Design Formulation and Evaluation of Reservoir Type Controlled Released Moxifloxacin Hydrochloride Ocular Insert

Ramesh B. Parmar¹*, Dr. H. M. Tank²

¹S. J. Thakkar Pharmacy College, Opp NRI bungalow, Avadh Club Road, Munjka, Kalawad Road, Rajkot.

²Matushree V B Manvar Pharmacy College, Dumiyani, Upleta, Rajkot.

*Corresponding Author E-mail: rbparmar82@yahoo.co.in

ABSTRACT

The present studies were mainly focus to developed ocular controlled release formulation of Moxifloxacin Hydrochloride. Reservoir type of ocular insert was developed by solvent casting method. Total nine formulations was developed using different ratio of Eudragit RS 100 and Eudragit RL100 in combination as a rate controlling membrane and reservoir was prepared by using sodium CMC. All the prepared formulation were subjected for evaluation of physicochemical parameter like thickness, weight variation, percentage moisture absorption, percentage moisture loss, surface pH, sterility, drug content and anti-microbial activity. Evaluated results were shown that all the prepared formulation was suitable for patient compliance. In-vitro release study was carried out by using commercial semi-permeable membrane with the help of modified standard cylindrical tube method and best formulation F7 found 98.21 % at the end of 24 hrs. Formulated ocular inserts also passed the test for sterility. The above in vitro release studies revealed that the best ocular inserts formulation followed near to zero-order release kinetics. Higuchi’s plot and Peppa’s plot revealed that the mechanism of drug release involved in all the formulations was super case II transport diffusion. The antimicrobial study was shown that formulation was able to inhibit the microbial growth for extended period of time. The controlled release ocular insert was more suitable as compared to conventional dosage form.

KEYWORDS: Reservoir drug delivery system, ocular insert, Moxifloxacin Hydrochloride, Eudragit RS100, Eudragit RL 100

INTRODUCTION:

The eye is a one of the most, after oral route, interesting organ for local drug delivery of the medicaments. The eye is generally used for local therapy against systemic therapy in order to avoid the risk of eye damage from high blood concentrations of the drug.¹The physiological constraints imposed by the protective mechanisms of the eye lead to low absorption of drugs and a short duration of the therapeutic effect on ocular drug delivery. Upon instillation of the eye drops only 1–10% of the drug is bioavailable while the rest is drained out of the eye through lacrimal secretions.²To overcome this problem various approaches have been reported, such as ointments, inserts and aqueous gels, to increase the ocular residence time of topically applied medication. Controlled drug delivery to the eye offer several advantages over conventional therapies like drug solutions or suspensions as eye drops.

Ophthalmic inserts offer many advantages over conventional dosage forms, like increased ocular residence, possibility of releasing drugs at a slow and constant rate, accurate dosing, and exclusion of preservatives, increased shelf life and reduced systemic absorption. Newer ocular drug delivery systems are being explored to develop extended duration and controlled release strategy. Some of the newer, sensitive and successful ocular delivery systems like inserts, biodegradable polymeric systems, and collagen shields are being developed in order to attain better ocular bioavailability and sustained action of ocular drugs.^3,4

Moxifloxacin HCL is (4aS - cis) - 1 - Cyclopropyl - 6 - fluoro - 1,4 - dihydro - 8 - methoxy - 7 - (octahydro - 6H – pyrrolol [3,4 - b]pyridin - 6 - yl) - 4 - oxo - 3 - quinolinecarboxylic acid monohydrochloride. Moxifloxacin hydrochloride (HCl) is a fourth-generation fluoroquinolone with a new 8-methoxy derivate of fluoroquinolones with enhanced activity in vitro against gram positive bacteria and maintenance of activity against gram negative bacteria.³² It is an anti-infective agent useful in the treatment of eye infection such as bacterial conjunctivitis, keratitis and keratoconjunctivitis. It is presently available as eye drops (0.5%). It is administered at dosing interval of 1 drop in the affected eye 3 times a day for 7 days.^5,6

In the present study, it was aimed to prepare ocular films containing Moxifloxacin Hydrochloride to overcome limitations associated with convectional dosage, an attempt has been made to formulate ocular inserts that may not only improve the efficiency of the therapy but also patient compliance.

MATERIAL AND METHODS:

Material

Moxifloxacin Hydrochloride was obtained from Torrent Pharm Pvt. Ltd. Ahmadabad. Eudragit RS 100 and Eudragit RL 100 were gifted by Evonik Degussa India Private Limited, Mumbai. Sodium CMC, Dibutyl phthalate, glycerin and other reagent was commercial purchased from SD Fine Chem. and Merck Pvt. Ltd.

Methodology

Preparation of ocular inserts:⁷

The preparation of ocular inserts involved three steps: (i) preparation of the drug-containing reservoir film of Sodium CMC, (ii) preparation of rate controlling films of Eudragit, (iii) placing rate controlling films around the drug reservoir and sealing them to obtain ocular inserts.

For preparation of the drug containing reservoir film, accurately weighed quantity of sodium CMC was soaked in the 1/3^rd volume of the distilled water for 24 hours. Weighed Calculated amount of Moxifloxacin Hydrochloride was dispersed in the polymeric solution, after the complete dispersion of the drug; glycerin (Plasticizer: 30% dry weight of polymer) was added and stirred to form a uniform dispersion. The dispersion was casted onto mercury substrate kept in the hot air oven at 40°C for 24 hours. The patches thus formed were cut into diameter of 6mm. Each ocular insert containing 2 mg of Moxifloxacin Hydrochloride. The composition of the polymeric patches containing Moxifloxacin Hydrochloride is given in (Table 1).

For preparation of the rate controlling film, the Eudragit RS 100 and Eudragit RL 100 rate controlling membrane was prepared by solvent casting technique. Eudragit RS 100 and Eudragit RL 100 in different ratio as per (as per Table 1) was dissolved in 1/3^rd quantity of acetone and the plasticizer (15% dry weight of polymer) dibutyl phthalate was dissolved in remaining acetone, then both the solutions were mixed together thoroughly to get the uniform dispersion. This solution was poured on mercury substrate and dried at room temperature for 24 hours. After drying 8 mm diameter were cut using stainless steel borer.

The medicated reservoir film cut with the help of a stainless steel die. These ocular inserts were placed on a rate-controlling membrane and another rate controlling membrane was kept over it. The two rate-controlling membranes containing the reservoir film between them were sealed with the help of acetone. This procedure resulted in sealing the two rate-controlling membranes containing the medicated reservoir film between them. The ocular inserts were stored in an airtight container under ambient conditions for further use.

Evaluation of Ocular Inserts

Thickness⁸

The thickness of the ocular insert was measured using micrometer screw gauge. The thickness was measured at five different spots of the patch and average was taken.

Weight variation⁸

From every batch, three ocular inserts were taken and their individual weights were determined by using electronic balance. The mean weight of insert was noted

Moisture absorption⁹

The percentage moisture uptake test was carried out to check physical stability or integrity of ocular inserts. Ocular inserts were weighed and placed in a desecrator containing 100ml. of saturated solution of Aluminum Chloride and 79.5% humidity was maintained. After three days the ocular insert were taken out and reweighed, the percentage moisture uptake was calculated by using formula.

% Moisture absorption =

(1)

Table 1: Different Formulation of Moxifloxacin Hydrochloride ocular insert

Formulation	Drug Reservoir		Rate Controlling Membrane
	Film Former (% w/v)	Plasticizer (% w/w)	Film Former		Plasticizer (% w/w)
	Film Former (% w/v)	Plasticizer (% w/w)	Eudragit RS 100 (%w/v)	Eudragit RL 100 (%w/v)	Plasticizer (% w/w)
F1	2	30	1	1.5	15
F2	2	30	1.5	1.5	15
F3	2	30	2	1.5	15
F4	2	30	1	2	15
F5	2	30	1.5	2	15
F6	2	30	2	2	15
F7	2	30	1	2.5	15
F8	2	30	1.5	2.5	15
F9	2	30	2	2.5	15

Moisture Loss ⁹

The percentage moisture loss was carried out to check integrity of the film at dry condition. Ocular inserts were weighed and kept in a desecrator containing anhydrous calcium chloride. After 3 days, the ocular insert were taken out and reweighed, the percentage moisture loss was calculated using the formula.

%Moisture loss =

(2)

Folding Endurance^10,11

The flexibility of ocular insert can be measured quantitatively in terms of what is known as folding endurance. Folding endurance of the patches was determined by repeatedly folding a small strip of the patch (approximately 2x2 cm) at the same place till it broke. The number of times patch could be folded at the same place, without breaking gives the value of folding endurance.

Surface pH¹²

The inserts were allowed to swell in closed petridish at room temperature for 30 minutes in 0.1 ml of double distilled water. The swollen device was removed and placed under digital pH meter to determine the surface pH.

Drug Content Uniformity¹³

To check the drug content uniformity, three inserts were taken out from each film and drug content determined using the procedure of IP for Moxifloxacin Hydrochloride. Amount of Moxifloxacin Hydrochloride in one insert is given by:

C = ₍₃₎

Where, As is the absorbance of sample solution, Cr is the concentration of Moxifloxacin Hydrochloride in standard solution, and Ar is the absorbance of standard solution of Moxifloxacin Hydrochloride. The same procedure adopted for all the batches and drug content was noted.

Sterility testing¹⁴

Ultra-Violet radiation was used to sterilize the ocular inserts and sterility testing was carried out under aseptic conditions. It was found visually that the Alternate thioglycolate, Soyabean casein digest media; Fluid thioglygolate media containing sterilized ocular inserts were free from turbidity. This confirmed the absence of aerobic organism, anaerobic organism and fungi.

Microbiological studies¹⁵

The optimized ocular insert was evaluated microbiologically for controlled drug release for 1 day. The test microorganisms E. coli and S. aureus were used. A layer of seeded agar (10 mL) was allowed to solidify in the Petri plate. An ocular insert was removed from the pack and carefully placed over the agar layer and a second layer of seeded agar (10 mL) was applied to cover the insert. After solidification, the Petri plate was incubated in inverted position for 24 h at 37±0.5 ºC. After incubation, the length, width and area of zone of inhibition were measured around the ocular insert. Normal saline served as a negative control.

In-vitro diffusion studies^16,17

The in-vitro diffusion of drug from the different ophthalmic insert was studied using the classical standard cylindrical tube method according to literature. In brief, a simple modification of a glass tube of 12 mm internal diameter and 75 mm height. The diffusion cell membrane was tied to one end of open cylinder, which acted as a donor compartment. An ocular insert was placed inside donor compartment. The diffusion cell membrane (commercial semi-permeable membrane) acted as corneal epithelium. The entire surface of the membrane was in contact with the receptor compartment containing 50 ml of simulated tear fluid (STF) in 100 ml of beaker. The content of receptor compartment was stirred continuously using a magnetic stirrer and temperature was maintained at 370±0.5⁰C. At specific intervals of time, 3 ml of the sample solution was withdrawn from the receptor compartment and replaced with fresh simulated tear fluid (STF) solutions. The sample was analyzed for the drug content using UV-VIS spectrophotometer at 288 nm after appropriate dilutions against reference using simulated tear fluid (STF) as blank. Simulated tear fluid (STF: sodium chloride: 0.670 g, sodium bicarbonate: 0.200 g, calcium chloride.2H2O: 0.008 g, and Purified water q. S. 100 g)

Kinetic analysis¹⁸

To understand the release profile and release mechanism of in-virto release of drug zero order kinetics equation and Korsemeyer's equation was used. When a graph of the cumulative percentage of the drug released from the matrix against time is plotted, zero order release is linear in such a plot, indicating that the release rate is independent of concentration. The rate of release of the drug can be described mathematically as follows:

Rate of release = (dC_s/t) = k (4)

Where C_s = concentration of the drug present in the matrix, k = rate constant and t = time. Since Cs is a constant, and x = amount of drug released described as

dx/dt = k integration of the equation yields (5)

x = k t + constant (6)

A plot of x versus t results in a straight line with the slope = k. The value of k indicates the amount of the drug released per unit of time and the intercept of the line at time zero is equal to the constant in the equation. The curves plotted may have different slopes, and hence it becomes difficult to exactly pinpoint which curve follows perfect zero order release kinetics. Therefore, to confirm the kinetics of drug release, in vitro data were also analyzed using Korsemeyer’s equation.

Korsemeyer et al. used a simple empirical equation to describe general solute release behavior from controlled release polymer matrices:

m_t/m_∞ = k ×tⁿ(7)

Where m_t/m_∞ = fraction of drug released, k = kinetic constant, t = release time and n = the diffusional exponent for drug release. The slope of the linear curve gives the ‘n’ value. Peppas stated that the above equation could adequately describe the release of solutes from slabs, spheres, cylinders and discs, regardless of the release mechanism. The value of ‘n’ gives an indication of the release mechanism. When n = 1, the release rate is independent of time (zero order) (case II transport); n = 0.5 for Fickian diffusion; and when 0.5 < n < 1, diffusion and

Non-Fickian transports are implicated. Lastly, when n > 1.0 super case II transport is apparent. ‘n’ is the slope value of log m_t/m_∞ versus log time curve.

RESULTS AND DISCUSSION:

Preparation of ocular insert

The reservoir type of the ocular insert consisted of three layers of films, the inner reservoir film containing the drug and two-rate controlling films surrounding the reservoir. The ocular inserts are composed of a central reservoir of drug enclosed in specially designed semi permeable or micro porous membranes that allow the drug to diffuse from the reservoir at a precisely determined rate. The reservoir membrane was prepared by 2 % sodium CMC polymer and glycerin was subjected as a plasticizer in concentration of 30 % w/w. To prepare rate controlling films, combinations of Eudragit RS 100 and RL 100 were assayed in different ratios and dibutyl phthalate was chosen as plasticizer. Flexible, uniform and transparent films were obtained containing 15% (w/w) of plasticizer per dry mass of polymer.

Physical parameter

Thickness:

The prepared ocular inserts were evaluated for the thickness using micrometer screw gauge. The average of three readings was taken. It was found to be in the range of 0.212 ± 0.05 mm to 0.316 ±0.01 mm (Table 2). This indicated that as the concentration of the polymers increased, there was increase in the thickness of the ocular inserts.

Uniformity of weights:

The weights of ocular inserts of Moxifloxacin Hydrochloride were found in between 0.211± 0.05 to 0.351±0.01 (Table 2). The mean weight and standard deviation were calculated. The low standard deviation that indicates that uniformity of the weights of the films means good distribution of the drug, polymer and plasticizer.

Percentage moisture absorption:

The percentage moisture absorption were carried out all the formulation and it was found in the ranged of 4.051±0.22 to 7.023±0.23 (Table 2). The moisture absorption was continuously increased when concentration of Eudragite RL100 was increased. This is may be permeability effect of Eudragite RL 100. Higher the concentration higher the moisture absorption.

Percentage moisture loss:

The percentage moisture loss were carried out all the formulation and it was found in the ranged of 4.230±0.21to 7.258±0.46 (Table 2). The moisture loss was continuously increased when concentration of Eudragite RL100 was increased. This is may be the permeability affect of Eudragite RL 100, higher the concentration of polymer higher the moisture loss.

Folding endurance:

Folding endurance of the patches was determined by repeatedly folding a small strip of the patch at the same place till it broke. Range of folding endurance was between 198±1.023 to 221±2.053 (Table 2). The values of folding endurance of the film were found to be optimum and therefore the film exhibited good physical and mechanical properties.

Surface pH:

The prepared ocular insert was subjected for measurement of pH and it was found in range of 6.65 to 7.20 (Table 2). The pH range of all the formulation was found near to tear fluid pH so patient compliance of ocular insert is good.

Drug content:

The drug content of the formulations was determined according to procedure described in methods. The drug content in all formulations was found to contain 1.95±0.01 to 2.01±0.03 (Table 2).

Table 2: Physicochemical parameters of ocular insert

Formulation code	Thickness (mm)	Weight variation (g)	% Moisture Absorption	% Moisture Loss	Surface pH	Drug Content (mg)	Folding Endurance
F1	0.212±0.05	0.211±0.07	4.051±0.22	4.230±0.21	6.98	1.95±0.01	198±1.023
F2	0.235±0.01	0.215±0.09	5.998±0.05	5.021±0.12	6.65	1.96±0.06	206±2.035
F3	0.242±0.03	0.221±0.02	6.582±0.35	5.231±0.09	6.89	2.01±0.03	215±1.520
F4	0.275±0.01	0.286±0.06	5.256±0.21	4.250±0.11	7.01	1.99±0.01	253±3.021
F5	0.281±0.03	0.291±0.04	5.321±0.53	5.062±0.23	6.85	1.98±0.03	231±1.085
F6	0.282±0.02	0.298±0.05	6.036±0.21	6.231±0.02	6.95	1.99±0.01	211±0.890
F7	0.301±0.06	0.315±0.02	6.368±0.22	6.256±0.25	7.20	2.00±0.01	221±2.053
F8	0.298±0.04	0.326±0.01	6.556±0.05	6.236±0.52	7.09	1.96±0.03	212±1.053
F9	0.316±0.01	0.351±0.01	7.023±0.23	7.258±0.46	7.13	1.99±0.02	216±3.240

Table 3: Kinetic release profile of different Moxifloxacin Hydrochloride ocular inserts

Formulations Code	Zero order plot		Higuchi’s plot		Korsemeyer's and Peppa’s plot
Formulations Code	Slope (K₀ )	Correlation ( r2 )	Slope ( K_H )	Correlation ( r2 )	Slope ( n )	Correlation (r2 )
F1	3.7440	0.9794	22.609	0.9073	1.175	0.9762
F2	3.7401	0.9833	22.66	0.9172	1.793	0.9648
F3	3.681	0.9854	22.384	0.9258	1.717	0.9695
F4	3.8679	0.9958	23.809	0.9587	1.335	0.9953
F5	3.7324	0.9966	22.854	0.9495	1.405	0.9961
F6	3.5162	0.9939	21.555	0.9491	1.409	0.9811
F7	4.1776	0.9985	25.807	0.9685	1.191	0.9934
F8	4.0148	0.9930	24.869	0.9682	1.170	0.9910
F9	4.1286	0.9913	25.446	0.9636	1.208	0.9920

CONCLUSION:

From above results it can be concluded that Moxifloxacin HCl can be delivered in controlled manners for extended period of time in the form of ocular inserts. Release pattern of drug from these inserts can be altered by using different formulation variables. The said promising formulation (F7) would be able to offer benefits such as increase residence time, prolonged drug release, reduction in frequency of administration and thereby definitely prove to improve the patient compliance. Further work may be carried out to establish the therapeutic utility of this system by pharmacokinetic and pharmacodynamic studies in human beings.

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Received on 29.12.2012 Accepted on 27.01.2013

Asian J. Res. Pharm. Sci. 3(1): Jan.-Mar. 2013; Page 19-24