1. INTRODUCTION:
Metformin is also used for women who have polycystic ovary syndrome PCOS “a worldwide health problem occurs approximately 4-18% of reproductive –aged women”[3,4]. In the United States alone, more than 48 million prescriptions were filled in 2010 for its generic formulations. Therefore, it is one of the most common prescribed drugs worldwide[5].
Because of its short biological half- life ~5 hours and low bioavailability 60%, it should be repeatedly administrated (500 mg three times a day) to maintain effective plasma concentration. The high incidence of gastrointestinal side effect (up to 25%) and the frequent dosing schedule lead to reduce patient compliance and therapeutic efficiency. Therefore, pharmaceutical companies manufactured prolonged formulations of metformin HCl which improve patient compliance, minimize side effects and enhance its absorption that is saturable and dose dependent[6,7].
In spite of these benefits of metformin prolonged release formulation, there are significant challenges due to its inherent low compressibility, high dose and high water solubility which increase the need to use suitable excipients in acceptable amounts to slow down its fast release[8].
There are many generics of metformin extended release tablets in Syria, which are generally readily available and less expensive compared to the innovator. However, generics are more likely to be spurious and substandard quality. Thus generics must exhibit equivalent pharmaceutical properties with the innovator to make them acceptable substitutes. The drug release profile of a product and drug quality as a whole could be affected by the type and the amount of the active pharmaceutical ingredient and excipients used in the manufacturing techniques process as well as the manufacturing techniques employed[9].
Drug products that are biopharmaceutically and chemically equivalent must be identical in their quality, strength, purity, and active ingredient release profile. They must to be in the same dosage form and intended for the same route of administration[10,11].
The prediction of the in-vivo bioavailability of most oral drugs depends on the in-vitro dissolution studies. Dissolution testing of drug products plays an important role as quality control tool to monitor batch to batch consistency of drug release from a dosage form[12]. It is a vital tool used to evaluate the pharmaceutical quality of generic and innovator, and to determine their possible equivalence[9].
The aim of present study is to compare metformin extended release tablets 1000 mg from two different Syrian brands A and B (two batches from each brand) with the innovator Glucophage XR®. This allow prescribers to select appropriate generic metformin tablets brands as substitutes for Glucophage XR®.
2. MATERIALS AND METHODS:
2.1. Materials:
Two commercial brands (A and B) of metformin extended release tablets were randomly selected; two batches were taken from each one plus the innovator Glucophage XR®. Metformin brand having label strength of 1000 mg. All tests were performed within product expiration dates. Sodium hydroxide and mono basic potassium phosphate were purchased from Merck-Germany. All chemicals used were of analytical grade. Freshly distilled water was used throughout the work.
2.2. METHODS:
2.2.1. Uniformity of Weight:
The USP uniformity of weight test was done by weighing 20 tablets of each product using an electronic balance (Precisa XB 220 A/ Germany), average weight was calculated. The tablets were than weighed individually and the percentage deviation from the average weight was calculated. The tablets meet the USP test if not more than two tablets are outside the percentage limits, and no one tablet differs by more than 2 times the percentage limit.
2.2.2. Assay:
Twenty tablets from each product were selected by chance, crushed and finely powdered. The powder equivalent to 1000 mg of metformin HCl was transferred into a volumetric flask which contained 700 ml of distilled water. The content was shaken well for 20 minutes for dissolving of drug completely, then sufficient quantity of water was added to produce 1000 ml. The mixture was filtered and appropriate dilution was made[13].
The absorbance of the resulting solution was taken for each product in UV-visible spectrophotometer (Spectrophotometer Jasco V-530/ vis) at 232 nm. Drug concentration was calculated from a calibration curve of standard metformin (the curve was linear between 3-12.5 µg /ml with a correlation coefficient of 0.996).
Figure 1: Standard curve of metformin HCl in distilled water
2.2.3. Uniformity of dosage units:
According to the high amount of metformin HCl 1000 mg which comprise more than 60% of each tablet weight, weight variation was applied for the test of uniformity of dosage units. Ten tablets from each product were selected randomly, weighted individually with an analytical weighting balance. The drug substance content expressed as a percentage of label claim from the weight of the individual tablet and the result of the assay, also the acceptance value (AV) were calculated for each products.
(AV) was determined by using the following formula:
AV=
M is the reference value
is the mean of the individual estimated contents expressed
as a percentage of label claim.
s is the sample standard deviation
k is the acceptability constant
k=2 when n=10, k=2.4 when n=30, where n is the sample size [14].
2.2.4 In-vitro drug release study:
In –vitro drug release study was carried out for 12 hours using USP apparatus Ι (rotated basket) (Erweka DT 600/ Germany) at 100 rpm. The dissolution medium consisted of 1000 ml of phosphate buffer pH=6.8 maintained at 37±0.5°C. 5 ml from the release medium were withdrawn at different time intervals up to 12 hours, replaced with the same amount of fresh dissolution medium to maintain the sink condition, then filtered through o.45 μ membrane filter and diluted appropriately with dissolution medium. The diluted filtrates were analyzed by UV spectrophotometer at 232 nm.
Drug concentration was calculated from the calibration curve of standard metformin HCl in phosphate buffer (concentration 3-12.5) μg /ml.
Figure 2: Standard curve of metformin hydrochloride in phosphate buffer pH= 6.8
2.2.5 Release kinetics study:
In order to study the drug release mechanism, the dissolution profile was analyzed according to the different zero-order (cumulative amount of drug released vs time), first order (cumulative percentage of remaining drug vs time) and Higuchi (cumulative percentage of drug released vs square root of time) equations. The dissolution data was also fitted according to the well-known exponential Korsmeyer-Peppas equation, which is often used to describe drug release behavior from polymeric system.
Log
(Mt/M
) = log K + n.log t
Where
Mt/M = fraction solute release
t = release time
K = kinetic constant characteristic of the drug/polymer system.
N = diffusion exponent indicating release mechanism[15,16,17].
2.2.6 Comparison of dissolution profiles:
The dissolution profiles were compared using model- independent methods: the difference factor f1, the similarity factor f2 and dissolution efficiency (DE).
The dissolution profiles are considered to be similar when f2 is between (50-100) and f1 lies below 15.
The dissolution profiles of products were compared to Glucophage XR® using f2and f1 which are calculated from the following formulas:
n= numbers of dissolution time points.
Rt, Tt individual or mean percent dissolved at each time point t for the reference and test product dissolution profiles respectively.
Dissolution efficiency (DE) was also employed to compare the drug release from various brands. DE was calculated by using range (t1-t2). DE was calculated by using the following equation:
DE = (AUC(0-t) /y100t)*100
Where
y is the percentage dissolved at time t[16,17].
2.2.7. Determination of swelling index:
The swelling index is an indication of the ability of the polymer material used to absorb water while maintaining the integrity of the tablets.
The extent of swelling was measured in terms of % weight gain by the tablet.
The swelling behavior of metformin pharmaceutical products was determined at 37°C in phosphate buffer pH=6.8 up to 12 hours. Three tablets from each product were individually weighted and kept in a petridish containing 60 ml of the buffer solution. At the end of 0.5-1-2-3-4-6-8-10-12 h the tablet was removed, blotted lightly with tissue paper to remove excess buffer.
Percentage weight gain by tablet was calculated by following formula:
Swelling index= (|w0-wt |)*100
w0
Wo is the tablet weight at time=0
Wt is the tablet weight at time=t [18,19, 20].
3. RESULT AND DISSCUSION:
3.1. Uniformity of weight:
According to the USP recommendation for tablets weighing more than 324 mg, ±5 % deviation from the mean weight is acceptable. As the results showed in table (1) the average weight deviation percentage of 20 tablets taken from each product was found to be within the above limit, and hence all the products passed the test for uniformity of weight.
Table 1: Uniformity of weight test results.
|
Maximum deviation from the average weight (%) |
Mean weight (g) |
Formulation code |
|
1.505 |
1.477 |
Glucophage XR |
|
1.925 |
1.24 |
A1 |
|
3.4 |
1.238 |
A2 |
|
2.314 |
1.607 |
B1 |
|
3.439 |
1.62 |
B2 |
3.2. Assay:
Results achieved from analysis of metformin HCl in tested products are shown in table (2). As USP specified all the batches should fall within the limit of 90-110 %. Results indicate that all products stayed on the acceptable limits.
Table 2: Amount (% of labeled) of metformin in tested and reference products.
|
B2 |
B1 |
A2 |
A1 |
Glucophage XR |
Product code |
|
101.68 |
98.07 |
101.89 |
99.9 |
100.56 |
Mean content (%) |
|
0.63 |
0.33 |
0.44 |
0.28 |
0.19 |
SD |
|
0.62 |
0.34 |
0.43 |
0.28 |
0.19 |
RSD |
3.3. Weight variation:
The requirement for dosage uniformity was met; due to the calculated acceptance values of the first ten dosage units for each product is less than 15%, as shown in table (3). Hence all the tested products exhibited uniformity of drug content.
Table 3: Mean weight, s and acceptance values for (wv) test.
|
B2 |
B1 |
A2 |
A1 |
Glucophage XR |
Product code |
|
2.17 |
1.98 |
2 |
2.98 |
0.75 |
AV |
3.4 In vitro release study:
Dissolution is the amount of substance that goes into solution per unit time under standardized conditions of liquid/ solid interface, solvent composition and temperature [21].
The results of dissolution studies indicated that Glucophage XR, A1, A2, B1 and B2 released 24.59 %, 35.83 %, 37.09%, 28.29% and 28.83% of metformin HCl at the end of 1h; and 98.84 %, 100.83%, 100.24 %, 97.31 %, 98.04 % of drug at the end of 12 hours respectively Figure (3).
The use of fit factors (f 1and f 2) was recommended for dissolution profiles comparison in the FDA´s guides for industry. According to these guides, drug release from B1 and B2 was found similar with reference brand as f 2 values were greater than 50 and f 1 values were less than 15. Whereas drug release from A1and A2 wasn’t similar with reference brand as f 2 values were smaller than 50. There was no significant difference between the batches of the brands. f 1, f 2 and DE % values which were calculated for the tested products are illustrated in Table (4).
Previous study on different metformin HCl brands in Saudi Arabia showed that five out of six brands were equivalent according to its dissolution profiles to originator[10]. Another study discussed and evaluated difference between seven brands of metformin in Nigeria market. The result revealed that the release of metformin from three brands were non equivalent to the innovator[12].
Figure 3: Dissolution profiles of metformin extended release tablets
Table 4: calculated difference, similarity factors and DE% for tested product.
|
DE% |
f 2 |
f 1 |
Formulation code |
|
67.34 |
- |
- |
Glucophage XR |
|
77.19 |
47.42 |
15.69 |
A1 |
|
78.42 |
45.24 |
17.23 |
A2 |
|
67.99 |
77.46 |
3.54 |
B1 |
|
68.72 |
80.79 |
2.84 |
B2 |