1. INTRODUCTION:

Eye being a most delicate organ, ocular drugs delivery is a challenge for the formulator. Recent trend in ocular research is to formulate a dosage form which not only prolongs the residence of system in eye but also helps to reduce the elimination of the drugs and side effects¹. In the present study, successful efforts were made to develop such dosage forms for Brimonidine Tartrate and Timolol.

1.1 Ophthalmic insert^2-3

Inserts are defined as a thin disks or small cylinders made with appropriate polymeric material and fitting into the lower or upper conjunctival sac. Their long persistence in preocular area can result in greater drugs availability with respect to liquid and semisolid formulation.

1.2 Requisites of controlled ocular delivery systems⁴:

1. To overcome the side effects of pulsed dosing (frequent dosing and high concentration) produced by conventional systems.

2. To provide sustained and controlled drugs delivery.

3. To increase the ocular bioavailability of drugs by increasing corneal contact time. This can be achieved by effective coating or adherence to corneal surface, so that the released drugs effectively reach the anterior chamber.

4. To provide targeting within the ocular globe so as to prevent the loss to other ocular tissues.

5. To circumvent the protective barriers like drainage, lacrimation and diversion of exogenous chemicals into the systemic circulation by the conjunctiva.

6. To provide comfort and compliance to the patient and yet improve the therapeutic performance of the drugs over conventional systems.

7. To provide the better housing of the delivery system in the eye so as the loss to other tissues besides cornea is prevented.

1.3 Ophthalmic inserts^5-6

Ophthalmic inserts are defined as elliptical flexible wafer, multilayered system consisting of drugs as core surrounded by rate controlling membrane and designed to be placed in cul-de-sac between sclera and eyelid.

1.4 Advantages of ophthalmic insets⁷

1. increasing the contact time and thus improve bioavailability.

2. Providing prolonged drugs release and thus a better efficacy.

3. Reduction of systemic side effects and thus reduces adverse effects.

4. Reduction of the number of administration and thus better patient compliance.

5. Administration of an accurate dose in the eye and thus a better therapy.

6. Increased shelf life with respect to aqueous solutions.

7. Exclusion of preservative, thus reducing the risk of sensitivity reactions.

8. A possibility of incorporating various novel chemical technological approaches such as pro-drugss, micro particulates, salts acting as buffers.

2. MATERIAL AND METHOD:

PVP was a gift sample from Ciron Drugs Ltd., Mumbai. Sodium alginate and Poly ethylene oxide was a gift sample from Loba Chemie, Mumbai. EC was a gift sample from Alfa Aesar, USA. PMMA Potassium dihydrogen, orthophosphate, Sodium hydroxide, PEG 400, Dibutyl phthalate, Chloroform, Dichloromethane, Acetone, Span 20,40,60,80, Tween 20, 60, 80, Cholesterol, ATGM, SBCDM was a gift sample from SD Fine Chemicals, Mumbai.

3. Preliminary Screening:

Preliminary study was carried out for screening of various polymers and their concentrations.

Selection of Polymers^8-11

Polymers were selected from among PVP, PEO, HPMC, EC and PMMA based on the type of films formed at different concentrations, the strength of the films formed and appearance of the films. Bearing in mind all these factors, it was concluded that PVP and PEO with PMMA form very good films (Table 1). In order to idealize a film for ocular inserts, even combinations of hydrophilic-hydrophobic polymers at different concentrations were tried. Finally, it was deduced that PMMA and PEO can be a better combination to give a sustained release for a prolonged period and also fulfill the other requirements at various concentration.

Formulation compositions for preliminary screening of polymers for films

Ingredients A1 A2 A3 A4 A5 A6 A7

Brimonidine Tartrate 0.2 % 0.2 % 0.2 % 0.2 % 0.2 % 0.2 % 0.2 %

Timolol 0.5% 0.5% 0.5% 0.5% 0.5% 0.5% 0.5%

PEO 167 --- 167 --- --- 150

PVP --- 240 --- --- 240 --- 150

HPMC --- --- 167 --- --- 167 ---

Ethyl Cellulose 333 360 333 --- --- --- ---

PMMA --- --- --- 333 360 333 ---

PEG 400 --- --- --- --- --- --- 100

Dibutyl Phthalate 150 180 150 150 180 150 ---

Solvent S1 S1 S2 S2 S1 S2

Water

(All values are in mg)

Solvent: S1: Dichloromethane: Acetone (1:1) and S2: Chloroform: DCM (6:4)

This investigation was aimed to use composite polymer in matrix type ocular formulation. For screening the polymers and polymer blend a formulation study was carried out. Above Table 1 shows some of the important formulations screened for actual study. Formulation A1, A2 and A3 were prepared using EC and hydrophilic polymers combination. It was found that good film was not obtained in case of A3 whereas A1 and A2 gave the film but film obtained was not good in appearance and contents were not distributed uniformly. Formulation A4 to A6 were prepared using PMMA and hydrophilic polymers combination. All the films were good in appearance and uniformity. Considering above result it was decided to prepare the ocular films by using the PEO in combination with PMMA. Formulation A7 prepared with PEO and PVP was better as compared to films of HPMC with PEO and PVP. It was found that alone PMMA was not able to form good film whereas EC alone was able to form good uniform film but it was brittle.

4. FORMULATION OF OCULAR INSERTS¹²

The monolithic films of Drugs with PMMA and PEO were prepared by solvent evaporation technique. Chloroform was used as solvent. The composition of ocular films is shown in Table 2.

Table 2: Formulation compositions for ocular inserts

Inserts	Drugs (%) Brimonidine Tartrate (0.2%): Timolol (0.5%)	Total polymer (% w/v)	PMMA:PEO (Ratio)
F1	0.7%	1	9:1
F2	0.7%	1	8:2
F3	0.7%	1	7:3
F4	0.7%	2	9:1
F5	0.7%	2	8:2
F6	0.7%	2	7:3
F7	0.7%	3	9:1
F8	0.7%	3	8:2
F9	0.7%	3	7:3

All formulations contain dibutyl phthalate as plasticizer 30 % w/w of polymer weight.

The weighed quantities of polymers were dissolved in 13 mL solvent and plasticizers (30% w/w of polymers) were incorporated. To this solution Drugs (0.7%) was added and mixed thoroughly with the help of magnetic stirrer for 10 min at 25 rpm. Polymeric solution was sonicated for 30 sec to remove the air. Polymeric solution was then poured into a Petri dish (6.8cm diameter) placed on a flat even surface. The rate of evaporation was controlled by inverting the funnel over the Petri dish. After drying at room temperature for 24 hr, circular ocular inserts of diameter 6 mm were cut using fabricated mould, sterilized under UV for 10 min and 60 min and packed in aluminum foil and stored in desiccators until further use.

5. EVALUATION STUDY:^13-17

5.1 Weight uniformity:

As weight variation between the formulated films can lead to difference in drugs content and in vitro behavior, evaluation was carried out by weighing 10 films by an electronic balance (least count – 0.1 mg). The average weight and standard deviation were then calculated and reported.

5.2 Thickness:

Thickness of the film is an important factor while considering its drugs release from ocular delivery systems. If thickness varies from one film to another, the drugs release from the film also varies. So it is must to keep the thickness of the film uniform to get reproducible results. In the present study, the thickness of the formulated films was measured using digital micro meter of sensitivity of 0.01mm (mitutoyo, Japan). Average of 3 readings was taken and standard deviation values were calculated.

5.3 Tensile strength and percentage elongation at break:

The tensile strength of ocuserts refers to tension or force required to tear off the insert apart into two pieces. This was determined with an instrument assembled in the laboratory.

Instrument:

A small strip of ocular film measuring 5 cm×1 cm was cut with a sharp blade. One end of the film was fixed by placing in the film holder. Another end of the film was fixed with the help of forceps having triangular ends to keep the strip straight while stretching and a hook was inserted. A thread was tied to the hook, passed over the pulley and a small pan attached to the other end to hold weights. A small pointer was attached to the thread that travels over the graph paper affixed on the base plate.

Procedure:

To determine elongation and tensile strength, the film was pulled by means of a pulley system. Weights were gradually added (5g/min) to the pan to increase the pulling force till the film was broken. Elongation was determined simultaneously by noting the distance traveled by the pointer on the graph paper before the film was broken. The weight necessary to break the film was noted as break force. Percentage elongation at break and tensile strength was calculated using the following formula.

% Elongation at break = IB − Io × 100

Where Io is the original length of the film and IB is the length of the film at break when stress was applied.

Tensile strength = Break force

ab (1+ΔL/L)

Where a, b and L are width, thickness and length of the strip respectively and ΔL is the elongation at break. Break force = weight required to break the film (Kg).

5.4 Folding endurance:

The flexibility of polymeric films can be measured quantitatively in terms of folding endurance. Folding endurance was determined by repeatedly folding a small strip of ocular film (2×2 cm) at the same place till it breaks. The number of times film could be folded at the same place, without breaking gives the value of folding endurance.

5.5 Moisture uptake:

The percentage moisture uptake test was carried out to check the physical stability or integrity of the film. Ocular films were weighed individually and placed in a desiccator containing 100 mL of saturated solution of sodium chloride (~ 75 % humidity). After three days,

films were taken out and reweighed; the percentage moisture uptake was calculated by using following formula.

Percentage moisture uptake = Final weight – Initial Weight/Initial weight × 100

5.6 Percentage moisture content:

The percentage moisture loss test was carried out to check the integrity of the film at dry condition. Ocular films were weighed individually and placed in a desiccator containing anhydrous calcium chloride. After three days, films were taken out and reweighed; the percentage moisture loss was calculated by using following formula.

Percentage moisture content = Initial weight – Final Weight/Initial weight × 100

5.7 Water vapor transmission studies:

The glass vials of 5 mL capacity were washed thoroughly and dried to constant weight in an oven. One gram of fused calcium chloride was taken in vials and the polymer films were fixed over the brim with the help of an adhesive. These pre-weighed vials were stored in humidity chamber at RH 80% with temperature of 25⁰

5.8 Determination of drugs content:

The films were dissolved in 5 mL chloroform. The drugs was extracted from chloroform using phosphate buffer. The volume was adjusted to 100 mL with phosphate buffer pH 7.4 and the solutions were filtered through filter. Chloroform was evaporated at 60⁰C. The drugs content in each formulation was determined spectrophotometrically at 274 nm. Similarly, a blank solution was prepared using dummy film. Average drugs content of three films was determined.

5.9 Surface morphology:

Surface characteristics of polymer blend were studies by scanning electron Microscopy. Films were mounted on an aluminum stub using double-sided adhesive carbon tape and coated with gold palladium using JEOL JFC 1600 auto fine coater for 90 sec. Samples were examined using scanning electron microscope JSM-6380 LV (Jeol Ltd., Tokyo, Japan) at 20 kv accelerating voltage.

6. RESULTS AND DISCUSSION:

Table 3: Physical properties of prepared ocular films

Inserts	Weight of films (mg)*	Thickness (mm)#	Tensile strength#	%Elongation at break# (EB)	Folding endurance#
F1	4.09± 0.069	0.11± 0.016	0.75 ± 0.03	3.26± 0.21	69±2
F2	4.2± 0.046	0.13±0.0063	0.68 ± 0.01	8.13± 0.23	90.3±2.08
F3	4.11± 0.052	0.14±0.007	0.57 ± 0.01	12.63± 0.4	99.3±2.51
F4	6.43± 0.094	0.19 ± 0.015	0.84 ± 0.02	2.95± 0.32	65.3±3.51
F5	6.49± 0.082	0.20± 0.0072	0.72 ± 0.01	7.18± 0.43	81±2.61
F6	6.44± 0.044	0.21± 0.0054	0.65 ± 0.01	12.17± 0.21	94.6±2.08
F7	8.89± 0.057	0.24± 0.0032	1.34 ± 0.05	2.28± 0.32	61.3±2.08
F8	9.09± 0.04	0.24± 0.004	0.92 ± 0.02	7.89± 0.46	73.3±2.52
F9	8.91± 0.052	0.25± 0.0154	0.80 ± 0.02	11.93± 0.54	89.6±3.78

All readings are in the form of Mean±SD, # Average of 3 runs, *Average of 10 determinations.

Table 4: Evaluation of prepared ocular films

Inserts	%Moisture content (%MC ± SD)^a	% Moisture uptake (%MU ± SD)^a	Water-vapour transmission rate (gm/cm²h)^a× 10^-3
F1	2.50 ± 0.07	04.17 ± 0.14	0.85±0.01
F2	2.78 ± 0.05	05.00 ± 0.09	1.21±0.03
F3	4.17 ± 0.12	09.37 ± 0.16	1.84±0.02
F4	2.94 ± 0.04	05.15 ± 0.12	0.96±0.05
F5	4.17 ± 0.10	08.33 ± 0.08	1.36±0.03
F6	5.47 ± 0.15	10.94 ± 0.12	3.06±0.02
F7	3.85 ± 0.09	07.69 ± 0.07	1.14±0.03
F8	4.81 ± 0.08	09.62 ± 0.09	2.21±0.02
F9	6.05 ± 0.17	11.08 ± 0.11	4.20±0.05

Table 5: Drugs content of prepared ocular films

Inserts Drugs content* Drugs content*

(% ± SD) (% ± SD)

F1 0.701±0.0076 102.13±1.51

F2 0.701±0.010 100.2±2.03

F3 0.702±0.006 100.5±1.21

F4 0.706±0.0031 101.27±0.61

F5 0.697±0.0045 99.46±0.90

F6 0.695±0.0021 99.07±0.42

F7 0.699±0.0042 99.87±0.83

F8 0.701±0.0023 100.13±0.46

F9 0.703±0.0042 100.53±0.83

* Average of five readings ± SD

Surface morphology (SEM):

SEM study (Figure 1) revealed that surface of the ocular films are smooth indicating the complete miscibility of PEO with PMMA. The polymers are completely miscible and the blend is amorphous.

Figure 1: Scanning electron microscopy (SEM) images of inserts F7 and F8. Experimental condition: magnification= ×1000, Acc. V 20 kV,

signal SEI, 10 μm

7. CONCLUSION:

Attempt has been made to use blend of polymers in design of sustained ocular delivery system. Study was mainly focused on investigating influence of Hydrophilic (PEO) and hydrophobic (PMMA) polymers and their concentration on ocular delivery using factorial design statistically. Inserts of all batches had desired ocular physicochemical properties. Both polymers amount and their ratio had significant influence on dependent variables studied. The ratio of hydrophilic and hydrophobic polymeric film formers affected the mechanical properties, percentage moisture uptake, WVT rate, rate of drugs release and consequently the permeation of the Drugs. Due to addition of hydrophilic polymer, the surface of inserts was hydrophilic enough to be easily wetted by tear film. The blend of PEO in PMMA matrix was found to be homogenous and blend was amorphous in nature. It was found that drugs permeation was decreased with increasing polymer concentration. It was also concluded that presence of PEO in films favors the drugs release and so permeation whereas PMMA retards drugs release. The results indicate that the polymeric film composed of PMMA and PEO at the ratio of 8:2 and dibutyl phthalate as a plasticizer was suitable for developing an ocular drugs delivery system. Thus the present work showed that incorporation of hydrophilic polymer into hydrophobic matrix system can be successfully done in order to model ocular inserts providing promising controlled release delivery system. The control of IOP, systemic absorption and hence possible side effects using inserts was found to be better than conventional eye drops. Thus, on the basis of In vivo antiglaucoma activity, ocular safety test and stability studies, it can be concluded that this ocular insert can be a promising once-a-day controlled release formulation after due considerations of human in vivo studies.

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Received on 28.07.2016 Modified on 23.08.2016

Res. J. Pharm. Dosage Form. & Tech. 2016; 8(4): 231-236

DOI: 10.5958/0975-4377.2016.00032.X