Formulation and Evaluation of Pulsatile Drug Delivery System of Metoprolol Tartarate Using Core in Cup Tablet

The purpose of this work is to formulate a pulsatile drug delivery system using metoprolol tartarate as model drug. A core in cup (three component tablet) is prepared where in core tablet, an impermeable material surrounding the tablet except the top and soluble hydrophilic polymer layer at the top is designed. The core tablet contains metoprolol tartarate, cellu lose acetate propionate is used as impermeable membrane and sodium alginate 500 cps and sodium alginate 2000 cps used as soluble hydrophilic polymer layer .The top cover layer is prepared using 3 factorial design. Quantification of water uptake, top layer expansion, in-v itro dissolution studies, radial and axial expansion, stereomicroscopic image, and short term stability studies are performed. The concentration of top layer of hydrophilic polymer is a critical factor governing the release pattern, increase in the concentration increased lag t ime and delay the release .The T70% and T90 % values are also influenced by the polymer concentration with less polymer concentration of hydrophilic polymer lesser T70% and T90 % values are obtained and as the concentration increased higher values are obtained. It can be concluded from the study that pulsatile drug delivery system useful in chronotherapy of hypertension can be prepared by this technique.


Introduction
Chronotherapy refers to treat ment in which the availability of the drug to the body can be tailored to meet the therapeutic requirement. Earlier the development of the drug delivery system was based on the homeostatic theory according to this theory biological functions are constant over time however chronobiological studies contradict this theory, nearly all functions of the body including those influencing pharmacokinetic parameters display significant variat ion. Circadian or 24 hrs rhythm exists in blood pressure, blood flow, stroke volu me, peripheral resistance, gastric acid secretion, gastro intestinal motility and gastric emptying as in [1] . . Co mmon symptoms of allerg ic rh initis such as sneezing, nasal rhinorrhea, red itchy eyes were found to occur most frequently in the morning and least frequently in middle of the day as in [2].
Circadian rhythm exists in arthrit ic pain and patients with rheu mato id arth ritis experience g reat pain in the early morn ing and patient with osteoarthritis have more pain in the evening hours as in [3]. In cardiovascular diseases capillary resistance and vascular reactivity are higher in the morning and decrease latter in the day, platelet agreeability is increased leading to state of reactive hypercoagulability of the blood because of this reaction the frequency of myocardial infarct ion and sudden cardiac death are more prone in the morning. A mbulatory blood pressure study also con firmed the presence of circadian rhythm as in [4]. Pulsatile drug delivery system is a controlled drug delivery system where drug is released after a preprogrammed lag time. Various approaches have been used to design a pulsatile release formu lation, erodib le devices provided with hydrophilic poly mer coating are widely used and such a system when exposed to dissolution med iu m undergo swelling, d issolution and/or erosion. Lag time in such a system can be controlled by using various hydrophilic poly mers such as HPMC, polyethylene o xide, sodium alginate, sodiu m CM C. The concentration and viscosity of these poly mers play a significant role in controlling the lag t ime and release pattern as in [5].
A Capsular system in wh ich the body part coated with impermeab le poly mer and hydrophilic matrix plug sealing the drug formulat ion is used to prepare pulsatile drug delivery system. Upon contact with aqueous fluids a rapid dissolution would occur and plug undergoes a gradual swelling and finally exp luded fro m the body thus allowing the drug to release. The lag time in such formu lation is controlled by the time needed for the p lug removal and its duration depends on the physical, chemical nature, size and position of the plug. On the other hand an insoluble plug and semi permeable capsule body containing active ingredient is also used, the influ x o f water into capsule would lead to surge in its internal pressure ultimately resulting in plug expulsion and drug release as in [6]. Os motic pu mps are also used to achieve pulsatile release fro m the formu lation.
Metoprolol tartarate is selective beta adrenoreceptor blocking agent used to treat hypertension, angina and heart attack.
The aim of the present work is to develop a simple one pulse drug delivery system based on dry coated tablet preparation. The system consist of a core tablet containing the drug, an impermeable outer shell and top cover layer barrier that dissolves at predetermined time. Cellu lose acetate propionate is used as insoluble material and a blend of sodium alg inate 500 cps and sodium alginate 2000 cps used as hydrophilic top layer. The hydrophilic poly mers concentration is selected using 3 2 factorial designs to get the desired pulsatile release. The drug is released after removal of top layer of hydrophilic poly mers and the lag time being adjusted by properties of the material in top cover, metoprolo l tartarate is used as model drug

Material and Methods
Metoprolol tartarate is received as gift sample fro m Torrent research centre Ah madabad, cellulose acetate propionate is purchased from Arcos Organics New Jersey USA. Sodiu m alginate 500 cps is purchased fro m Finar Chemicals Ltd Ahmadabad and Sodium alg inate 2000 cps is purchased from loba chemie Mu mbai.  The tablets are prepared based on 3 2 factorial design, concentration of Sodiu m alginate 500cps and Sodium alginate 2000 cps are selected as two independent variable .Three level determined fro m preliminary studies of each variable are selected and totally 9 batches are prepared Table 1. The tablets are co mpressed using Karnavati minip ress and the system consists of core in cup tablet. The core tablet is prepared with 100 mg of metoprolol tartarate using 7 mm punches further 9 mm punches are used to prepare core in cup tablet. Cellulose acetate propionate 100 mg is placed at the bottom and gently compacted to make powder bed, core tablet is placed at the centre and impermeab le cellu lose acetate propionate 65 mg is placed at the sides of the tablet so that surrounding surface of core tablet was fully covered. On the top a blend of hydrophilic soluble polymer material (sodium alg inate 500 cps and sodium alginate 2000 cps) is placed and finally comp ressed to get a core in cup table.

FTIR and DSC Studies
The formu lation is subjected to FTIR and DSC studies to determine the compatib ility of drug and excipients.

Pre Compression Parameters
The pre compression parameters evaluated include bulk density, tapped density, hausner's ratio,carr's index and angle of repose.

Post Compression Parameters
Post compression parameters evaluated are thickness, hardness, friability, weight variation of the tablets. Further the tablets are subjected to the following evaluation parameters.

Drug Content Esti mation
Five tablets are taken and crushed, drug equivalent to 100 mg is placed in a stoppered 100 ml conical flask and drug is extracted with 25 ml of phosphate buffer PH 7.4 and filtered into 100 ml volu metric flask through Whatman No.1 filter paper (Mean pore diameter 1.5 µm) and volu me is made up to 100 ml. Aliquots of the solution are filtered and analy zed for drug content by measuring the absorbance at 225 n m.

Quantification of Water Uptake
For studying the water uptake the dissolution beakers are ma rked with time points 0.5, 1, 1.5 up to 6.5 hours. One tablet is placed in each of the marked dissolution beakers containing Phosphate buffer PH 7.4 maintained at 37±0.5℃ and stirred at 50 rp m. The tablets are removed fro m the beaker after co mplet ion of the respective time and the excess water present on the surface is removed with the help o f the filter paper the tablets are weighed on shimad zu digital balance. The increase in weight of the tablet reflects the water uptake. It is estimated by equation Q=100 (Ww-Wi)/Ww Where Q = the percentage of liquid uptake and Ww and Wi are the mass of the hydrated sample and initial starting dry weight respectively. M etoprolol Tartarate Using Core in Cup Tablet

3.6.Top Cover Layer Expansion
The purpose of this study is to observe the top cover layer expansion and correlate with the lag time and drug release of the formulation. The tablet is attached to microscopic slide with adhesive and edges of the microscopic slides are t ied with a thread and placed in a d issolution beaker (dissolution apparatus) containing 900ml of phosphate buffer PH 7.4 maintained at 37±0.5℃ and stirred at 50 rp m. At every 30 min interval the microscopic slide is withdrawn fro m the dissolution beaker with the help of the thread t ied to the slides. The tablet is photographed using Samsung digital camera (NV 20) to study the top cover layer expansion and observe the influence of hydrophilic polymers on the lag time and release pattern.

In-Vitro Drug Release
Dissolution studies of metoprolol tartarate is carried out in phosphate buffer PH 7.4 maintained at 37±0.5℃ using USP XXIII tablet d issolution test apparatus-II (Campbell electronics DR-6 d issolution apparatus) at 50 rp m. 5ml samples are withdrawn every 30 minutes filtered and analyzed at 225 n m using PG instruments UV-Visib le spectrophotometer, equal volu me of dissolution med iu m is replaced immediately.

Radial and Axial Measurement
The aim of the study is to measure the radial and axial expansion because of swelling. A tablet is attached on a microscopic slide with adhesive and both ends of slides are tied with thread and further it is placed in the dissolution beaker wh ich contained phosphate buffer PH 7.4 maintained at 37±0.5 ℃. The slide is removed fro m the dissolution beaker at every 30 min with the help of thread and increase in diameter and thickness is measured with the help of scale

Statistical Analysis
Response surface modeling and statistical analysis are performed using (PCP d isso 200 V3 software designed by Bharati vidyapeeth Poona college of Pharmacy). 3D plots and contour plots are constructed using the same software

Stereomicroscopic Studies
The prepared tablet contains three component insoluble polymer layer at the bottom and surrounding the core tablet, core tablet at the centre and hydrophilic swellab le poly mer at the top. To study the inner arrangement of the assembly the tablet is cut vertically at the centre and photographed using stereomicroscope.

Stability Studies
Short term stability studies are performed at a temp of 40±2℃ and 75±5 % RH over a period of three months(90 days).The tablets of the best formulat ion are placed in stability chamber(Thermal instruments and equipments) and samples are withdrawn every month visually examined and evaluated for drug content and in-vitro dissolution studies.

FTIR and DSC Studies
In the present study the drug used is metoprolol tartarate, since the drug contain tartaric acid salt it gives a broad absorption peak around 3450 cm -1 corresponding to hydroxyl group of the drug as well as hydroxyl group of tartaric acid residue. It also contains aromat ic C-C-H and aliphatic C-C-H which is indicated by the absorption peak at 2980 cm -1 and 2872 cm -1 . The N-H absorption peak of the drug as merged with the hu mp is observed at 3150 cm -1 , the IR o f this compound also exh ibited peak at 1690 cm -1 and 1632 cm -1 corresponding to the carboxylic acid residue of tartaric acid. All the data obtained fro m the IR spectrum are in agreement with the known structure of the metoprolol tartarate. The above drug is subjected to formulation with different excip ients. In cellulose acetate propionate a weak absorption is noticed at 3497 cm -1 probably because of free hydroxyl group present in the moiety. The C-C-H of the type which is part of the ring structure of the sugar or C-C-H of the alkyl residue attached to the hydroxyl group are noticed at 2982 cm -1 and 2944 cm -1 respectively. The ester moiety of acetate as well as propionate have exh ibited strong absorption peak at 1743 cm -1 which is the normal place of absorption of carboxy l esters.
Sodiu m alginate contains number of hydroxy l g roup of primary and secondary nature and hence IR spectrum of this compound gave a broad hump at 3400 cm -1 where in primary as well as secondary hydroxyl group absorption peak have been merged to g ive rise to a hu mp. It is noticed that only aliphatic C-C-H absorption peak are noticed in the IR spectrum suggesting that it has no aromatic residue. The sodium salt of carboxylic acid residue present in the mo lecule has also exh ibited a broad peak at 1610 cm -1 these are the characteristics peak noticed for sodium alginate A core in cup pulsatile drug delivery system of metoprolol tartarate is formu lated and the formu lat ion obtained is taken for IR measurement. The formu lation contains metoprolol tartarate, cellu lose acetate propionate and sodium alginate, the IR spectrum of the formu lation exhib ited a weak absorption peak at 3480 cm -1 and a peak at 3150 cm -1 due to the O-H and N-H of the drug mo iety. The presence of C-H due to the aromatic C-H and aliphatic C-H observed at 2980 cm -1 and 2872 cm -1 , the strong peak are observed at 1739 cm -1 and 1632 cm -1 due to the ester group of the cellu lose acetate propionate. The data obtained suggests that all the characteristic functionalities of the drug and the excipients have remained unchanged during the process of formulat ion, confirming that no chemical reaction has taken place.
The drug metoprolo l tartarate is subjected to DSC measurements in which it starts melting at 121.23℃g iving rise to melting peak at 124.26℃ this is because pure drug is not used its salt is used and because of this broad melting range is observed but not the Sharpe.
The formulation is subjected to DSC studies, the melt ing range is obtained at 123.14 ℃ and 66.58 ℃ thereby suggesting that drug and excipients have given rise to melting range 123.14 ℃ and 66.58 ℃ . The reduction in melting range of the drug by 1℃ is due to the preparation of physical mixture during the formu lation. This strongly suggests that drug has remained intact and not under gone any chemical change during the formulat ion process A core in cup tablet for Pulsatile release of metoprolol tartarate is prepared. A total of 9 fo rmulat ions are prepared by keeping the concentration of drug and impermeab le layer constant, soluble hydrophilic poly mer concentration is selected by using 3 2 factorial design.

Pre Compression Parameters
The bulk density is in the range of 0.64 g/cc to 0.68 g/cc and tapped density in the range o f 0.75g/cc and 0.79 g/cc, carr's index in the range of 12.80 % to 15.18 %, hausner's ratio in the range of 1.14 to 1.17 and angle of repose in the range of 24.18 to 26.24 degree as shown in Table 2. It can be concluded from the study that formulat ion has good flow property and can be compressed into a tablet which meets all the requirements.

Post Compression Parameters
The appearance of the tablets is smooth and uniform, hardness of the tablets is in the range of 5.5 to7.0 kg/cm 2 , thickness in the range of 5.5 to 6.5 mm, weight variation in the range of 3 to 4 % and drug content in the range of 98.40 to 99.82 %.
The prepared pulsatile drug delivery system has three parts a core tablet, impermeab le layer and soluble hydrophilic top layer consisting of sodium alginate 500 cps and sodium alginate 2000 cps used in 3 2 factorial design .The top hydrophilic layer in the fo rmulat ion is designed to absorb water and swell when it gets in contact with liquid, after swelling a gel layer is formed around the tablet which acts as a barrier that prevents the liquid fro m reaching the core surface. In total 9 formu lations are prepared and the tablet with less amount of poly mer on top layer achieved less swelling when co mpared to tablets having higher concentration of polymer on top layer. Visual observation shows a greater swelling for SA9 formu lation with poly mer ration (+1,+1). Thus from the study it is observed that the top cover layer swelling and lag t ime are influenced by polymer concentration and viscosities.  Swelling of the polymer is an crit ical aspect governing the release pattern, the process starts immediately when the tablet gets in contact with liquid as shown in Figure 1/ Figure  2 three formu lation are selected to understand the swelling process and its influence on lag t ime and release pattern. SA1 with low concentration of poly mer (-1,-1), SA 5 with mediu m concentration of polymer (1,1) and SA 9 with high concentration (+1,+1) are selected. Visual observation indicates formation of a gel layer at the top of the tablet when exposed to liquid, formu lation SA9 exhib ited higher extent of swelling in co mparison of other two formu lations.
In SA1 maximu m swelling is obtained at 2.0 hrs and after reaching maximu m swelling a gradual reduction in swelling is observed , the swelling process is terminated at 3.5 hrs. In SA5 maximu m swelling is observed at 3 hrs and the process is terminated at 4.5 hrs and in case of SA9 maximu m swelling is observed at 4.0 hrs and the swelling process is terminated at 6.5 hrs. SA1 achieved maximu m swelling of 58.31%, SA5 M etoprolol Tartarate Using Core in Cup Tablet achieved maximu m swelling of 61.34 % and SA9 achieved maximu m swelling of 66.69 % respectively. Reduction of swelling is faster in case of SA1 followed by SA5 and SA9. The lag time obtained in SA1 is 2.5 hrs which corresponds to time point 2.0 hrs where decline in swelling has started, in SA5 the lag t ime obtained is 4.0 hrs wh ich corresponds to maximu m swelling point 3.0 hrs and finally in SA 9 lag time obtained is 5.0 hrs wh ich corresponds to maximu m swelling point 4.0 hrs. The formu lation SA9 with high concentration of poly mer is selected for the study. Figure 3 demonstrate changes in top layer, 30 minutes time interval is selected in order to observe the changes that occur in top hydrophilic layer upon contact with liquid. After contact of tablet with liquid a fast absorption of liquid takes place and the poly mer starts to swell as shown in Figure 3 (0.5 hr) as the t ime proceeds mo re swelling takes place and after reaching a maximu m swelling a gradual decrease of polymer mass is noticed and this is more obvious after 4.5 hrs coincid ing with this at 5 hrs the top polymeric layer is dilute enough to initiate the drug release as shown in Figure 3(5.0 hrs) / Figure 4. The poly mer after init ial swelling retains its intensity for a particular period and then starts reduction in its mass at 6 hrs 20.62 % drug is released and after 6.5 hrs the top layer is co mp letely separated and 39.32 % o f drug is released and with time mo re amount of drug is released and at 10.5 hrs 99.14 % of drug is released

Radial and Axial Expansion Measurement
SA1, SA5 and SA9 formulat ions are selected to study radial and axial expansion due to swelling three formu lation contained low, mediu m and high concentration of poly mer on top layer.
In SA1 the init ial d iameter is 9 mm and maximu m rad ial expansion of 10 mm (1.1 fold) is observed at 1 hr time interval followed by a gradual decrease, in SA5 the initial diameter is 9.5mm and maximu m radial expansion of 11.5 mm(1.2 fo ld) is observed at 2.0 hrs and in SA9 the initial diameter is 9 mm and maximu m rad ial expansion of 12.5 mm (1.4 fold) is observed at 2.5 h rs.
The axial (thickness) expansion is also measured in SA1 the initial thickness is 5.5 mm and maximu m axial expansion of 12 mm (2.1 fold) is observed at 2.0 hrs, in SA5 the init ial thickness is 6.0 mm and maximu m axial expansion of 15.5mm (2.6 fold ) is observed at 3.0 hrs and in case of SA9 the initial thickness is 6.0 mm and maximu m axial expansion of 17.5mm (2.9 fo ld) is observed at 4.0 hrs respectively. The study confirms the preferential axial expansion, the polymer swells more in axial d irection co mpared to rad ial d irect ion.

Statistical Analysis
In order to investigate the factors systematically and to arrive at an optimu m fo rmulat ion a 32 factorial design is emp loyed in the present investigation. A polynomial equation is derived for the lag time and T 70% (t ime required for 70% of drug release) using PCP d isso 2000 V3 software (developed by Bharati vidyapeeth's Poona college of Pharmacy). The studied factors(independent variable) are concentration of sodium alg inate 500 cps, sodium alginate 2000cps and the response ( dependent variable) studied are lag time and T 70%.
A second order polynomial equation that fitted the data is as follows Y=b 0 + b 1 X 1 + b 2 X 2 + b X 1 X 2 + b 11 X 1 Where Y is the independent variable bo is the arith metic mean response of nine batches, b 1 ,b 2 , b 11 b 12 and b 22 are coefficient computed fro m the observed experimental values X 1 and X 2 stand for main effect and the polyno mial terms X 1 2 and X 2 2 are included to investigate the non linearity.
The reduced model with significant values for both the factors are Lag time Y1 = 3.777 + 0.916 + 0.250 T 70% Y2 = 5.818 + 1.461 + 0.513 Positive sign in front of the term indicate synergistic effect while negative sign indicate antagonist effect of the factor as in [10]. The positive sign observed in the present study indicated synergistic effect and as the concentration of polymer increase the lag t ime is increased and the time required for T 70% drug release is also is increased, the p value less than 0.05 observed indicant the significance effect.

Res ponse Surface Analysis
The quadratic models generated by regression analysis are used to construct 3D response surface plots. A linear synergistic effect between two independent variable on response is observed. Figure 6    To study the inner assembly of the three co mponents, the tablet is cut vertically at the centre and photographed using stereomicroscopy. The images Figure 10 clearly shows three components a insoluble poly mer at the bottom and surrounding the tablet except the top, core tablet at the centre and soluble hydrophilic poly mer at the top of the core tablet.
The images confirm the proper positioning of the core tablet in the assembly. Further the formu lations are subjected to goodness of fit test by linear regression analysis according to zero order, first order, higuchi and peppas model. R values of all the formulat ion were in the range of 0.810 to 0.906 indicat ing a zero order release as shown in Table 4.

Stability Studies
The formulation SA9 is subjected to short time stability studies for 3 months ( 90 days) at 40±2℃ and 75±5 % RH . Samples are withdrawn every month and analyzed for drug content and invitro release. The drug content and dissolution data of the stability studies does not show any significant variation as shown in table 5/ Figure 11.  11. In-Vitro drug release studies of formulation SA

Conclusions
Core In cup pulsatile drug delivery system of metoprolol tartarate is formu lated to increase the therapeutic effectiveness of the drug. The formulat ion contains three components a core table, impermeable layer and soluble hydrophilic poly mer layer. The in-vitro dissolution studies indicates drug release after lag time and the lag t ime is controlled by the soluble hydrophilic poly mer concentration and its properties. The lag time is increased by increasing the concentration of poly mer. The formu lation SA 9 with (+1,+1) concentration of sodium alginate 500 cps and sodium alginate 2000 cps gave a lag time of 5hrs and 99.14% of drug release in 10.5 hrs. Thus the drug release fro m the tablet can be tailored to meet the therapeutic requirement of the patients.
The formulation with greater concentration of soluble hydrophilic poly mer swells to a greater extent and hence the swelling rate is directly proportional to the polymer concentration. Formulation SA9 shows a greater swelling compared to other formu lation.
FTIR and DSC studies confirm that the drug and polymer are co mpatible with each other.
Short term stability studies indicate no significant changes in drug content and dissolution rates. Thus with this system a pulsatile drug delivery system can be prepared to increase the therapeutic effectiveness of the drug.