In vitro evaluation of sustained released matrix tablet formulations of clarithromvcin

Sustained release matrix tablets of clarithromycin were prepared using different polymers as Hydroxypropyl methylcellulose (H PMC), Carbopol 934 and Eudragit RLIPO by direct compression technique. For the quality control of these formulations, weight deviation, hardness, friability, diameter-height ratio, content uniformity of the active substance and in vitro dissolution technique were performed. HPLC was used for the assay of clarithromycin and the assay method was validated. Dissolution profiles of the tablets were plotted and evaluated kinetically. The effects on drug release of polymer type and concentrations were investigated by z3 factorial design. The tablets containing HPMC, Carbopol 934 and Eudragit RLIPO were found suitably to sustain drug release.


Introduction
When designing an oral sustained release formulation, the hydrophilic matrices present an alternative to other monolithic or multi particulate pharmaceutical dosage forms.Hydrophilic matrices became extremely popular in controlling the release of drugs [I, 2, 31.Acrylic acid and cellulose derivatives may be used for hydrophilic matrices for controlled release oral delivery [4,5,6,7,8,91 phosphate, in the gel layer of initially glassy HPMC matrices were studied by Colombo et al [lo].It was demonstrated that drug release kinetics does not only depend on drug diffusion and matrix erosion, but also on drug dissolution in the gel and on polymer relaxation.Celebi and ~n l u [ I l l evaluated hydrophilic matrix tablets of diltiazem using three grades of HPMC according to 23 factoriel design.They reported the effect of the polymer ratio on diltiazem release from matrix tablets.P6rez-Marcos et a1 [ I 21   clarithromycin in different laboratories, as in a collaborative study.An important step in the validation of any analytical method is the establishment of the relationship between released % (y) and the concentration of the analyte (x) and the method may be calibrated.When correlation coefficient is above 0.9990, the assay method was acceptable.The satisfying recoveries confirm the suitability of the proposed method for the routine analysis of clarithromycin in pharmaceuticals (Table 4) [23, 25,26].According to the results, the proposed method is able to access the analyte in the presence of common excipients and hence, it can be considered specific.Results in Table 5 indicate that clarithromycin showed good detection limit.

Tab. 3. Repeatability and precision of HPLC (clarithromycin peak response) (RSD %)
The effects of polymer type and concentration on in vitro release of clarithromycin has also been investigated.Drug release profiles are given in

The combination of diffusion and erosion release mechanisms in matrix
systems comprising an insoluble hydrophobic and a hydrophilic gel-forming part depends greatly on the wettability of the added drug.Furthermore, with wettable and water soluble drugs, the matrices swelled and releases were mainly achieved by diffusion and erosion due to dissolution of the gel formed.However, with less wettable drugs, the matrix erodes, due to deaggregation caused by the inability of the matrix to accommodate the swelling of gel forming hydrophilic part.
All chemicals were of analytical grade.

Factorial Design
The effect of HPMC (A), Carbopol 934 (B) and Eudragit RLIPO (C) was studied in separate 23 factorial experiments.The levels and variation intervals for the eight treatment combination are the calculation matrix for a Z3 factorial design, with the following combinations of factors A, B and C at two levels (3.33-10 %): (I), a, b, ab, c, ac, bc, and abc.We used 3 factors, each at only two levels in Table 6.These levels are polymer concentrations, the "high" and "low" levels of a factors, or presence and absence of a factors [21,22].types of methods are Accuracy, Precision, Specificity, Detection limit, Quantitation limit, Linearity and Range [20,23,24, 251.

Tab. 6. Factorial design parameters and experimental conditions
Precision: The precision of an analytical method is the degree of agreement among individual test results when the method is applied repeatedly to multiple sampling of a homogenous sample.0.0498, 0.498 and 4.98 pglmL solutions were prepared using stock solution of clarithromycin.The peak responses of these samples were measured.The standard deviation or relative standard deviation (coefficient of variation) of a series of measurements were calculated.
Same procedure was made on different days.
Accuracy: The accuracy of an analytical method is the closeness of the test results obtained by that method to the true value.0.0498-4.98pg1mL solutions were prepared using stock solution of clarithromycin.The peak responses of these samples were measured.Regression equation and regression coefficients were then calculated.Accuracy is calculated as the percentage of recovery by the assay of the known added amount of analyte (three concentrations: 0.0498, 0.498, 4.98 pg/mL) in the sample using regression equation (n=6).
Specificity: The specificity of an analytical method is its ability to measure accurately and specifically the analyte in the presence of components that may be expected to be present in the sample matrix.Specificity may often be expressed as the degree of bias of test results obtained by analysis of samples containing added impurities, degradation products, related chemical compounds, or placebo ingredients when compared to test results from samples without added substances.This bias may be expressed as the difference in assay results between the two groups of samples.
Detection and quantitation limits: The limits of detection is a parameter of limit tests.It is the lowest concentration of analyte in a sample that can be detected.
Limit of quantitation is a parameter of quantitative assays for the low levels of compounds in sample matrices, such as impurities in bulk drug substances and degradation products in finished pharmaceuticals.

In vitro dissolution studies and evaluation of release kinetics
Dissolution tests were performed according to the paddle method described in USP 26, Apparatus II.The rotating speed was 50 rpm and the temperature was 37k0.50C.Dissolution studies were carried out in 900 mL 0.1 M Sodium acetate buffer. 1 mL of samples were taken from the dissolution media at appropriate time intervals with the aid of an injector fitted with a Schleicher-Schuell filter paper having a porosity of 0.5 vm or finer, and use the filtrate as the assay preparation.The peak responses of the samples were recorded.The amounts of clarithromycin released were evaluated by using the standard calibration curve equation (n =6).
The results thus obtained were evaluated kinetically by zero, firstorder, Hixson Crowell, RRSBW, Q Square Root of Time, Higuchi equation, Spherical, Cylindrical and Slab Erosion (the rate constant k', k" and k"' were obtained according to Hopfenberg).The release rate constants (k), correlation coefficients (r) and determination coefficients (r2) were calculated by means of a computer program [30].
The in vitro release profiles (percentage of drug released versus time) obtained from the clarithromycin matrix tablet formulations were fitted to the main models which have been proposed to describe drug release kinetics from tablets and other polymer matrices.
. The drug volume fraction profiles of a colored and very soluble drug, buflomedil pyridoxal et al.: evaluated the possible use of three types of Carbomer, with different molecular weights, in the formulation of hydrophilic furosemide matrices.Their results showed that variables associated with the type and proportion of carbomer, with insignificant effects on porosity, play an important role in the release characteristics of the active principle.The acrylic polymers Eudragit RL, RS and NE were developed for pH-independent, delayed release of active ingredients by diffusion from oral dosage forms (swellable, permeable coating and matrix structures) [13].Metha et al [I41 investigated release performance of a poorly soluble drug from a novel, Eudragit-based multi-unit erosion matrix.Matrix erosion and drug release followed zero order kinetics.Clarithromycin is a semi-synthetic macrolide antibiotic.It is used in the treatment of leprosy, upper tunistic mycobacterial infections, respiratory-tract, skin and soft-tissue infections.It is given 250 mg twice daily by mouth, increased to 500 mg twice daily if required [I 5,16,17].Hig h-performance liquid chromatography (HPLC) is routinely used for the selective and accurate determination of clarithromycin in pharmaceutical matrices [ I 8, 19, 201.The aim of the work was to evaluate the influence of polymer type and concentration on dissolution rate of matrix tablets.Matrix tablets of clarithromycin were prepared by direct compression technique.The objective of this work is to outline 23 factorial design and to study the effect of three factors; HPMC, Carbopol 934 and Eudragit RLIPO on the dissolution rate of clarithromycin in matrix tablets [ I 1,211.The ideal matrix tablet formulation was found by evaluating of these findings and evaluated kinetically.For the quality control of tablets, physical control and in vitro dissolution techniques were performed.HPLC was used for the assay of clarithromycin and the assay method was validated.Dissolution profiles of each tablet were plotted.Results and Discussion Application of factorial design experiments to pharmaceutical problems has appeared to be extremely useful.The effects of several factors (A, B and C ) and their interactions (ab, bc, ac and abc) can be determined simultaneously by factorial design experiments [ I 1,21,22].Calculation of total effects for Z3 factorial design and the effects of A, B and C and their interactions on the T values are shown in

Figure 1 and 2 ( 4 .Parameters
Figure 1 and 2 (n=6).The drug release from matrix tablets depended upon the concentration and type of polymers.Approximately 85 % clarithromycin was released in the first five hours from F1 (without polymer).The release of clarithromycin from matrix tablets was different than that of control tablets (FI).

ISquare root of timeFig. 3 .
Fig. 3.The release of clarithromycin from F6 and F8 according to Higuchi equation.

FactorsTab. 7 .Contents
Eight formulations were prepared on an instrumented single-punch tablet machine by direct compression technique.Magnesium stearate was used as the lubricant (1.0 %) and HPMC, Carbopol 934 and Eudragit RLIPO were the polymers in different concentrations(3.33-10%).Contents of matrix tablet formulations are given in Table7.Each formulation was prepared separately.All ingredients of each formulation were mixed in cubic mixer.The position of the bottom punch face in the bore determines the volume of the die-cavity and hence the tablet weight.Tablet hardness was adjusted using hardness control nut.The following tests were applied to the tablets; amount of clarithromycin, crushing strength, diameter-height ratio and friability.Tablet weight uniformity to USP 26 and tablet thickness was determined using a micrometer.Tablet hardness tests were carried out using a Monsanto hardness tester.For friability tests, twenty tablets were weighed (W1) and rotated at one hundred revolutions for 4 min in a Roche friabilator.The tablets were then reweighed (W2) and the percentage friability (%F) was calculated.Content of matrix tablet formulations of clarithromycinTablet Code NoAssay method and its validationHPLC method with a 210 nm DAD detector, 250~4.6 mm Ultracarb C20 column was used for clarithromycin assay[ I 8, 19, 201.Flow rate is about 1.0 mL per minute and injection volume is 20 pL.Methanol and 0.067 M monobasic potassium phosphate (650:350) were used as mobile phase (adjusted with phosphoric acid to a pH of 4).49.8 mg clarithromycin was weighed accurately and dissolved in 10 mL mobile phase (4.98 pglmL stock solution).Six samples of 0.1-5.0mL were taken from this stock solution and diluted to 10 mL with mobile phase (0.0498-4.98 pgImL solutions).Clarithromycin peak responses of these samples were determined.Regression equation and regression coefficients were calculated to be y=ll39.67x-5.73 and r = 0.9999.Validation of an analytical method is the process by which it is established, by laboratory studies, that the performance characteristics of the method meet the requirements for the intended analytical applications.The validation of the