FORMULATION AND BIOPHARMACEUTICAL EVALUATION OF SUSTAINED RELEASE PELLETS OF BOSENTAN BY PANCOATING METHOD

Objective: The aim of the present study was to formulate sustained-release pellets of bosentan by eudragit RL 100 and RS 100, which are the polymers used in the pan coating technique. Methods: The sustained release pellets of bosentan were formulated by pan coating method. The drug was coated on nonpareil seeds along with EudragitRL100 by solution layering technique. Drug-loaded pellets were coated with EudragitRS100. The prepared pellets were evaluated for moisture content, drug content, particle size, and in vitro drug release. Stability studies were carried out on the optimised formulations for a period of 6 mo. Results: The drug content was in the range of 98.89±0.32. The mean particle size of the drug-loaded pellets was in the range of 835 μm. The drug release rate decreased as the concentration of eudragit increased in the pellet formulations. Among the prepared formulations, PC 4 showed 89.35±0.52 drug release in 12 h from a good linear relationship was established between model-independent approaches (T25%, T50%, and T100%) and weight gain in coating. This indicated the possibility of extending the drug release by increasing the weight gain in the coating, and hence, it was proposed to extend the drug release for 24 h. From the prepared pellets, the optimised formulation PC 12 showed a 100.02±0.03 drug release in 24 h. Furthermore, these pellets were filled into capsules and compared the dissolution studies. The compatibility between drugs and polymers in the drug-loaded pellets was confirmed by DSC and FTIR studies. Stability studies indicated that the pellets were stable . Conclusion: The prepared pellets were capable of releasing the drug for 24 h to treat the Pulmonary Arterial Hypertension.


INTRODUCTION
Pulmonary arterial hypertension is a severe condition marked by an increase in pulmonary vascular resistance, which can lead to right ventricular failure [1].Scleroderma patients can develop pulmonary arterial hypertension in up to 50% of cases [2].Long-term anticoagulant therapy and calcium-channel blocker therapy are two of the few oral treatment choices, the latter improves survival in a small number of individuals [3,4].Continuous intravenous infusion of epoprostenol (prostacyclin) has been shown to have beneficial effects, but it also has limitations [5].The effectiveness of epoprostenol analogues that can be inhaled (e. g., iloprost) or given orally (e. g., beraprost) is still determined [5][6][7].Endothelin-1 appears to play a harmful role in pulmonary arterial hypertension, with evidence that blocking endothelin receptors may be helpful [8,9].Endothelin-1 is a powerful endogenous vasoconstrictor and smooth-muscle mitogen that is overexpressed in patients with primary pulmonary hypertension and scleroderma's plasma and lung tissue.Two receptors, ETA and ETB, are involved in its activities [5].Bosentan is the first Endothelin Receptor Antagonist (ERA) to be used successfully in the treatment of Pulmonary Artery Hypertension (PAH).It is a non-peptide, orally active, dual endothelin receptor antagonist [10].
The drug of choice in this study was bosentan its oral bioavailability is 50% [11], biological half-life is 5 h [12].Due to low bioavailability and less biological half-life need to be given frequent administration to maintain plasma levels effectively.Hence, the drug works best when plasma fluctuations are kept to a minimum; the sustainedrelease dosage form of bosentan is appealing, which makes it ideal for the development of sustained-release formulations.

Materials
Aurobindo Pharma, Hyderabad, provided a complimentary sample of bosentan.This study employed isopropyl alcohol, acetone and dibutylphthalate, which were purchased from Qualigens chemicals, India.Eudragit RL100 and eudragit RS100 were purchased from Loba Chemicals, India.All other chemicals were of analytical grade.Prior approval by the Institutional Animal's Ethics Committee was obtained for conducting the experiments (IAEC/BS/22/CLPT/dated: 08-05-2023).

Calculation of initial dose and maintenance dose for the design of sustained release DDS of bosentan for 12 h
There are no sustained release formulations for bosentan in the market; hence the total dose (DT) consisting of initial (DI) and maintenance doses (DM) for formulating the bosentan sustained release was calculated as per Robinson and Eriksen equation with zero order release principle [13][14][15].

Evaluation of coated pellets
The resulting pellets were assessed for percent yield, drug content estimation, moisture content, angle of repose, bulk density, tapped density, friability, and particle size before being tested in vitro.

Calculation of percent yield
The percentage yield is the difference between the actual quantity of coating applied to the pellets and the theoretical amount of coating applied.It might be the result of too much soaking or drying.A yield of greater than 90% was considered satisfactory.The % yield was calculated using the formula [16].
%yield= Practical yield ofpellets Theoretical yield of pellets ×100 Estimation of percent drug content 100 mg of pellets were weighed and pulverised in total.The powder was completely dissolved in 100 ml of methanol: 0.1N HCl (60:40).The absorbance was measured using a UV spectrophotometer at 272 nm against a blank after the sample was filtered and diluted properly.The proportion of drug content was calculated.The experiment was carried out three times, with the average findings being recorded [17].

Moisture content
The residual water content in the coated pharmaceutical pellets was measured using a Karl Fisher titrator.Crushed pellets totalled 3 g.Then, 0.5 g of the test sample was transferred to the titration tank of the Karl Fisher titrator and titrated to the endpoint with Karl Fisher reagent.
Using the equation below, the moisture content was calculated [18].
Where V= Volume in ml of Karl Fisher reagent consumed for sample titration.
F= Factor of Karl Fisher reagent.

Determination of micromeritic properties of coated drug pellets
Angle of repose, bulk density, and tapped density of the coated pellet s were all evaluated [19].

Angle of repose
Pellet flow parameters were studied using the fixed funnel and freestanding cone techniques [20].

Bulk density
Bulk density is defined as the quantity of powder/granules divided by the volume of the loose powder bed/granules.The unit volume refers to both the space between the particles and the envelope volume of the particle.The bulk density was estimated using a graduated cylinder technique [21].

Tapped density
The tapped density is the ratio of the mass of the powder/granules to the volume occupied by the powder after a particular number of taps.
The tapping density of the pellets shows their dense random packing.

Friability
Pellets must be durable enough to survive the physical pressures of manufacture and transportation.6.5 g of coated pellets samples were pre-weighed in the Roche friabilator's spinning chamber.Pellets were subjected to 100 six-inch falls (25 rpm for four minutes).After the rotation was complete, the pellets were dedusted and reweighed.The percentage of friability was calculated using this formula [22].

Particle size determination
The average particle size of pellets was determined using sieve analysis.The sample collection and sieves were layered with the biggest mesh apertures on top and the smallest mesh apertures below.A sieve shaker was filled with 100 g of coated pellets and a series of sieves (#14, #16, #18, #20, #25).All of the sieves were removed after ten minutes, and the weight of the retained pellets on each sieve was determined.On each filter, the average particle size and % weight retained were determined [23].

In vitro dissolution study
The USPXXIV apparatus was used to investigate the in vitro dissolving of pellets.The first two hours of dissolving were done in 900 ml of 0.1N HCl, followed by the remaining hours in pH 6.8 phosphate buffer.The temperature in the centre was adjusted at 37 °C+0.5 °C.In the dissolving vessel, bosentan pellets containing 74 mg were inserted with the paddle moving at 50 rpm.5 ml of material was collected at predetermined intervals and replaced with the same volume of fresh media.The samples were filtered using a 0.45 m membrane filter.The samples were examined using a UV spectrophotometer.The drug release experiments were repeated three times, with the average cumulative percentage of drug released being recorded each time.Drug release from a commercial immediate-release formulation of bosentan tablet (Bosentas 62.5, a product of Cipla, India, Batch No: G28257, Mfg.Date: 12/2022, Exp.Date: 11/2024) was examined using 900 ml of 0.1 N HCl as the dissolving medium [24].

Establishment of drug release kinetics and mechanisms
The amount of medication released from pharmaceutical dosage forms and the methods by which it is released are crucial but difficult processes that are readily apparent in matrix systems.
Zero-order [25] or first-order kinetics [26,27] were used to characterise the sequence of drug release from matrix systems.The Higuchi diffusion model [28] and the Hixon-Crowell erosion model [29] were used to investigate the mechanism of drug release from matrix systems.The Korsmeyer-Peppas equation was also utilised to distinguish between Fickian/non-Fickian/anamolus drug release mechanisms [30,31].The release exponent 'n' value is used to define distinct release processes for a dosage form, according to the Korsmeyer-Peppas equation.

Stability studies of the optimized formulations
The study employed the ICH's Zone VI guiding principles.The capsules were kept in a polyethylene-lined aluminium container.The aluminium pack was then securely closed.The pack was stored in a humidity chamber for at least 6 mo, with the temperature set at 302 °C/705% RH for long-term conditions and 402 °C/755% RH for expedited settings.The product is considered stable when no significant changes are discovered during stability tests.6 mo of stability data is sufficient for long-term research where there is no discernible change under accelerated conditions2.Moisture content, drug content, and an in vitro dissolution investigation were all performed on the samples [32].

In vivo evaluation of bosentan sustained release pellets and commercial product
Drug development currently includes bioavailability and pharmacokinetic investigations of newly discovered formulations.
The researchers' goal is to investigate the bioavailability of the newly produced formulations [33].

Products tested for in vivo evaluation
The following products were studied in vivo pharmacokinetically.

Experimental design for pharmacokinetic evaluation
Adult male albino rabbits weighing 2.5±0.56 kg were taken.The rabbits were kept in normal cages in an animal room with air, humidity, and temperature control, as well as a 12-hour light/12 h dark cycle.Rabbits were given free access to ordinary home chow and water.The animals were admitted to the animal house conditions at least one week before the inquiry began.
Three groups of rabbits were formed, each with two rabbits.The trial was repeated three times using a one-week washout interval between treatments and a single dosage crossover design.Before receiving the experimental formulations, the rabbits were fasted for at least 10 h (overnight).One hour after receiving the experimental formulations, they were permitted to drink water.Four hours after the medicine was administered, the animals were given access to the diet.

Pharmacokinetic evaluation of the selected products
A wooden rod was put between the rabbit's jaws to prevent the mouth from closing, and a gastric intubation tube (4 mm) was introduced into the stomach.
Group I administered a 2 ml suspension of commercial tablet powder followed by a 10 ml water wash.Group II took FC6 pellets that were comparable to the rabbit's dosage and were rinsed down with 10 ml of water.The treatments were repeated in all of the groups with a one-week washout period in between.

Collection of blood samples
Approximately 0.8-1.0 ml of blood was taken from rabbits' marginal ear veins and placed in pre-labeled 2 ml K2 EDTA-coated tubes.Blood samples were taken at regular intervals before and after the dosage.We took samples at 0, 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, 12, and 24 h.After collection, the blood samples were centrifuged at 3000 rpm for 10 min.The supernatant plasma was separated and kept at-20 °C until analysis in appropriately labelled containers.250 litres of plasma were collected and estimated.

Assessment of pharmacokinetic parameters
Using plasma drug concentration data, non-compartmental analysis was used to calculate all relevant pharmacokinetic parameters such as peak plasma concentration (Cmax), time at which Cmax occurred (Tmax), elimination rate constant (Kel), biological half-life (t1/2), absorption rate constant (Ka), area under the curve (AUC), and mean residence time (MRT).The plasma concentration-time profile was used to determine the maximum plasma concentration (Cmax) and time to attain maximum plasma concentration (Tmax).Values are expressed in (mean±SD., n=3)

Model-independent approaches
A good linear relationship was established between modelindependent approaches (T25%, T50% and T100%) and % weight gain in coating.This indicated the possibility of extending the drug release by increasing the %weight gain in coating and hence, it was proposed to extend the drug release for 24 h.Accordingly, the initial and maintenance doses of bosentan were calculated employing the similar approach adopted for 12 h release.

Calculation of initial dose and maintenance dose for the design of sustained release drug delivery systems of bosentan for 24 h
The initial (DI) and maintenance doses (DM), was calculated using th e Robinson and Eriksen equation with the zeroorder release principle according to above procedure [13][14][15].
The obtained initial dose = 37.

Method of preparation
Based on theoretical predictions, Nonpareil seeds (200 mg) will be coated with 135 mg of the drug and 3.5 mg eudragit RL100 i.e., 338.5 mg (equivalent to 135 mg of bosentan dose).The drug-loaded pellets will be coated with 10% eudragit RS100 polymer solution with plasticizer dibutyl phthalate to achieve a percentage weight gain in coating in the range of 17.5-30%.The formulation will be optimized based on drug release for 24 h.Coated pellets equivalent to 135 mg (based on drug content) from optimized formulation will be filled in to a suitable size of capsule.q. s. q. s. q. s. q. s. q. s. q. s.Total weight (mg) 338.5 338.5 338.5 338.5 338.5 338.5

Evaluation of coated pellets
The resulting pellets were assessed for percent yield, drug content estimation, moisture content, angle of repose, bulk density, tapped density, friability, and particle size before being tested in vitro.

Percentage yield
Among all formulations, PC12 has achieved highest percent yield (96%) and PC11 has achieved lowest percentage yield (90%) which indicated that every formulation has received satisfactory level of coating.

Drug content
Drug content of pellet formulations (PC7-PC12) was found to be 85 to 98%, which revealed that the drug content was within the limits prescribed by I. P.

Moisture content
Percentage moisture values for all the prepared coated pellets were found to be in the range of 1.25% to 2.47%.From the results no significant percent moisture content was observed.

Micromeritic properties
The bulk density tapped density for all the formulations were found to be less than 2 g/cm3.The angle of repose values were in the range of 11.48° to 19.32°.The results of the micromeritic properties indicated excellent flow properties for pellets, which may be due to the spherical shape of the pellets.

Friability
The percentage weight loss in the friability test was found to be less than 1% for the all the formulated batches.It indicated the ability of the pellets to withstand abrasion in packing, handling and shipping.
The evaluated test observations are shown in table 9

Particle size determination
According to experimental findings the average particle size was found to be 835 µm.Overall, 90% of the pellets were obtained in the desired particle size range proving that the process is very reproducible.

In vitro dissolution studies
In vitro dissolution studies showed that 5-10% of drug was released in one hour.The results indicated that increased coating weight decreased the drug release [24].This was observed in all the formulations.The formulations PC7, PC8 coated with 17.5%, 20% of weight gain pellets released 25% of the drug within 2 h.Formulations PC9, PC10 coated with 22.5%, 25% of weight gain pellets released 25% of the drug in 4-5 h.Formulations PC11, PC12 coated with 27.5%, 30% of weight gain pellets released 25% of the drug in 5-6 h.

Drug release kinetics
The zero and first order correlation coefficient (r) values of PC7 to PC12 are presented in table 10.In all the cases the appropriate correlation coefficient (r) values were in favor of zero order release rather than the first order release [25].

Optimization of formulation
Based on physical properties like friability, drug content and % yield formulation PC12 showed high desirable values, which indicated more suitability of formulation for extending the drug release over a period of 24 h.
The dissolution profile of optimized formulation was compared with the theoretical profile.Comparative release profile is shown in table 12 and fig. 5. To confirm the matching of dissolution with the theoretical profile f1 and f2 values were calculated.Optimized formulation f1 was<15 and f2 value was more than '50' (table 9) indicating the similarity between the optimized formulation and theoretical profile.The results clearly indicated that the optimized formulation followed zero order release kinetics with diffusion mechanism as per the predicted theoretical release rate confirming the suitability of the predicted theoretical release profile.PC12 pellets equivalent to 135 mg of bosentan were taken for preparation of each capsule i.e. 440 mg.Avicel PH101 (microcrystalline cellulose) and magnesium stearate as glidants.All the ingredients were mixed sufficient for 30 capsules and mixed in a polybag and filled into capsule size '0' using hand filling capsule machine.
The formula of the prepared capsules is shown in table 14.

Table 1 : Predicted theoretical drug release profile
added and continued stirring for another 10 min.The concentration of plasticizer is 20% of polymer concentration, which was decided based on the pre trials conducted.The composition of the coating solution is shown in table3.

Fig. 1: Predicted theoretical release profile Coating of drug loaded pellets with polymer solution Drug
coated pellets 277.5 g were charged in to conventional coating pan with diameter 375 mm.Different coating loads containing 10% coating solution was sprayed by solution layering technique with an intermittent spraying and drying time of 15-20 min in a coating pan until target weight was achieved.After coating, the pellets were further cured at 40 °C at 75% RH for 24 h.The coating parameters used for coating the drug-loaded pellets were optimized with pre trials.The final composition of drug-loaded pellets coated with different % weight gain is shown in table 4.