
X1X1	1.56	0.3006	4.43	0.1260	1.98	0.2542	0.51	0.5250	0.53	0.5197	424.50	0.0003*	5.26	0.1056
X1X2	0.17	0.7109	22.80	0.0175*	12.14	0.0399*	0.93	0.4051	9.57	0.0535	0.04	0.8535	0.02	0.8876
X1X3	0.03	0.8769	1.47	0.3121	0.28	0.6348	0.15	0.7285	0.78	0.4422	4.24	0.1315	0.90	0.4117
X1X4	0.00	0.9965	0.45	0.5499	1.76	0.2768	4.99	0.1115	11.44	0.0430*	64.96	0.0040*	0.80	0.4375
X2X2	0.54	0.5152	0.82	0.4321	5.73	0.0964	4.81	0.1159	16.65	0.0266*	95.52	0.0023*	3.57	0.1552
X2X3	0.05	0.8331	0.02	0.8976	0.60	0.4964	0.15	0.7285	0.25	0.6485	8.88	0.0586	0.18	0.6983
X2X4	0.60	0.4939	3.98	0.1400	0.03	0.8778	0.13	0.7453	0.24	0.6595	281.21	0.0005*	6.21	0.0883
X3X3	0.06	0.8188	0.66	0.4753	0.40	0.5738	0.61	0.4920	0.53	0.5197	106.07	0.0020*	3.95	0.1410
X3X4	1.86	0.2662	0.31	0.6148	0.11	0.7625	1.54	0.3025	3.58	0.1548	9.71	0.0527	0.04	0.8555
X4X4	0.10	0.7736	9.82	0.0519	3.74	0.1486	7.74	0.0688	0.21	0.6752	88.25	0.0026*	5.77	0.0956
R^2	93.201		98.849		98.324		98.213		98.843		99.982		98.687
Adj-R^2	61.471		93.476		90.505		89.875		93.442		99.898		92.557
SEE	46.174		1.516		2.885		2.875		0.560		0.208		1.052
MAE	15.753		0.515		0.982		1.147		0.201		0.062		0.405

Note:

* Significant effect of factors on individual responses.

Abbreviations: HLB, hydrophilic lipophilic balance; ERL, Eudragit RLPO; ANOVA, analysis of variance; X₁, ERL loading percentage; X₂, emulsifier HLB; X₃, talc percentage; X₄, dispersed phase volume; T85%, time for 85% of drug release; X₁X₂, X₁X₃, X₁X₄, X₂X₃, X₂X₄, and X₃X₄ are the interaction terms between the factors; X₁X₁, X₂X₂, X₃X₃, and X₄X₄ are the quadratic terms between the factors; R², R-squared; Adj-R², adjusted R²; SEE, standard error of estimate; MAE, mean absolute error.

Table 4 Optimum combination of factors, predicted values, observed values, the residuals, and the prediction error percentage for the optimized formulations of CTZ-loaded polymethacrylate microspheres

Factors	Optimum
ERL loading percentage (X1)	21.11
Emulsifier HLB (X2)	9.6
Talc percentage (X3)	6.67
Dispersed phase volume (X4)	11.09
Responses	Predicted	Observed	Residuala	Prediction errorb (%)
Particle size (Y1)	136.2	142.3	−6.1	4.48
Angle of repose (Y2)	35.29	33.25	2.04	5.78
Production yield (Y3)	83.52	84.43	−0.91	1.09
Encapsulation efficiency (Y4)	86.70	87.10	−0.4	0.46
Loading capacity (Y5)	14.32	13.79	0.53	3.70
Initial release (Y6)	30.00	28.78	1.22	4.07
T85% (Y7)	12.00	12.46	−0.46	3.83

Notes:

a Residual = predicted value – observed value.

b Prediction error (%) = (observed value – predicted value)/predicted value ×100%.

Abbreviations: HLB, hydrophilic lipophilic balance; ERL, Eudragit RLPO; CTZ, cetirizine hydrochloride; T85%, time for 85% of drug release.

Table 5 Pharmacokinetic parameters of CTZ following the administration of a single oral dose (10 mg) of the marketed tablets, and the optimized formulation of CTZ microspheres equivalent to 10 mg

Pharmacokinetic parameter	Zyrtec^® 10 mg tablet	Optimized CTZ formula
Cmax (ng/mL)	285.413±22.17	257.288±22.75
tmax (h)	1.5±0.23	6.0±0.34
AUC(0–24) (ng h/mL)	2,403.879±328.76	3,989.643±195
AUC(24–∞) (ng h/mL)	20.228±2.72	22.355±2.15
AUC(0–∞) (ng h/mL)	2,424.107±215.32	4,011.998±319.31
Kel (h^−1)	0.128±0.043	0.153±0.066
MRT (h)	8.877±1.91	11.098±0.93
Relative bioavailability (%)		165.5

Note: Data represent the mean value ± standard deviation (n=6).

Abbreviations: CTZ, cetirizine hydrochloride; C_max, maximum plasma concentration; t_max, time to reach C_max; AUC, area under the time–concentration curve; K_el, elimination rate constant; MRT, mean residence time.

Figure 6 Mean plasma concentration–time profiles for CTZ after the oral administration of a single dose (10 mg) of the marketed tablet and the optimized CTZ-loaded polymethacrylate microspheres.

Notes: Data represent the mean value ± standard deviation (n=6); *P<0.05; **P<0.001.
Abbreviation: CTZ, cetirizine hydrochloride.