INTRODUCTION:

Multiparticulate drug delivery systems like pellets, granules, micro particles, minitablets etc., prove to be promising and highly flexible systems with ease of formulating with different drug release kinetics. These Multiparticulate dosage forms are essential where drug-excipients or drug-drug physicochemical interactions are possible in a single-unit formulation.

In present times, Pelletization technologies are gaining much attention as they represent an efficient pathway for manufacture of oral drug delivery systems^1-2.

The primary aim of using delayed release products is to protect the drug from gastric fluids, to reduce gastric distress caused by drugs particularly irritating to the stomach or to facilitate gastrointestinal transit for drugs that are better absorbed from intestine. Enteric polymers are becoming very popular due to their property of intact in the stomach, but will dissolve and release of the contents once it reaches the small intestine, their prime intension is to delay the release of drugs, which are inactivated by the stomach contents or may cause bleeding or nausea by the irritation of gastric mucosa. Omeprazole is a proton pump inhibitor used for short-term treatment of acid peptic disease, gastro esophageal reflux, gastric ulcer, duodenal ulcer, and Zollinger-Ellison syndrome and for maintenance treatment of Gastro Esophageal Reflux Disease (GERD). It is highly acid labile and presents many formulation challenges and to protect it from acidic environment of the stomach an enteric coated pellets formulation was tried in the present study.

ADVANTAGES^3-4:

· Pellets offer high degree of flexibility in the design and development of oral dosage form like suspension, sachet, tablet and capsule.

· Pellets provide improved flow properties that aid in formulation development like ease of capsule filling without significant difficulties (resulting in uniform and reproducible fill weight of capsules).

· Pellets are less susceptible to dose dumping.

· They can disperse freely in GI tract, maximize drug absorption, and minimize local irritation of the mucosa by certain irritant drugs.

· Pellets offer reduced variation in gastric emptying rate and intestinal transit time.

· The easiest shape to coat is the sphere due to the absence of edges. It is also the most economical because no extra coating material is required to fill irregularities as in case of granules.

· Hardness and friability depend on the internal cohesive forces and surface characteristics. Pelletization increases the hardness and reduces the friability; consequently reduce the amount of fines generated during handling or transportation.

DISADVANTAGES OF PELLETS:

· The size of pellets varies from formulation to formulation but usually lies between 1 to 2mm.

· Low drug loading, proportionally higher need for excipient.

· Lack of manufacturing reproducibility and efficacy.

· Large number of process variables.

· Multiple formulation steps.

· Higher cost of production.

· Need of advanced technology.

PELLETIZATION METHODS^5-6:

Pelletized dosage forms can be prepared by a number of techniques, including

· Drug layering on nonpareil sugar or microcrystalline cellulose beads

· Extrusion spheronization technique

· Spray drying

· Spray congealing

· Cryopelletization

· Compression

· Melt extrusion technology

· Freeze Pelletization

· Rotary processor technique

· Use of rotary shaker pelletizer

Layering was carried out in Fluid bed systems. These are of three types shown in following diagram^7.

1. Granulator, Top-spray process is preferred when a taste masking coating is being applied and granulation of drug(s) combined with excipient(s). Additionally it is suitable for the application of hot melt coating. The long expansion chamber allows the particles to decelerate in a high velocity fluidized air stream for much longer period as well as minimized agglomeration. The nozzle positioned in such a way to achieve uniform spray without spray- drying.

2. Wurster, Bottom spray process is preferred for the application of modified-release coating to a wide variety of multi particulates; also suitable for drug layering when the drug dose is in low to medium range. Bottom spray coater consists of (a) product container with bottom fitted perforated plate for fluidization of particles (b) Wurster positioned at the bottom in such a way to assert flower shaped circulation of particles (c) spray nozzle.

3. Rotor, Tangential spray process is suitable for the application of modified-release film coating to a wide range of multiparticulate products. It is ideal for drug layering when the dose is medium to high. It is also useful as a spheronizing process for producing spheres.

MATERIALS AND METHODS:

Materials Used:

Omeprazole gift sample was provided by Natco Pharma Limited, Hyderabad, India. Non pareil seeds (18/20#) were provided by Time Cap Pharma Ltd., (Natco Pharma Group) Hyderabad, India. All excipients i.e. Sodium lauryl sulphte, Calcium carbonate, eudragitL30D55, HPMCE5, Poly ethylene glycol 6000,Talc and Titanium dioxide were provided by Natco Pharma Limited, Hyderabad, India and others reagents were of analytical grade.

Equipments: Balance (Shimadzu, Mumbai), FBC (Platinum Pharma Mumbai), R & D Coater (VJ Instruments, Mumbai), Ultrasonic bath Sonicator (Pci analytics), Friabilator (Roche friabilator, Mumbai), dissolution test apparatus (DT 03071009, lab India- Mumbai, 2000); and UV-visible spectrophotometer (SL159, Elico Ltd., Hyderabad), Fourier transform infrared (Bruker, Germany) were used in research work.

Methods Used:

Drug Loading^8-9:

Specified quantity of non-pareil seeds was accurately weighed and dispensed. Sufficient amount of purified water is taken in a beaker and kept for stirring under a mechanical stirrer. Specified quantities of PVP K 30, disodium hydrogen phosphate, calcium carbonate and Sodium Lauryl sulphate were added slowly to form a uniform suspension. Specified quantity of Omeprazole is added and stirring is continued for 30 min. Non pareil seeds were coated with the prepared drug suspension using pan coater. Dried pellets were collected and coating efficiency was calculated.

Preparation of Barrier coated/Sub coated Pellets:

Purified water is taken in a beaker and kept for stirring under a mechanical stirrer. Specified quantities of HPMC E 5, Titanium dioxide were added slowly to form a uniform suspension. Drug loaded pellets were coated with the above suspension using Fluidized Bed Coater (FBC).

Preparation of Enteric Coated Pellets:

Purified water were taken in a beaker and. Specified quantities of enteric coating polymer, plasticizers (Eudragit L 30 D55, PEG 6000 or Tween80), and kept for stirring under a mechanical stirrer ,Titanium dioxide and Talc (previously passed through 20#) were added slowly to form a uniform suspension. Stirring was continued for 30 min. Barrier coated pellets were coated with the above suspension using Fluidized Bed Coater (FBC). Dried pellets were collected and coating efficiency was calculated.

Evaluation of pellets ^10-12: the following micromeritic properties of Omeprazole enteric coated pellets were studied.

Angle of Repose:

Angle of repose is used to determine the flow properties of powders, pellets or granules. The Method to find angle of repose is to pour the powder on a conical heap on a level, flat surface and measure the included angle with the horizontal.

Tan θ = h/r

Where, h = height of the heap,

r = Radius of the heap.

Bulk Density:

Bulk density of the coated pellets was determined by pouring pellets into a graduated cylinder via a large funnel and measuring the volume and weight.

Bulk density = weight of granules

Bulk volume of granules

Tapped Density:

Tapped density was determined by placing a graduated cylinder containing a known mass of granules and mechanical tapper apparatus, which was operated for a fixed number of taps until the powder bed volume has reached a minimum volume. Using the weight of the drug in the cylinder and this minimum volume, the taped density may be computed.

Tapped density = weight of granules

Tapped volume of granules

Carr’s Index:

Carr’s index is measured using the values of bulk density and tapped density. The following equation is used to find the Carr’s index.

CI = (BD-TD) x 100

Where, TD = Tapped density

BD = Bulk density

Moisture content:

One gram of pellets were weighed and kept in an oven at 70ºC. Its weight was noted as initial weight (W₁). They were removed from the oven after regular time intervals of 15min and weighed. Loss in weight of pellets was noted. After attaining constant weight, it was noted as final weight (W₂) and percent moisture content was calculated. It was calculated using below formula;

Moisture content =

FTIR analysis:

FTIR spectra of drug and optimized formulation were obtained. Sample about 5 mg was mixed thoroughly with 100 mg potassium bromide IR powder and compacted under vacuum at a pressure of about 12Psi for 3 minutes. The resultant disc was mounted in holder in IR spectrophotometer and the IR spectrum was recorded from 3500cm-1 to 671 cm-1 in a scan time of 12 minutes. The resultant spectra were compared for any spectral changes.

Assay:

Standard preparation:

Weigh accurately about 75 mg of Omeprazole working standard into 100 ml of volumetric flask add 50 ml of Methanol sonicated and shake well and diluted to volume with Methanol, mixed well. Pipetted out 2 ml of this solution in to 100 ml volumetric flask diluted to volume with DM water and mix well.

Sample Preparation:

Weigh accurately about 75 mg drug equivalent pellets in a 100 ml volumetric flask; add 50 ml of Methanol, sonicated for 10 minutes. Cool and dilute to volume with Methanol. Filter the solution through what man filter paper. Then take 2 ml of filtrate into 100 ml volumetric flask. And dilute to volume with DM water.

Procedure:

Scan the solution of both standard and sample preparation against Blank preparation between 200nm and 400 nm measure the absorbance for both standard and sample at 301 nm.

Calculation: A= AT × WS× 2 × 100 × 100 ×p

As 100 100 Wt 2

Where

AT =Absorbance of the sample preparation.

P = Purity of the standard

AS = Absorbance of the standard preparation.

WS = Weight of the standard taken in mg

WT = Weight of the sample taken in mg

In-vitro Dissolution:

Apparatus	:	USP APPARATUS II
Medium	:	0.1N HCl up to 1st two hours, pH 1.2Phosphate buffer (pH 6.8 for) remaining hours
Sampling interval	:	5 minutes.
Rpm	:	100
Temperature	:	37°C ±0.5°C

Procedure:

Weight accurate amount of Omeprazole pellets individually in the dissolution flasks, containing 900ml of 0.1N HCl. Previously adjust the temperatureto37oC±0.5^oC. Collect the samples for first 2hrs and later replace the medium with phosphate buffer 6.8 and collect the samples for remaining 45 min from a zone midway between the surface of the medium and the top of the rotating blade and not less than 1cm from the vessel wall and filter through 0.45μ membrane filter by discarding the first 5ml.The absorbance is measured at 301nm by using UV-spectrophotometer.

RESULTS AND DISCUSSION:

Pre formulation studies:

Micromeritic properties Omeprazole:

Omeprazole was evaluated for flow properties such as angle of repose, Carr’s index and Hausner’s ratio. The results of angle of repose, Carr’s index and Hausner’s ratio of the Omeprazole were 33, 10.51 and 1.53 respectively. From the above results it reveals that, Omeprazole exhibited poor flow properties.

Micromeritic properties drug and polymer coated pellets:

The results of Carr’s index of the Omeprazole enteric coated formulations F_1-F7were found to be 7.3, 5.4, 8.1, 7.7, 8.2, 8.1 and 8.7 respectively. The results of Hausner’s ratio of the Omeprazole pellets formulations F_1-F7 were found to be 0.93, 0.94, 0.91, 0.92, 0.91, 0.91 and 0.91 respectively. From the above results, it was observed that all the formulations exhibited good flow properties (tableno-3).

Physical properties of pellets:

Physical properties of pellets like friability, moisture content and drug content were found to comply with the pharmacopoeial standards and results were shown in the table no-4.The friability of all the formulations was found to be less than 1% and drug content of the formulations was in between 95-99% that meets the official specifications (90-110%)

In-vitro drug release studies:

The in-vitro release of Omeprazole enteric coated pellets were studied for first two hours in P^H 1.2 and for subsequent 45 min in phosphate buffer of P^H6.8.It is reasonable to conclude that the release profile of Omeprazole enteric coated pellets showed two distinct phases. An initial burst release phase occurs in the first two hours, followed by gradual release phase.

The formulations (F1, F2, F3, F4, F5, F6, and F7) were subjected to in-vitro dissolution studies were carried out up to 2hours 45 min respectively.

The results of in-vitro drug release studies for F₁, F₂, F₃,F4,F5,F6 and F7 were reported in table 5.The comparative in-vitro release profile was depicted in Figures 1,2.The percentage of drug released for the formulations F₁-F7 were found to be 70.7%, 73.0%, 79.9%, 84.5%, 94.4%, 98.2.%, 96.6%, at the end of 45min respectively. The drug release mechanisms were analyzed by fitting the in-vitro release data into various models, First order, Zero order as shown in table 5.6, 5.8. The drug release from the formulations F_1-F7 formulations followed first order kinetics. The rate constants (K values) were found to be 10.6, 11.8, 12.2, 20.6, 27.0, 28.8, 27.2 mg/min. The release exponents ‘n’ for formulations F₁-F7 were found to be 0.47, 0.45, 0.42, 0.36, 0.33, 0.32, 0.33, and indicating the release was governed by Fickian anomalous transport. From the in –vitro dissolution data it was found that formulations F4,F5,F6 and F7 releases more than 80% of drug release at the end of 45min . The study indicating that the surfactant concentrations were found to be 0.25%, 0.5%, 0.75%, 1%.

The drug release studies, formulation F6 (0.75% of SLS) showed desired in-vitro drug release.

The drug release rate of Omeprazole enteric coated pellets were found to be affected by the concentration of sodium lauryl sulphate used in the formulation. As the concentration of surfactant was increased, the drug release was found to be increased.

Statistical Evaluation:

The relevance of difference in the in-vitro diffusion rate profile was evaluated statistically. Statistical analysis by using One-way analysis of variance (P<0.05) proves that pellets prepared with synthetic polymers and various concentrations of sodium lauryl sulphate indicates that the dissolution rate constants were significantly differ with each other (Figure-3)

Drug –excipient compatibility studies:

The spectrum of selected formulation, it was observed that the intensive absorption bands were noted around the same wave numbers.

Table: 1. Formulations of Omeprazole pellets with synthetic polymers and different concentrations of surfactants:

S.No.	Ingredients	F1	F2	F3	F4	F5	F6	F7
Drug blend formula(gms):
1	Omeprazole	42.75	42.5	86	86	86	86	86
2	DSHP	6.45	6.45	12.86	12.86	12.86	12.86	12.86
3	CaCo₃	17.25	17.25	34.26	36.99	35.42	33.95	32.32
4	SLS	2.25	2.25	4.26	1.53	3.1	4.57	6.2
5	Sugar powder	128.25	128.25	257.14	257.14	257.14	257.14	257.14
6	Maize starch	167.25	107.25	214.29	214.29	214.29	214.29	214.29
Drug loading:
7	PVPK₃₀	0.45	0.45	0.86	0.86	0.86	0.86	0.86
8	SLS	0.086	0.086	0.171	0.171	0.171	0.171	0.171
9	PG Sugar	21.45	21.45	42.86	42.86	42.86	42.86	42.86
10	Water	85.73	86	171.43	171.43	171.43	171.43	171.43
Barrier Coating:
11	HPME E₅	22.15	36.63	72.54	72.54	72.54	72.54	72.54
12	Tio₂	2.45	2.5	4.03	4.03	4.03	4.03	4.03
13	Water	376.55	622.70	1233.18	1233.18	1233.18	1233.18	1233.18
Enteric coating:
14	EudragitL₃₀D₅₅	189.66	168.21	664.93	664.93	664.93	664.93	664.93
15	Talc	9.37	8.41	33.25	33.25	33.25	33.25	33.25
16	Tio₂	3.95	3.36	13.30	13.30	13.30	13.30	13.30
17	PEG 6000	6.75	6.10	23.94	23.94	23.94	23.94	23.94
18	Tween 80	0.94	0.84	3.32	3.32	3.32	3.32	3.32
19	NaoH	0.393	0.34	3.84	3.84	3.84	3.84	3.84

Table-2 Process variables for Omeprazole enteric coated formulations:

Parameters Setvalue
DRUG LOADING:
Process variables	F1	F2	F3	F4	F5	F6	F7
Peristaltic pump RPM	25-28	27-29	27-31	27-31	27-31	27-31	27-31
Atomization air pressure	1.69Kgcm^-2	1.74Kgcm^-2	1.6-3.2Kgcm^-2	1.6-3.2Kgcm^-2	1.6-3.2Kgcm^-2	1.6-3.2Kgcm^-2	1.6-3.2Kgcm^-2
Pan RPM	8-10	9-13	9-15	9-15	9-15	9-15	9-15
Blower temperature	50-65^oC	55-70^oC	70-75^oC	70-75^oC	70-75^oC	70-75^oC	70-75^oC
Exhaust temperature	40-50^oC	40-55^oC	40-60^oC	40-60^oC	40-60^oC	40-60^oC	40-60^oC
BARRIER COATING:
Pump RPM	2-4	2-5	2-4	2-4	2-4	2-4	2-4
Inlet temperature	45-50^oC	40-50^oC	52-58^oC	52-58^oC	52-58^oC	52-58^oC	52-58^oC
Exhaust temperature	41-46^oC	41-45^oC	48-51^oC	48-51^oC	48-51^oC	48-51^oC	48-51^oC
Product temperature	45-50^oC	45-50^oC	50-55^oC	50-55^oC	50-55^oC	50-55^oC	50-55^oC
Atomization air pressure	1.72Kgcm^-2	1.72Kgcm^-2	1.8Kgcm^-2	1.8Kgcm^-2	1.8Kgcm^-2	1.8Kgcm^-2	1.8Kgcm^-2
%damper opening	6.5	6.3	7	7	7	7	7
Column height	0.8cm	0.8cm	0.8cm	0.8cm	0.8cm	0.8cm	0.8cm
ENTERIC COATING:
Pump RPM	2-4	2-5	2-4	2-4	2-4	2-4	2-4
Inlet temperature	45-50^oC	40-50^oC	52-58^oC	52-58^oC	52-58^oC	52-58^oC	52-58^oC
Exhaust temperature	41-46^oC	41-45^oC	48-51^oC	48-51^oC	48-51^oC	48-51^oC	48-51^oC
Product temperature	45-50^oC	45-50^oC	50-55^oC	50-55^oC	50-55^oC	50-55^oC	50-55^oC
Atomization air pressure	1.72Kgcm^-2	1.72Kgcm^-2	1.8Kgcm^-2	1.8Kgcm^-2	1.8Kgcm^-2	1.8Kgcm^-2	1.8Kgcm^-2
%damper opening	6.5	6.3	7	7	7	7	7
Column height	0.8cm	0.8cm	0.8cm	0.8cm	0.8cm	0.8cm	0.8cm

Table -3: Micromeritic properties of Omeprazole enteric coated formulations

S.NO:	Formulations	Bulk density(g/ml)	Tapped density	Carr, s index (%)	Hausner ^,s ratio
1	F1	0.952	0.887	7.3	0.931
2	F2	0.947	0.895	5.49	0.945
3	F3	0.938	0.862	8.10	0.918
4	F4	0.925	0.853	7.78	0.922
5	F5	0.917	0.841	8.28	0.917
6	F6	0.906	0.832	8.16	0.918
7	F7	0.901	0.822	8.76	0.912

Table -4: Physical characteristics of Omeprazole with marketed formulation

S.NO:	Formulations	Friability	Moisture content	Drug content
1	F1	0.76	1.89	95
2	F2	0.80	1.93	95
3	F3	0.91	1.94	96
4	F4	0.69	1.95	96
5	F5	0.95	1.97	98
6	F6	0.89	1.86	99
7	F7	0.92	1.96	96

Table-5: In-vitro release kinetics for Omeprazole enteric coated formulations with synthetic polymer and different concentrations of surfactant:

Formulation	Correlation coefficient		T₅₀ (min)	T₉₀ (min)	Exponential coefficient (n	K(mg/min)
Formulation	Zero order	First order	T₅₀ (min)	T₉₀ (min)	Exponential coefficient (n	K(mg/min)
F1	0.79	0.97	15.6	52.2	0.47	10.6
F2	0.89	0.97	20.9	82.6	0.45	11.8
F3	0.95	0.98	25	82.9	0.42	12.2
F4	0.76	0.97	15.7	52.5	0.36	20.6
F5	0.602	0.965	11.3	37.5	0.333	27.05
F6	0.608	0.964	9.0	30	0.323	28.89
F7	0.621	0.965	10.4	34.6	0.331	27.22