Formulation and evaluation of simvastatin buccal film

Article history: Received on: 12/11/2014 Revised on: 11/12/2014 Accepted on: 19/01/2015 Available online: 27/04/2015 The aim of this work was to develop and evaluate a buccal film for delivery of simvastatin. Buccal films containing carboxymethyl cellulose (CMC) with and without Polyvinylpyrrolidone (PVP) as polymers were prepared. Tween 80 was included with and without propylene glycol (PG) to modulate the characteristics of the films. The films were prepared by solvent casting with drug concentration being maintained at 2.5 mg/cm. In absence of Tween and PG, the films were opaque due to precipitation of drug. PG reduced the swelling index and increased the thickness of the film due to shrinkage. Incorporation of PVP into the films increased the bioadhesion force and time. The rate of drug release depended on the composition of the film with the presence of PVP increasing the release efficiency compared to the corresponding PVP free films. Similarly, incorporation of PG increased the drug release efficiency. Thermal analysis indicated the presence of the drug in amorphous form or as a solid solution in the film components. The developed films are promising for buccal administration of simvastatin.


INTRODUCTION
Simvastatin belongs to the statins which is lipid lowering group.They act by inhibiting the 3-hydroxy3methylglutryl coenzyme A (Schachter, 2004).In the past few years, several novel indications for statin therapy was emerged (Paraskevas et al., 2008).It was shown to reduce vascular inflammation, attenuate myocardial injury (Tandon et al., 2005), decrease the incidence of Alzheimer's disease and dementia (Fassbender et al., 2001), limit the progression of inflammatory diseases (Christensen et al., 2006), and treat chronic periodontitis (Pradeep and Thorat, 2012).Simvastatin is water insoluble crystalline powder (Ungaro et al., 2010).It undergoes extensive first pass metabolism in the liver which results in very low and variable oral bioavailability.The properties of drug like short half-life (2-3 hour), small dose size (5-80mg) and low molecular weight (418.57)makes it suitable candidate for administration by buccal route (Hiremath, 2009).This route of administration is expected to overcome the problem of poor oral bioavailability by at least avoiding the presystemic metabolism of the drug.
. In addition, buccal delivery can be useful in treatment of chronic periodontitis.Moreover, buccal drug absorption can be promptly terminated in case of toxicity by removing the dosage form the buccal cavity.It is also possible to administer drugs to patients who cannot be dosed orally (Vishnu et al., 2007).The recent years saw the introduction of a number of mucoadhesive dosage forms for buccal drug delivery.These include buccal tablets, discs, films, and semisolid products such as gels.Of these systems, buccal films are preferable over tablets and discs in terms of patient comfort and flexibility with high potential for accurate drug dosing and longer residence time compered to semisolid formulations (Verma et al., 2011).Accordingly, the objective of this work was to develop and evaluate a buccal film for delivery of simvastatin.

Preparation of simvastatin buccal films
Table 1 presents the composition of different buccal films.The buccal films were prepared by solvent casting method (Mahajan et al., 2011) in which the polymers were dissolved in water to form a clear solution.The drug was dissolved in ethanol before mixing with the polymer solution.Tween 80 and/or propylene glycol were added to the mixture.The solution was casted into a petri dish (78.6 cm 2 ) and dried.The dry film was cut into square shaped sections (4 cm 2 ).

Weight uniformity
The individual weight of 3 samples (4 cm 2 ) of each formulation was determined using an electrical balance (Semalty et al., 2008).The results were analyzed for mean and standard deviation.

Thickness uniformity
The thickness of 3 samples (4 cm 2 ) of each formulation was determined using the Vernier Caliber (Giradkar et al., 2010).The results were analyzed for mean and standard deviation.

Folding endurance
Folding endurance was determined by repeatedly folding the film at the same place till it broke or folded up to 200 times without breaking (Khairnar et al., 2009).

Drug content uniformity
The medicated film (4 cm 2 ) which is expected to contain 10mg of simvastatin theoretically was dissolved in 50 ml ethanol.The solution was suitably diluted with ethanol before determination of the drug concentration spectrophotometrically at a λ max of 238 nm (Hiremath, 2009) using UV spectrophotometer (Thermo Fisher Scientific, Madison, USA).The experiment was performed in triplicate and the drug content was expressed as percentage of the labeled using the following equation: Drug content (%) = (Experimental drug content / Theoretical drug content) x 100

Microenvironment pH
The microenvironment pH of the prepared buccal films was determined to ensure palatability of the film.A combined glass electrode was used for this purpose.The films (4 cm 2 ) were soaked in 5ml of distilled water for 1hr at ambient temperature.The surface pH was recorded by mounting the electrode on the surface of the swollen film and allowing it to equilibrate for 1 minute (Khairnar et al., 2009).The experiment was performed in triplicate.

Swelling index
The film sample (1 cm 2 ) was placed in a pre-weighed stainless steel basket of the dissolution apparatus.The loaded basket was weighed before being submerged into 200ml phosphate buffered saline (PBS, pH 7.4).The loaded basket was taken out of the bath and reweighed after carful removal of any surface moisture by gentle wiping with tissue paper.The increase in the weight of the film was determined at each interval (5, 10, 15, and 30) and the experiment was continued until a constant weight was observed.The swelling index was calculated using the formula (Koland et al., 2010): Swelling index = (W t -W 0 )/W 0 Where W t is the weight of the film at time t and W 0 is the weight of the film at zero time (before coming into contact with PBS).

In vitro bioadhesion strength
The bioadhesive strength of the prepared simvastatin films was measured using rabbit intestine as a model mucosal membrane (Nafee et al., 2003).The animals were sacrificed immediately before the start of the experiment.The rabbit intestine was excised and washed gently with phosphate buffer pH 6.6.The intestine was cut longitudinally to expose the mucosal surface.This was cut into rectangular pieces (4cm 2 ).These were glued with cyanoacrylate adhesive on the ground surface of a holder made of cellulose acetate plastic film so that the mucosal surface is uppermost.The buccal film (4cm 2 ) was glued to another holder of the same size.The surface of the rabbit intestine was moistened with phosphate buffer pH 6.6.The two holders with rabbit intestine and buccal film were put in contact with each other with uniform and constant light pressure between fingers for one minute (preload time) to facilitate adhesion bonding.The upper tissue holder was allowed to hang on an iron stand with the help of an aluminum wire fastened with a hook fixed on the back of the holder.A pre-weighed light weight polypropylene bag was attached to the hook on the backside of the lower film holder with aluminum wire.After a pre-load time of one minute, water was added to the polypropylene bag using a burette adjusted to deliver water at a rate of 2.0 drops per second until the film was detached from the tissue.The collected water in the bag was measured and expressed as the weight (gram) required for the detachment (bioadhesive strength) (Alanazi et al., 2007).The force of adhesion and bond strength was calculated according to the following equations (Habib et al., 2010): Force of adhesion (N) = (Bioadhesive strength (g) x 9.81)/1000 Bond strength (N m -2 ) = Force of adhesion / film surface area

In vitro bioadhesion time
The in vitro residence time of simvastatin films was evaluated by assessing the time required for these films to detach from rabbit intestinal muocsa (Singh et al., 2008).The rabbit intestinal mucosa was fixed with mucosal side facing up on the surface of a glass slide cover slips using cyanoacrylate glue.The mucosa was moistened with phosphate buffer solution (pH 6.6).The film (1 cm 2 ) was wetted with the same buffer and was pasted to the rabbit intestinal mucosa by applying a light force with fingertip for one minute.The whole assembly was placed in the dissolution vessel so that the film is facing up and the glass side is down before adding 250ml of phosphate buffer pH 6.6 previously equilibrated at 37 + 0.5 o C. The dissolution paddle was rotated at a rate of 50 rpm.This stirring rate is believed to simulate the environment of the buccal cavity.The time taken for the film to completely erode or detach from the mucosa was recorded as the in vitro mucoadhesion time (Hassan et al., 2011).

In vitro release studies
The drug release from the films was studied using USP rotating paddle dissolution test apparatus.The dissolution medium consisted of 250 ml phosphate buffer pH 6.6 containing 0.15% sodium dodecyl sulfate.The later was included to ensure sink conditions.The release studies were performed at 37 + 0.5˚C, at a stirring rate of 50 rpm.Buccal film (4cm 2 ) which contains 10mg of simvastatin was glued to a glass slide with cyanoacrylate adhesive from one side to ensure unidirectional drug release.The glass slide was placed in the bottom of the dissolution vessel so that the film remains on the upper side of the slide.Samples (5ml) were withdrawn at predetermined time intervals (15, 30, 45, 60, 90, 120, 150, 180, 210, 240, 270, 300 min) and replaced with equal volume of fresh dissolution medium.The samples were filtered and analyzed by UV spectrophotometer at 238 nm.The amount of drug released at each time interval was calculated and the cumulative amount of drug released was calculated as a function of time to construct the drug release profile (Hiremath et al., 2009).The drug release efficiency (RE) was calculated from the area under the dissolution curve at time t (determined using the nonlinear trapezoidal rule) and expressed as a percentage of the area of the rectangle described by 100% dissolution in the same time (El Maghraby and Alomrani, 2009).

Compatibility studies of simvastatin with the formulated additives
To investigate any possible interactions between the drug and other ingredients of the formulation, differential scanning calorimetry (DSC) and fourier transform infrared spectroscopy (FTIR) were used.

Differential scanning calorimetry
These studies involved recording the thermograms of the samples (simvastatin, the selected polymers and their films in presence and absence of Tween 80 and/or propylene glycol) using a differential scanning calorimetry (DSC) (DSC-60, Shimadzu, Japan).Samples equivalent to approximately 2 mg of the drug were loaded into aluminum pans before crimping the lids using a Shimadzu crimper.The thermal behavior of each sample was investigated at a heating rate of 10 o C/min, covering temperature ranges of 25-300 o C. The instrument was calibrated with an indium standard.Data analysis was conducted using the TA-60WS thermal analysis software.The transition midpoint (Tm) of the drug was recorded.

Fourier Transform infrared spectroscopy
The Fourier transform infrared (FTIR) spectra of simvastatin, the selected polymers and their films in presence and absence of Tween 80 and/or propylene glycol were recorded using FTIR spectrophotometer (FTIR-Spectrometer, Tensor 27, Bruker, USA).Samples were mixed with potassium bromide (spectroscopic grade) and compressed into disks using hydraulic press before scanning from 4000 to 600 cm -1 .

Physicochemical characteristics of simvastatin buccal bioadhesive films
Table 1 presents the composition of the successful formulations which produced acceptable simvastatin buccal films after solvent casting.The prepared films were transparent, smooth, uniform and flexible.It should be noted that initial studies utilized a formulation similar to F1 but without Tween 80.This produced opaque film which can be attributed to possible precipitation of the drug.This problem was eliminated after addition of Tween 80 to produce F1 which resulted in an acceptable film.It was thus decided to incorporate Tween 80 as a basic component in all formulations.Preparation of PVP-based films F3 was initially prepared in absence of CMC.This resulted in a transparent film which was difficult to remove from the petri dish due to the stickiness of PVP.Accordingly, CMC was combined with PVP and Tween 80 to produce F3 (Table 1) which produced an acceptable film.Incorporation of propylene glycol into the CMC or PVP based films produced plasti films but the films suffered some shrinkage.The same polymers were successfully utilized to prepare buccal films for various drugs.PVP and CMC were incorporated in ketorolac buccal film (Alanazi et al., 2007).Other investigators employed CMC in combination with carbopol to develop clotrimazole buccal film (Singh et al., 2008), with PVP being utilized in combination with hydroxyl propyl cellulose in glibenclamide buccal film (Goudanavar et al., 2010).The physical characteristics of the films are presented in Table 2.The data revealed the formation of thin films with the thickness being increased in case of films containing PG.The increase in thickness can be attributed to the shrinkage of the films.The increase of film thickness was associated with an increase in the weight of the film (Table 2).The recorded values of the thickness and weight are comparable to published data on miconazole buccal film (Rasool and Khan, 2010).Due to the shrinkage of the film the drug content of the shrinked films was more than that of non-shrinked ones.The data in the Table reveal low values of the SD in all parameters which indicates the reproducibility of the method of preparation.The folding and endurance study revealed high flexibility of the films which is indicated from the ability of the films to tolerate folding for more than 200 times without cracking.The microenvironment pH of different batches ranged from 6.05 to 6.84 so they were expected to be palatable.

Swelling index
The swelling index values are in the following order F1> F3> F2> F4 (Table 2).These results suggested that the presence of CMC resulted in stronger water absorption power.This absorption power and hence the swelling index were decreased in presence of propylene glycol and/or PVP.These findings agree with the previously recorded results on similar films (Basu et al., 2010) (Anjankumar, 2011).3.04 (0.31) Values between brackets are SD, n = 3.The swelling index was calculated as the maximum increase in weight relative to the initial weight of the film.The maximum increase in weight was reached after 30, 15, 15 and 10 minutes for F1, F2, F3 and F4, respectively.

Bioadhesion strength and residence time
The bioadhesion strength and time are presented in Table 3.The bioadhesion strength of the prepared film depended on the composition of the film.Films containing PVP showed greater bioadhesion strength compared to the corresponding films in absence of PVP.Thus F3 was better than F1 and F4 was better than F2 with respect to the bioadhesive strength.Similar finding was recorded after incorporation of PVP in CMC films (Perioli et al., 2004).With respect to the effect of propylene glycol on bioadhesion its effect was contrary to that of PVP.This can be explained on the base that the bioadhesion strength depends on the charge density which is higher in case of PVP with incorporation of propylene glycol reducing such density (Habib et al., 2010).It should be noted that the data of bioadhesion time did not correlate with that of the bioadhesion strength (Table 3).This can be attributed to the fact that both parameters depend on different factors with the bioadhesion strength depending on the electrostatic interaction and the bioadhesion time (residence time) being affected by the dissolution rate of the film (Habib et al., 2010).

In-vitro release studies
The in vitro drug release from the prepared films was determined at conditions mimicking the buccal cavity.The release profiles are shown in Figure 1.The kinetics of drug release was determined by fitting the release profiles to the zero-order, firstorder and Higuchi diffusion model.Linear regression was then performed and the correlation coefficient (R 2 ) values were recorded and used for determination of the best fit.These values are presented in Table 4.For CMC based films (F1 and F2) the release pattern followed a zero order kinetics providing constant rate of drug release irrespective to the remaining drug in the film.Incorporation of PVP in the films resulted in films (F3 and F4) which produced initial rapid release followed by slower release rate and the profile followed Higuchi diffusion kinetic model (Table 4).Values between brackets are SD, n = 3.
Similar release pattern was recorded for films containing PVP and/or CMC.For example zero order release pattern was recorded for clotrimazole film in which CMC was used as the polymer (Singh et al., 2008) with CMC/PVP combination producing a film which released ibuprofen according to Higuchi diffusion system (Perioli et al., 2004).The release efficiency was calculated with the goal of investigating the effect of film composition on the release rate of the drug.The calculated release efficiencies are presented in Table 4. Incorporation of PVP in the mucoadhesive films increased the release rate as indicated from the release efficiency values (Table 4).This effect can be attributed to the ability of PVP to increase the wetting and penetration of water into the film matrices with subsequent increase in the diffusion of the drug (Koland et al., 2012).With respect to the effect of incorporation of propylene glycol, its presence increased the release rate which is manifested as an increase in the release efficiency.This can be explained on the base of the solubilizing effect of propylene glycol on simvastatin which can result on faster drug release (Kang et al., 2004).Another possible explanation depends on the humectant nature of the propylene glycol which leads to hydration of the film.This will result in more rapid drug release as the release is known to be proportional to the amount of water absorbed into a film (Rasool and Khan, 2010).

Differential scanning calorimetry
Figures 2 and Figure 3 show representative thermograms for the simvastatin, the selected polymers and their films, in presence and absence of Tween 80 and/or propylene glycol.Pure simvastatin produced sharp endothermic peak at 139 o C corresponding to the melting transition of the drug.This reflects the crystalline nature of the drug.This is in good agreement with previous findings on the thermal analysis of simvastatin (Hiremath et al., 2009).Carboxymethyl cellulose produced broad endothermic peak around 58.315 o C.This broad peak can be attributed to evaporation of the bound water.This thermogram is similar to the previously reported data for the same polymer (Mekkawy et al., 2013).Presence of this endotherm in the thermograms of the films indicates evaporation of the bound water or sorbed moisture.As for CMC, Polyvinylpyrrolidone produced broad endothermic peak at 60 o C.This can be also attributed to evaporation of bound water.This is supported by previous reports on the same polymer (Giri et al., 2010).
Incorporation of the drug in either CMC/Tween or CMC/PVP/Tween films resulted in complete disappearance of the endothermic peak of the drug.This can be attributed to transformation of the drug into amorphous structure or presence of the drug as solid solution in the film.Both films showed the broad endotherm corresponding to evaporation of the bound liquid (Figures 2 and 3).Incorporation of propylene glycol in simvastatin films resulted in the appearance of additional broad endothermic peak with a Tm being recorded in the range of 125 to 134 o C.This broad endotherm can be attributed to evaporation of the propylene glycol which is more viscous liquid.To confirm this explanation, plain films comprising CMC, Tween and propylene glycol with or % Release % Release % Release % Release F1 F2 F3 F4 without PVP were prepared and subjected to DSC study.The resulting thermgrams (Figures 2 and 3) revealed the broad endothermic peaks which were detected in the medicated film.This confirms that the second broad peak corresponds to propylene glycol evaporation.Overall, the recorded DSC data explain the good release rate of such lipophilic drug even in small amount of dissolution medium.

Fourier Transform infrared spectroscopy
Figures 4 and 5 show The FTIR spectra of simvastatin, the selected polymers and their films in presence and absence of Tween 80 and/or propylene glycol.Pure simvastatin showed the characteristics peaks at 3550 which corresponds to the free OH stretching vibrations, 2969 which corresponds to methyl C-H asymmetric stretching, 1699 which is due to the ester C=O stretching and 1269 which is due to lactone -C-O-C stretch.The recorded spectrum is similar to the previously recorded for the same drug (Pandya et al., 2008).
The spectra of pure CMC showed characteristics peaks at 3441.96 which corresponds for the O-H stretching, 2924 which is due to C-H stretch, 1629 corresponding to the anti-symmetric vibration of COO -groups, 1429.49and 1326.55 due to symmetrical deformations of CH 2 and COH groups and at 1056.77 which is due to CH-O-CH 2 stretching.This pattern is in good agreement with the previously recorded spectrum for the same polymer (Tongdeesoontorn et al., 2011).Pure PVP spectrum showed characteristics peaks at at 2994, 2929 and 2835.82due to CH stretching, at 1692.41 due to C=O stretching, 1319.16due to CN stretching, with the peak recorded between 1290.53 and 1017.65 being attributed for the C-H stretching vibration.In addition the spectrum revealed a broad band at 3442.31 which reflects the hygroscopic nature of the polymer.This is similar to the previously recorded spectrum (Giri et al., 2011) (El Maghraby andElsergany, 2014).It is important to note that the critical function groups (carbonyl and hydroxyl groups) are existing in the drug as well as in the tested polymer.
Fig. 4: FTIR spectra of samples (simvastatin, carboxymethyl cellulose and their films in presence and absence of Tween 80 and/or propylene glycol).The curves from top to bottom are pure drug (SIM), pure polymer (CMC), a film composed of (SIM, CMC, and TW), a film composed of (SIM, CMC, and PG), a film composed of (SIM, CMC, TW and PG), and a film composed of (CMC, TW, and PG).
This may make identification of interaction a difficult task.Looking at the spectra of the prepared films, it can be noted that the position of the carbonyl group is in between that of the drug and that of the polymer with the peak becoming broader.Taking into consideration the fact that the concentration of polymer predominate in the film composition, the recorded peak of carbonyl group in the film can be considered as the summation of the peaks of the drug and the polymers.
With respect to the OH stretching vibration of the drug, the recorded band in the films was overshadowed by the corresponding broad bands in the polymers.Overall, the recorded spectra for the prepared films did not reflect significant interaction between the drug and the polymers although it did not exclude possible hydrogen bonding.It should be noted that the release experiments reflected the liberation of the drug from the films suggesting that the presence of hydrogen bonding (if any) is not deleterious for the drug.

CONCLUSION
Preparation of CMC film in absence of Tween and propylene glycol resulted in opaque films due to precipitation of the drug.Incorporation of Tween produced clear film due to solubilization of the drug.Incorporation of PVP into the films increased the bioadhesion force and time.The rate of drug release from the films depended on their composition with presence of PVP increasing the release efficiency compared to the corresponding PVP free films.Similarly, incorporation of PG increased the drug release efficiency.The developed films included the drug in amorphous form or as a solid solution.The developed films are promising for buccal administration.

Fig. 2 :
Fig.2: DSC thermograms of simvastatin, carboxymethyl cellulose and their films in presence and absence of Tween 80 and/or propylene glycol.The curves from top to bottom are pure drug (SIM), pure polymer (CMC), a film composed of (SIM, CMC, and TW), a film composed of (SIM, CMC, and PG), a film composed of (SIM, CMC, TW, and PG), and a film composed of (CMC, TW, and PG).

Fig. 3 :
Fig.3: DSC thermograms of simvastatin, carboxymethyl cellulose, Polyvinylpyrrolidone, and their films in presence and absence of Tween 80 and/or propylene glycol.The curves from top to bottom are pure drug (SIM), pure polymer (CMC), pure polymer (PVP), a film composed of (SIM, CMC, PVP, and TW), a film composed of (SIM, CMC, PVP, and PG), a film composed of (SIM, CMC, PVP, TW, and PG), and a film composed of (CMC, PVP, TW, and PG).

Fig. 5 :
Fig.5: FTIR spectra of samples (simvastatin, carboxymethyl cellulose, Polyvinylpyrrolidone and their films in presence and absence of Tween 80 and/or propylene glycol).The curves from top to bottom are pure drug (SIM), pure polymer (CMC), pure polymer (PVP), a film composed of (SIM, CMC, PVP, and TW), a film composed of (SIM, CMC, PVP, and PG), a film composed of (SIM, CMC, PVP, TW, and PG), and a film composed of (CMC, PVP, TW, and PG).

Table 1 :
Composition of different formulae of simvastatin buccal films.

Table 2 :
Physicochemical characteristics of the prepared simvastatin buccal films.

Table 3 :
Bioadhesion parameters of the prepared simvastatin buccal films.

Table 4 :
Kinetics of simvastatin release of different formulae according to different kinetic models, and the release efficiency.