An optimized formulation of a sustained release tablet of Gliclazide was developed. The use of Doptimal design with a polynomial statistical model to analyze dissolution data reduced the number of laboratory tests required to obtain an optimal dosage form. The final formulation contained 22 mg of Methocel®E15LV, 16.5 mg Methocel®E15 and 10.0 mg of Dibasic Calcium Phosphate per 30 mg Gliclazide sustained release tablet. Dissolution studies performed on tablets from 5000 tablet test batches released greater than 90 percent of loaded drug in eight hours. Drug release from the optimized tablets followed a pattern more closely similar to zero-order than other mechanisms of drug release tested. Storage of tablets in accelerated and ambient conditions for 6 and 12 months respectively did not alter any of the physico-chemical properties, drug release or the drug release rate compared to initial observations and dissolution data of the prepared tablets. The addition of potassium phosphate and monosodium phosphate to the tablet reduced the effect pH has on Gliclazide dissolution compared to the commercially available product.
Gliclazide 1-(3-azabicyclo (3.3.0)oct-3-yl)-3-p-tolylsulphonylurea is an oral hypoglycemic agent used to treat non-insulin-dependent diabetes mellitus. Dosage forms include immediate and sustained release preparations. Gliclazide plasma half-life is approximately 12 hours [
Sustained release formulations of gliclazide have been prepared as matrix tablets, osmotic pump tablet, spheres, and pellets. Among sustained release formulations, hydrophilic matrix tablets have been studied most, probably due to the fact that matrix tablets are easily prepared due to the fact that numerous polymers, such as hydroxylpropylmethylcellulose (HPMC), hydroxypropylcellulose, sodium alginate, Eudragit® EPO, etc., can be used to prepare the hydrophilic polymer matrix system that can easily modulate the drug release kinetic process to a desired drug release rate.
Among studies on sustained release gliclazide tablets, investigators have mainly used HPMC to control drug release. In 2004, Barochez et al. [
Additional investigators have used other hydrophilic polymers besides HPMC. In 2008, Vijayalakshmi et al. [
In addition to hydrophilic matrix tablets, other dosage forms of gliclazide sustained release formulations have been studied like osmotic pump tablets and microspheres. Li et al. [
Among the aforementioned studies, several investigators used mathematical statistics and optimization me- thods in their study designs to minimize the number of trials, delineate the effect of causal factors in the formula by analyzing designed response surfaces and obtain the appropriate formulation within target goals. Response surface methodology (RSM) is a widely applied approach to design an optimized pharmaceutical formulation with an appropriate dissolution rate in a short period of time with minimum laboratory trials. Also, D-optimal design is suitable to investigate and delineate the least number of experiments to perform, analyze the effects that changes in excipient mixture composition produce and aid in the selection of the optimal excipient compo- sition for achieving the optimized formulation [
Gliclazide was a gift from Labochim® (Milan, Italy). Methocel®K15M and Methocel®E15LV were gifts from Colorcon (West Point, PA); disodium hydrogen phosphate, disodium hydrogen phosphate, methanol, and aceto- nitrile were purchased from Merck (Darmstadt, Germany). Lactose monohydrate, dibasic calcium phosphate, potassium dihydrogen phosphate, polyvinyl pyrrolidone K30 (PVP), talc, and magnesium stearate were obtained from XilongLom (Guangzhou, China). Diamicron®MR 30 mg (Lot No. 021522539, expiration date: 12/2012) was purchased from Les Laboratoires Servier (Paris, France).
Three batches of 5000 tablets of the optimal formulation were made to validate the obtained results and to evaluate the stability of the gliclazide tablets using the following processing parameters: blending time of 12 minutes at a speed of 60 rpm, and 20 minutes of wetting the mixture (150 rpm) in Sigma ERWEKA kneader (Heusenstamm, Germany), granulation through 18 mesh sieve using ERWEKA Wet Granulator (Huesenstamm, Germany), 10 minutes for mixing lubricants in ERWEKA Cube mixer (Huesenstamm, Germany) and then, as above, compressing the tablets with the same parameters in a rotary tablet machine/ZPW21A (Shanghai, China).
D-optimal design by MODDE 8.0 software along with contour surface response was used to optimize the for- mulation of gliclazide modified release tablets. The amount of Methocel®K15M (X1); Methocel®E15LV (X2) and DCP (X3) were the three independent factors. The dependent variables were the percentages of drug release after 1 hour (Y1), 2 hours (Y2), 4 hours (Y4), 6 hours (Y6), and 8 hours (Y8). The amount of lactose was adjusted to fix the weight of tablets to 161 mg while keeping the tablet’s other ingredients of gliclazide, KH2PO4, Na2HPO4·2H2O, talc, magnesium stearate and PVP constant.
Tablets hardness, 10 tablets for each test, was determined as per USP 32 using PTB-511B hardness tester, Pharma Test (Hainburg, Germany).
. Formulations, drug contents and dissolution data of gliclazide modified tablets.
Ingredients | Percent of gliclazide release (n = 3)% | ||||||||
---|---|---|---|---|---|---|---|---|---|
No | K15 | E15 | DCP | Drug Content% | |||||
(mg) | (mg) | (mg) | 1 h | 2 h | 4 h | 6 h | 8 h | ||
RP | - | - | - | 100 | 12.41 | 30.59 | 53.38 | 73.60 | 88.39 |
N1 | 10 | 10 | 10 | 105 | 20.27 | 61.96 | 90.63 | 100.00 | - |
N2 | 20 | 10 | 10 | 104.34 | 16.33 | 22.04 | 41.20 | 55.78 | 68.02 |
N3 | 10 | 30 | 10 | 99.09 | 22.34 | 48.37 | 87.13 | 100.00 | - |
N4 | 10 | 10 | 50 | 98.07 | 19.87 | 43.99 | 63.44 | 100.00 | - |
N5 | 20 | 10 | 50 | 103.09 | 11.95 | 21.77 | 40.36 | 57.89 | 70.27 |
N6 | 10 | 30 | 50 | 104.88 | 21.59 | 39.93 | 79.19 | 100.00 | - |
N7 | 20 | 30 | 50 | 99.18 | 12.40 | 21.38 | 38.32 | 55.39 | 71.09 |
N8 | 10 | 30 | 23.5 | 100.94 | 22.62 | 46.39 | 80.44 | 100.00 | - |
N9 | 10 | 30 | 36.5 | 97.20 | 26.64 | 53.44 | 91.39 | 100.00 | - |
N10 | 10 | 16.5 | 10 | 96.13 | 24.12 | 81.19 | 100.00 | - | - |
N11 | 10 | 23.5 | 10 | 102.79 | 17.45 | 41.32 | 84.80 | 100.00 | - |
N12 | 13.5 | 30 | 10 | 104.96 | 13.50 | 31.24 | 55.03 | 77.23 | 87.77 |
N13 | 20 | 20 | 30 | 103.42 | 11.34 | 29.27 | 49.02 | 66.64 | 81.17 |
N14 | 15 | 10 | 30 | 101.04 | 22.12 | 30.24 | 58.34 | 79.21 | 96.06 |
N15 | 15 | 20 | 50 | 104.98 | 18.98 | 37.66 | 63.80 | 81.63 | 99.02 |
N16 | 15 | 20 | 30 | 103.02 | 16.28 | 33.10 | 61.02 | 80.11 | 98.85 |
N17 | 15 | 20 | 30 | 102.20 | 17.58 | 43.79 | 73.18 | 98.86 | 100.00 |
N18 | 15 | 20 | 30 | 100.76 | 14.23 | 32.22 | 65.07 | 86.25 | 98.12 |
N19 | 15 | 20 | 30 | 97.24 | 18.68 | 37.85 | 65.13 | 84.02 | 95.19 |
RP is the reference product (Diamicron®MR 30 mg).
UV-Vis method (used for freshly prepared formulations): Assay of drug content was performed in triplicate for each gliclazide tablet formulation. An amount of powder equivalent to 26 mg of gliclazide was weighed and transferred to a 50 ml volumetric flask. Methanol (20 ml) and pH 6.8 phosphate buffer solution (30 ml) were used to dissolve the drug under sonication for 15 minutes. Then samples were filtered through a 0.45 µm di- ameter membrane. Filtered solutions were diluted 50 times with a pH 6.8 phosphate buffer solution and the drug content of the diluted solutions were measured using a UV spectrometer (UV spectrometer model Hitachi U- 1900, Tokyo, Japan) set at a wavelength of 226 nm. The quantity of gliclazide present was determined using a standard curve from drug solutions prepared in pH 6.8 phosphate buffer.
HPLC method: Sample solutions and standard solutions were prepared in the same manner as that of UV-Vis method. The final samples were filtered through a 0.45 µm diameter membrane before injection into HPLC sys- tem (Shimadzu, Kyoto, Japan) with the following chromatographic conditions: Mobile phase: acetonitrile: phos- phate buffer 0.01 N (60:40) (adjusted to pH 3.0 with phosphoric acid), Phenomenex C8 column (250 × 4.6 mm, 5 µm), mobile phase flow rate of 1.0 ml/minute at 30˚C ± 1˚C, the injection volume of 2.0 µl, with 6 µg glipi- zide as internal standard, and the UV detector set at a wavelength of λ = 226 nm.
Dissolution studies to determine drug release from each of three or six tablets were performed according to the USP 32, apparatus 2, using 900 ml 0.1 N hydrochloric acid solution for dissolution the first hour and in 900 ml phosphate buffer solution of pH 6.8 over the next 7 hours with a 75 rpm stirring speed. 10 ml samples were col- lected at predetermined time intervals for the eight hour dissolution study. After collection, the samples were filtered through a 0.45 µm diameter membrane. Filtered drug solution concentrations measured by UV absor- bance at 226 nm were compared to gliclazide standard solutions in pH 6.8 phosphate buffer. Once the gliclazide dissolution samples’ concentrations were measured via UV the results were converted to percentage of glicla- zide released. Gliclazide dissolution profiles are presented as percent drug release versus time curves.
Comparison of two drug dissolution release profiles (reference versus test formulations) was performed using the similarity factor, f2, which is calculated as follows (Equation (1)) [
where Rt and Tt are the percentages of drug release at time t for the reference and the test formulation, respec- tively; n is the number of time points. If f2 is equal to or more than 50, the two drug release profiles will be con- sidered to be similar.
Dissolution data from gliclazide sustained release tablets were fitted to various mathematical models such as zero-order, Higuchi, First-order, Weibull, Hixson Crowell, Korsmeyer Peppas and Hopfenberg equations. Val- ues for the AIC (Akaike criteria) were used as basis for comparison (Equation (2)) [
where, n is the sample size, σ is the residual standard error which was calculated using S-plus 8.0 statistical software (TIBCO Software Inc., Palo Alto, CA, 94304), and p is the number of parameters in the model.
Stability studies were carried out with tablets from the optimal formulation batches of 5000 tablets. The modi- fied release tablets were placed in dark bottles following ICH guidelines at accelerated conditions (40˚C ± 2˚C, RH 75%) in a cooling incubator, Climacell (MMM Medcenter GmbH, Gräfeling, Germany) for six months and ambient room temperature for twelve months. The physicochemical and aesthetic properties of the tablets were evaluated including parameters such as appearance, moisture, hardness, drug content, and in vitro drug release profiles.
Convolution was performed using Kinetica 5.0 (Innaphase, Philadelphia, PA) to simulate plasma concentration time curves of gliclazide after oral administration of Diamicron®MR and the optimal test formulation. Convolu- tion was performed with the following assumptions. The first is that the absorption phase is considered to be that the drug is given as series of IV bolus injections. The second is that gliclazide’s bioavailability is 0.97 and that gliclazide elimination from the body can be described by IV administration data based on the study by Delrat et al., 2002 [
A preliminary study was carried out to select the range of input variables that influence the response variables (not shown).
The regression equations of each term were described by the following:
where X1, X2 and X3 were amounts of Methocel®K15M, Methocel®E15LV and DCP, respectively; bi was statistically significant when p-value ˂ 0.05; Yi is the percentage of Gliclazide release at time = i hour.
The regression coefficients for each term in the full regression model are summarized in
.The regression coefficients (bi) for each term in the full regression model.
bi | Y1 | Y2 | Y4 | Y6 | Y8 | |||||
---|---|---|---|---|---|---|---|---|---|---|
Value | p | Value | p | Value | p | Value | p | Value | p | |
b0 | 18.40 | ˂0.001 | 41.48 | ˂0.001 | 71.86 | ˂0.001 | 93.36 | ˂0.001 | 101.79 | ˂0.001 |
b1 | −4.13 | 0.002 | −14.03 | 0.002 | −19.41 | ˂0.001 | −15.64 | ˂0.001 | −9.22 | ˂0.001 |
b2 | −0.69 | 0.397 | −3.65 | 0.176 | −2.39 | 0.136 | −1.94 | 0.311 | −1.29 | 0.166 |
b3 | 0.64 | 0.435 | −0.58 | 0.822 | −1.16 | 0.449 | 0.57 | 0.761 | 1.02 | 0.264 |
b4 | 0.16 | 0.899 | 1.98 | 0.612 | 1.91 | 0.411 | −2.04 | 0.476 | −3.16 | 0.037 |
b5 | 0.19 | 0.868 | −3.97 | 0.289 | −4.82 | 0.044 | −2.80 | 0.302 | −3.29 | 0.023 |
b6 | −0.69 | 0.546 | −0.88 | 0.806 | −3.37 | 0.134 | −3.04 | 0.261 | −2.93 | 0.037 |
b7 | −1.05 | 0.211 | 0.03 | 0.990 | −2.92 | 0.076 | −1.27 | 0.501 | 0.22 | 0.804 |
b8 | −0.09 | 0.907 | 3.84 | 0.157 | 4.22 | 0.018 | 0.71 | 0.703 | −0.12 | 0.891 |
b9 | 0.96 | 0.212 | 3.77 | 0.133 | 4.17 | 0.012 | 2.69 | 0.139 | 0.94 | 0.261 |
. Summary of statistical results from the final regression model and full model.
Parameter | Y1 (1 h) | Y2 (2 h) | Y4 (4 h) | Y6 (6 h) | Y8 (8 h) |
---|---|---|---|---|---|
R2 | 0.766 | 0.780 | 0.954 | 0.912 | 0.959 |
R2 adjusted | 0.532 | 0.579 | 0.908 | 0.824 | 0.917 |
Q2 | 0.265 | 0.194 | 0.455 | 0.454 | 0.499 |
p-value | 0.046 | 0.031 | 0.000 | 0.001 | 0.000 |
p-value lack of fit | 0.186 | 0.128 | 0.446 | 0.730 | 0.176 |
In addition, response surface analysis also shows the influence of the input variables on the output variables.
Based on the data from the experimental results and dissolution data of Diamicron®MR 30 mg tablets, the range of optimal conditions are presented for dependent variables (Y1, Y2, Y4, Y6 and Y8) in
Three batches of 1000 tablets of the optimal formulation were prepared to confirm the predictability of the model. The dissolution profiles of the three batches of optimal formulation tablets were the same as that of Dia- micron®MR 30 mg (f2 equal to 67.71, 80.09 and 80.39 for batch 1, 2, and 3, respectively).
Triple batches of 5000 tablets of optimal formulation were also prepared by the same wet granulation method, but using laboratory kneader, wet granulator, cube mixer and rotary tablet press (presented in Materials and Methods). Several properties of the granule (including Carr’s index, and moisture) and tablets (hardness, drug content and dissolution) were evaluated and shown in
. The assayed contents of drug from all batches were between 95% and 105%. The tablets’ hardness was within the range of 45 - 75 N and the weight variation of tablets complied with the general requirements for tablets. Thus, replication of three batches was shown at the scale of 5000 tablets using laboratory equipment
(a)
Response surface plots of input variables (X1, X2, and X3) versus the percentage of Gliclazide released at 4 hours (Y4)
. Optimal ranges of dependent variables.
Dependent Factors | Range |
---|---|
Y1 = percent release in 1 hr | 10% ≤ Y1 ≤ 15% |
Y2 = percent release in 2 hr | 28% ≤ Y2 ≤ 33% |
Y4 = percent release in 4 hr | 50% ≤ Y4 ≤ 56% |
Y6 = percent release in 6 hr | 70% ≤ Y6 ≤ 76% |
Y8 = percent release in 8 hr | 85% ≤ Y8 ≤ 91% |
. The optimal formulation of Gliclazide modified release tablets.
Ingredients | Weight/Tablet (mg) |
---|---|
Gliclazide | 30.0 |
Lactose | 65.0 |
KH2PO4 | 2.5 |
Na2HPO4∙2H2O | 5.0 |
PVP K30 | 8.0 |
Methocel®K15M | 16.5 |
Methocel®E15LV | 22.0 |
DCP | 10.0 |
Talcum | 1.2 |
Magnesium Stearate | 0.8 |
. Physico-chemical properties of granules and tablets for three batches of optimal formulation.
Batch | Granule characteristic | Tablet characteristic | |||
---|---|---|---|---|---|
Carr’s index | Moisture | Hardness | Drug Content | Weight variation | |
n = 3 | (%) n = 3 | (N) n = 10 | (%) n = 3 | (mg) n = 20 | |
B1 | 12.70 | 2.51 | 60.69 ± 6.78 | 100.37 ± 2.01 | 161.79 ± 1.46 |
B2 | 12.50 | 2.37 | 62.29 ± 8.01 | 99.48 ± 1.92 | 162.07 ± 0.98 |
B3 | 12.70 | 2.66 | 56.77 ± 9.38 | 100.43 ± 1.31 | 161.63 ± 0.45 |
The dissolution profiles of tablets from three final batches of 5000 tablets are equivalent to dissolution profile of Diamicron®MR 30 mg tablets as shown in
Gliclazide dissolution profiles of three optimal formulation batches, 5000 tablets (n = 6): B1 = Batch 1; B2 = Batch 2; B3 = Batch 3
Dissolution profilesof Diamicron®MR 30 mg and optimal formulation (OF) in different pH solutions. Where
similar (f2 is 61.4). However, the dissolution profile of the optimized formulation tablets at pH 4.5 differs from that of optimized formulation tablets at pH 1.2 and 6.8.
Results of fitting of dissolution data to mathematical models are presented in
Using convolution calculations and assuming a linear relationship between dissolution and absorption for both Diamicron®MR and optimal formulation tablets, simulation was performed to predict the drug concentrations versus time curves for these two products in a bioavailability study.
Dissolution and drug contents results from the stability study in accelerated and ambient conditions are summa- rized in
Gliclazide is a hydrophobic weak acid, insoluble in water and acidic pH, but soluble in solutions having a pH near or rising towards neutral to alkaline pH. Variation in pH results in inconsistent and irregular release of drug from the commercial dosage form, which is not a desirable feature [
. The summary of residual standard errors and AIC for the gliclazide dissolution profile of the optimal formulation- fitted by regression to the drug release models.
Release Process Tested | Equation | σ | k | n | AIC |
---|---|---|---|---|---|
First-order | C = 100 × (1 − e−kt) | 6.570 | 0.198 | - | 611.921 |
Weibull | . The summary of residual standard errors and AIC for the gliclazide dissolution profile of the optimal formulation- fitted by regression to the drug release models. | 5.372 | 0.131 | 1.269 | 548.698 |
Hixson | C = 100 × (1 − (1 − kt)3) | 5.341 | 0.056 | - | 544.813 |
Korsmeyer-Peppas | C = ktn | 4.742 | 15.904 | 0.832 | 508.268 |
Hopfenberg | C = 100 × (1 − (1 − kt)n) | 4.778 | 0.093 | 1.540 | 510.731 |
Zero-order | C = Co + kot | 5.082 | 10.750 | - | 530.728 |
Higuchi | C + Co + kHt1/2 | 8.964 | 29.128 | - | 714.602 |
C and Co is the percentage of drug released at time t and t = 0, respectively; k is the rate constant; σ is residual standard error of each model.
Simulated plasma concentration versus time curves of optimized formulation and Diamicron®MR: o = Optimized formulation; Δ = Diamicron®MR
Dissolution profile of OF tablets from batch 1 under different storage conditions. Note:
and potassium dihydrogen phosphate to obtain an alkaline microenvironment around tablet to minimize the var- iation of drug release that is characteristic of gliclazide sustained release tablets in different pH dissolution me- dia. However, the results of the dissolution profiles in different pH dissolution media while not exactly identi- cal showed minimal differences in dissolution profiles at pH 1.2 and 6.8 that are acceptable based on f2-value (61.3).
. Contents and dissolution of gliclazide from optimal formulation in different storage conditions.
Time (months) | Sample | Drug content (%), n = 3 | % Drug Release, n = 6 | f2 | |||||
---|---|---|---|---|---|---|---|---|---|
Y1 | Y2 | Y4 | Y6 | Y8 | |||||
T = 0 | B2 | 99.48 ± 1.92 | 13.36 | 33.19 | 50.24 | 72.36 | 90.96 | 75.49 | |
B3 | 100.43 ± 1.31 | 14.15 | 35.03 | 51.83 | 76.38 | 90.45 | 74.53 | ||
t = 3 | B2 | a | 104.56 ± 1.39 | 15.81 | 36.77 | 54.17 | 74.71 | 92.04 | 71.48 |
b | 102.43 ± 3.12 | 16.41 | 39.39 | 61.72 | 83.67 | 98.55 | 52.82 | ||
B3 | a | 104.87 ± 1.62 | 18.79 | 36.96 | 53.56 | 76.30 | 89.43 | 69.97 | |
b | 102.52 ± 1.35 | 14.07 | 31.11 | 51.98 | 74.21 | 93.08 | 80.64 | ||
t = 6 | B2 | a | 104.04 ± 0.72 | 10.05 | 25.41 | 47.90 | 69.17 | 88.01 | 69.03 |
b | 101.58 ± 0.81 | 12.00 | 28.13 | 49.57 | 70.53 | 90.30 | 76.28 | ||
B3 | a | 104.58 ± 1.67 | 13.22 | 29.41 | 51.60 | 71.04 | 91.26 | 79.64 | |
b | 104.41 ± 1.25 | 11.82 | 31.02 | 54.04 | 74.78 | 91.33 | 86.29 | ||
t = 12 | B2 (a) | 102.44 ± 1.98 | 14.69 | 30.67 | 53.97 | 78.44 | 97.69 | 76.43 | |
B3 (a) | 101.06 ± 2.22 | 14.00 | 34.45 | 55.73 | 75.61 | 92.95 | 73.75 |
Note: a = ambient condition, b = accelerated condition; B2 = Batch 2, 5000 tablet, B3 = Batch 32, 5000 tablets,
Zero-order release of gliclazide from sustained release tablets was shown for the entire 8 hours of the dissolu- tion test. The results agree with the results of Jin et al. (HPMC K15M, and sodium alginate, 2008) [
Utilizing MODDE 8.0 software to execute D-optimal mixture design with a polynomial statistical model in the study reduced the number of experiments and the contour surface response diagrams for multiple response optimization allowed rapid optimization of the formulation for the gliclazide modified release tablets. The prep- aration process for gliclazide modified release tablets was reproducible in the laboratory setting. Gliclazide sus- tained release tablets were stable for 6 months in accelerated storage conditions. The dissolution profiles re- mained unchanged throughout for both storage conditions. In particular, the dissolution profiles of gliclazide sustained release tablets were considered equivalent to that of Diamicron®MR 30 mg tablets in vitro.
An optimized formulation of a sustained release tablet of Gliclazide was developed. The use of D-optimal de- sign to analyze dissolution data with a polynomial quadratic statistical model reduced the number of laboratory tests required to obtain an optimal dosage form and worked to provide results that rival surface response ap- proaches in predicting an optimal formulation. The final optimized formulation (OF) of the sustained release 30 mg Gliclazide tablet contained 22 mg of Methocel®E15LV, 16.5 mg Methocel®K15M and 10.0 mg of Dibasic Calcium Phosphate. Dissolution studies performed on tablets from 5000 tablet test batches released greater than 90 percent of loaded drug in eight hours. The formulation is readily reproducible as three 5000 tablets batches showed no differences in drug release during dissolution drug testing. Drug release from the optimized tablets followed a pattern similar to zero-order more closely than other mechanisms rested. Storage of tablets in accele- rated ambient conditions for 6 and 12 months respectively did not alter any of the physico-chemical properties of the tablet; drug release or the drug release rate compared to initial dissolution or measured data of the pre- pared tablets. The addition of potassium phosphate and monosodium phosphate dihydrate to the tablet reduced the effect pH has on Gliclazide dissolution compared to the commercially available Diamicron®MR product.
The authors declare no conflict of interest. Deep appreciation is given to the National Institute of Pharmaceutical Technology, Hanoi University of Pharmacy, Hanoi, Vietnam for their support to conduct this research.