Formulation and Evaluation of Levofloxacin and Betamethasone Ophthalmic Emulgel.

OBJECTIVE: Drug delivery to ocular tissues is challenging due to rapid removal of instilled drug due to low resident time in ocular tissues. The aim of the study was to formulate an ophthalmic emulgel that delivers two drugs (betamethasone sodium phosphate [BSP] and levofloxacin). The new combination will allow the simultaneous administration and extended release of the two drugs which potentially improve resident time in ocular tissues, patient compliance, and adherence to treatment.
MATERIALS AND METHODS: Formulations containing different gelling agents at different concentrations were prepared to choose the optimum combination regarding physical properties and release. The emulgel formulations F1, F2, F3, and F4 were made using gelling agent 1% and 2% xanthan gum, 1% carbopole 934, and 2% methyl cellulose, respectively. F5 was formulated using 2% methyl cellulose with double the amount of poloxamer 188 as emulsifying agent. All the formulations were examined regarding their physical appearance, pH, viscosity, drug content, and in vitro drug release. The optimum formula was also examined for antibacterial activity.
RESULTS: The results demonstrated that F5 was the optimum formulation having a proper physical characteristics and release profile of both drugs, 96% and 90% for BSP and levofloxacin, respectively, compared to other formulations and commercial eye drops.
CONCLUSION: Simultaneous and extended release of the two drugs was achieved using one formulation of emulgel. The ability to deliver hydrophilic and hydrophobic drug through the same formulation without the need to use two drops will improve patient compliance and hence patient adherence to treatment. Copyright:

INTRODUCTION

Ophthalmic drug delivery is an inspiring and challenging field for formulation scientists. Although the eye seems easily accessible, delivering a drug through ocular tissues is quite challenging due to various anatomical, physiological, and biological barriers. These barriers reduce the efficacy of treatment used.[1234] Topical eye drops are the main dosage form used for the treatment of ocular tissues. In spite of their wide use, their effect is compromised by their short resident time in ocular tissues. Less than 5% of eye drops instilled cross the cornea to reach ocular tissues. Several factors affect their retention time such as blinking reflex, excessive lacrimal secretion, low permeability, rapid dilution, elimination through nasolacrimal drainage, and other elimination mechanisms.[567] Over the years, formulation scientists focus their efforts on developing dosage forms that prolong the retention time of drugs in the eye. Several strategies were investigated and developed such as gels, ointments, minitablets, in situ formulations, drug releasing contact lenses, nanoparticles, liposomes, implants, and inserts.[891011] Gels in particular are interesting as dosage forms. They are polymeric crosslinked networks incorporating large amount of water in their structure (almost 90% of their composition is water). Their unique composition render them highly biocompatible and less irritant to eye tissues compared to other formulations.[121314] Other advantages include increase resident time in ocular tissues and improve patient compliance. However, they are appropriate only for the delivery of hydrophilic drugs due to their high water content. To overcome such a problem emulgel was developed. Emulgel is a combination of emulsion and gel in which hydrophobic drugs could be dissolved in the oil phase of the emulsion.[151617] Several hydrophobic drugs were formulated using emulgel such as diclofenac sodium, miconazole nitrate, and metronidazole.[181920]

Bacterial eye infections are often treated with corticosteroid and antibacterial eye drops. Betamethasone is corticosteroids that help in relieving pain, inflammation, and redness of the eye. Betamethasone sodium phosphate (BSP) is a white powder with molecular weight 516.4 g/mol. It is freely soluble in water and methanol. However, it is practically insoluble in acetone and chloroform.[21]

Levofloxacin is antibacterial drug that is active against both Gram-positive and Gram-negative bacteria and used for the treatment of eye infections.[2223242526] It is a pale yellow solid crystalline powder with a molecular weight of 361.3675 g/mol and melting point of 225°C–227°C. It is freely soluble in glacial acetic acid, chloroform, and sparingly soluble in water.[27] Repeated instillation per day is required for both drugs and a lag time must be left between the two drops when used. This reduce patient compliance and cause low adherence to treatment.[2829] Using emulgel for the delivery of both drugs will eliminate such problems.

The aim and novelty of our work is to formulate an emulgel for the delivery of a hydrophilic and a hydrophobic drug simultaneously. BSP and levofloxacin will be formulated as emulgel and the effect of gelling agent used on the properties of the prepared emulgel will be studied and compared with conventional eye drops of the two drugs. The emulgel formulation will potentially reduce instillation time, increase resident time in ocular tissues consequently improving patient compliance.

MATERIALS AND METHODS

Materials

Levofloxacin, BSP, poloxamer 188 (Sigma Chemical Co. [Aldrich], USA). Xanthan gum, Carbopol 934, Methyl cellulose (HIMEDIA, India). Levofloxacin eye drop (purchased from local pharmacy trade name QUIXIN, company Vistakon). Betamethasone eye drops (purchased from local pharmacy trade name Betnesol™, Company Gsk). All other solutions, chemicals and reagents were of analytical grade.

Methods

Solubility study of levofloxacin in castor oil

The solubility of levofloxacin was studied to determine the maximum amount of levofloxacin that can be dissolved in castor oil. Excess amount of levofloxacin was weighed and mixed with 3 g of castor oil and placed in a stoppered glass vial and agitated on a magnetic stirrer at 25°C for 72 h to reach equilibrium. Thereafter, the solutions were filtered through 0.45 μ filter, diluted suitably with phosphate buffer solution pH 7.4 and evaluated by using ultraviolet (UV) spectrophotometrically for content at 288 nm.[30]

Calibration curve of betamethasone sodium phosphate and levofloxacin

The calibration curves for both drugs were prepared in phosphate saline buffer solution pH 7.4 separately. For levofloxacin, a stock solution of 0.01 mg/mL was prepared and serial dilution was used to construct the curve. The prepared samples were analyzed spectrophotometrically at 288 λ max.[31]

For BSP, a stock solution of 0.037 mg/mL was prepared, and serial dilution was used to construct the calibration curve, and the prepared samples were analyzed spectrophotometrically at 246 λ max.[32]

During the analysis of the release samples, each sample was scanned at wavelength between 200–400 nm and both peaks appear separately during the analysis at 288 λ and 246 λ for levofloxacin and BSP, respectively.

Preparation of emulgel

Emulgel dosage form is generally formulated in three steps which are: preparation of the emulsion phase, preparation of the gel phase, and mixing the two phases for the formation of the emulgel. For the preparation of the O/W emulsion phase, levofloxacin was dissolved in castor oil to form the oil phase. Based on the solubility studies of levofloxacin, 500 mg of levofloxacin was dissolved in 3 g castor oil. Afterward, the aqueous phase was prepared by dissolving of betamethasone, poloxamer 188 (as emulsifying agent), and benzalkonium chloride (as preservative) in distilled water. Both oil and aqueous phases were heated using hot plate magnetic stirrer to 70°C. After heating, the oil phase was dispersed in the aqueous phase with constant stirring at 1500 rpm until a homogenous emulsion was formed. Then, the emulsion was left to cool down at the room temperature. The gel phase was prepared by dissolving the gelling agent in iso-osmotic containing 3% glycerin solution. Different gelling agents were used at different concentrations for the preparation of the gel phase. The final emulgel was prepared by mixing the emulsion and gel phase at 1:1 weight ratio with a high speed mixer for 15 min at 1500 rpm until a smooth homogenous emulgel was formed.[33] The composition of all the formulations prepared is illustrated in Table 1.

Table 1

Compositions of emulgel formulations in weight bases

Formula NO.	Levofloxacin (mg)	Betamethasone sodium phosphate (mg)	Carbopol 934 (g)	Methyl cellulose (g)	Xanthan gum (g)	Castor oil (g)	Poloxamer 188 (mg)	Benzylkonium chloride (g)	Iso-osmotic 3%glycerin	Distilled Water (DW) (g)
F1	500	100	-		1	3	660	0.01	49	Up to 100
F2	500	100	-	-	2	3	660	0.01	48	Up to 100
F3	500	100	1	-	-	3	660	0.01	49	Up to 100
F4	500	100	-	2		3	660	0.01	48	Up to 100
F5	500	100	-	2		3	1320	0.01	48	Up to 100

Evaluation of emulgel

Physical properties

The physical properties of the prepared emulgel formulations were examined. Color, homogeneity, consistency, and phase separation were examined.[33]

pH determination

The pH was determined using pH-meter by positioning the tip of the electrode into the emulgel and after (2 min) the result was recorded.[34]

Rheological study

The viscosity of the prepared emulgels was determined using Brookfield viscometer (Brookfield LV, spindle no. 64). A glass container was filled with emulgel sample, and the spindle of the viscometer was allowed to rotate at predetermined speeds (5, 10, 20, 30, 50, 60, and 100 rpm). For each speed, the viscosity was recorded after 30 s.[35]

Drug content determination

One gram of emulgel sample was dispersed in 100 ml phosphate saline buffer pH 7.4 and sonicated for 2 h. The sonicated mixture was filtrated using 0.45 µm millipore filter and analyzed using UV.[3637]

In vitro drug release study and kinetics

The in vitro release of levofloxacin and BSP from emulgel formulations was performed by modified method using magnetic stirrer and dialysis membrane (M. WT 3500Da). The dialysis membrane was soaked in phosphate saline buffer solution of pH 7.4 for 24 h and opened from both sides. One side of the membrane was tightly closed with elastic rubber, and 1 g of the prepared emulgel (equivalent to 5 mg levofloxacin and 1 mg betamethasone) was placed inside the membrane. Afterward, the open end of the membrane was tightly closed using the rubber band. The membrane was fixed around a glass rod and submerged in a beaker previously filled with 100 ml of phosphate saline buffer solution (pH 7.4) at 37°C ± 0.5°C with stirring rate at 50 rpm. Samples were withdrawn at predetermined time intervals and replaced with fresh buffer, and both drugs were analyzed using UV.[3338] Curve fitting method was used to study the release kinetics of the optimum formula.[39]

Antibacterial activity

In vitro antibacterial activity of the optimum formula (F5) was carried out by using Muller Hinton agar plate, which was prepared by dispersing 28 g of powder in 1 l of deionized water, swirl to mix and sterilized by autoclaving at 15 lbs pressure (121°C) for 15 min then cool it to 47°C, then the medium was poured in sterile plates under a septic condition and was allowed to solidify at the room temperature. Two different types of bacteria were tested; Escherichia coli and Staphylococcus aureus. Accurately 0.1 mL bacterial suspension having a uniform turbidity (106 CFU/mL) was distributed gently over the surface of the medium with a sterile glass spreader. The wells were made aseptically with cork borer having 6 mm diameter. In each of these plates, sufficient quantity of the optimum formula (F5) and levofloxacin eye drop were placed in the pore with the help of syringe, and then the plates were incubated at 37°C for 24 h. The diameters of the inhibition zones were measured in millimeters.[40]

Statistical analysis

Single factor by ANOVA was used to compare the results statistically, and P < 0.05 was considered as statistically significant.

RESULTS AND DISCUSSION

Emulgel dosage form for the delivery of levofloxacin and BSP simultaneously was prepared. All the prepared formulations were yellow viscous creamy preparations with homogeneous appearance. The pH values of the formulations were within the acceptable range [Table 2] which is important to avoid irritation to ocular tissues.[41] In all formulations, castor oil was used as the oil phase. The eye tissues are sensitive especially to oils, and there is limited number of oils that can be used topically. Castor oil is available as eye drops and used previously in the research for eye formulations and that is why it was chosen as the oil for the emulgel.[3342] The solubility of levofloxacin in castor oil was 175 mg/g.

Table 2

The pH values of the prepared emulgel formulations

Formulas	F1	F2	F3	F4	F5
pH	6.91±0.05	6.61±0.015	5.40±0.026	6.41±0.001	6.58±0.023

Effect of gelling agent on viscosity and rheology

Emulgel is a dosage form prepared by mixing emulsion and gel where the drug is dissolved in the emulsion phase. Factors affecting the emulsion such as emulsifying agent will affect drug release from the emulsion to the gel phase. Furthermore, factors affecting the gel properties such as gel type and concentration might affect drug diffusion through the gel once released from the emulsion.

The viscosity study was performed to evaluate the effect of the concentration of gelling agent on the viscosity of the final emulgel formulas. Viscosity measurements give an indication on the rheological properties of the prepared emulgel formulas. From the results obtained in Figure 1, it was noticed that the emulgel formulated with carbopol 934 (F3) has higher viscosity compared to xanthan gum (F1 and F2) and methyl cellulose (F4) which is consistent with previously reported data.[43] The high viscosity of carbopol 934 formulations is due to the crosslinking nature of the polymer chains. Once carbopol neutralized with TEA, they swell and retain large amount of water and consequently higher viscosity of the formulation.[44]

Figure 1

The viscosity of the prepared formulations

All formulations prepared exhibited pseudo-plastic properties in which the viscosity decreased with increasing shear rate. Pseudoelastic behavior is desirable in ophthalmic formulation. During blinking, a high shear is exerted on ocular tissues. If pseudoplastic emulgel is applied, the blinking shear will reduce the viscosity of the formulations and ease their spread on ocular tissues.[45]

Poloxamer 188, which was used as a emulsifying agent, was doubled in F5 to study the effect of the amount of emulsifying agent on viscosity. No significant difference was observed between F4 and F5 (P > 0.05).

Effect of gelling agent on drug content

Drug content was calculated for each formulation prepared [Figure 2]. It was noticed that the drug content was inversely proportional to the viscosity of the formulations prepared. Formulations with high viscosity (F3) have the lowest drug content compared to other formulations. Formulation with methyl cellulose (F5), which has low viscosity, was the formulation with the highest percentage of drug content. The high viscosity may hinder the uniform distribution of the drug through the formulation and cause the variation in drug content.[46]

Figure 2

Drug content % in all formulations

Effect of gelling agent on drug release

Three different gelling agents were used to study the effect of gelling agent type on drug release. The release of drug was compared to commercial eye drops of betamethasone and levofloxacin. The release of both drugs from (F1 to F4) formulations was significantly lower (P < 0.05) compared to the commercial eye drops [Figures 3 and 4].

Figure 3

Drug release of BSP from all the prepared emulgel formulations compared to commercial eye drop of betamethasone

Figure 4

Drug release of levofloxacin from all the prepared emulgel formulations compared to commercial eye drop of levofloxacin

Drug release from formulation containing carbopol 934 (F3) was slow compared to xanthan gum (F1 and F2) and methyl cellulose (F4) which is expected due to the high viscosity of F3 compared to other formulations. After 1 h around 100% of the eye drop was released compared to the emulgel formulations [Table 3]. The release was extended to 6 h for both drugs in all formulations. Higher percentage of drug release was achieved using methyl cellulose as gelling agent (F4). The relatively low viscosity of the formulation allows the drug to diffuse freely through the gel and faster release of the drug was achieved. Based on the above results, F4 was superior compared to F1, F2, and F3.

Table 3

Drug release from commercial eye drops and emulgel formulations after 60 min and 360 min

Formula no	Drug	Time (min)	% drug release	Time (min)	% drug release
Eye drop	Betamethasone	60	94%
Eye drop	Levofloxacin	60	96%
F1	Betamethasone	60	53%	360	85%
	Levofloxacin	60	30%	360	70%
F2	Betamethasone	60	48%	360	80%
	Levofloxacin	60	28%	360	64%
F3	Betamethasone	60	36%	360	67%
	Levofloxacin	60	24%	360	58%
F4	Betamethasone	60	48%	360	92%
	Levofloxacin	60	28%	360	81%
F5	Betamethasone	60	56%	360	96%
	Levofloxacin	60	37%	360	90%

As mentioned earlier factors affecting the emulsion could affect the properties of the emulgel formed. To study emulsifying agent (poloxame 188) on the physical properties of the formulation, the amount of poloxamer was doubled (F5). The physical appearance and the pH were similar in both formulations, and no significant difference (P > 0.05) was observed regarding viscosity behavior as well. The release of both drugs was slightly higher in F5 compared to F4. Doubling the emulsifying agent will produce a uniform distribution of the drug and reduce the surface tension between the oil and water phase. Similar results were previously reported in which the release of itraconazole from the emulgel prepared was enhanced when the total amount of emulsifying agent increased from 5% to 8%.[47] Hence, F5 was the optimum formula for the new combination emulgel.

The release data of the optimum formula for both drugs were fitted to various mathematical models to have better understanding of the release profile from the emulgel. The data were fitted to zero order, first order, Higuchi and Korsemeyer-Peppas model, and the results demonstrated in Table 4. The release of both drugs follow Higushi model because it has the highest regression value (R2). The n value from Korsmeyer-Peppas equation suggests Fickian diffusion of both drugs.[48]

Table 4

Kinetic analysis of betamethasone and levofloxacin from optimum formula (F5)

Optimum Formula	Zero order		First order		Higuchi		Korsmeyer- Peppas
	K0	R2	K1	R2	kH	R2	KKP	R2	n
Levofloxacin	0.181	0.9529	0.0023	0.9235	4.2021	0.9632	8.1414	0.9566	0.3917
Betamethasone	0.1641	0.9541	0.0036	0.9634	3.9256	0.9858	16.955	0.9785	0.2956

Antibacterial activity of the optimum formulation

The antibacterial activity of F5 was tested to eliminate the possible reduction in the activity of levofloxacin due to interference with betamethasone. The inhibition zone of E. coli was 26 and 30 mm for levofloxacin eye drop and F5, respectively, while for S. aureus was 36 and 58 mm for levofloxacin eye drop and F5, respectively. The results indicate that the antibacterial activity of levofloxacin was not compromised in the formula.

CONCLUSION

A new formulation for the delivery of BSP and levofloxacin simultaneously was developed. The factors affecting the physical properties such as gelling agent type, gelling agent concentration and emulsifying agent concentration was studied. Formulation containing methyl cellulose as gelling agent showed promising results compared to other formulations, and the activity of levofloxacin was maintained in the combination. Commercial eye drops of betamethasone and levofloxacin release the drug over 1 h, and the recommended dosage regime to be used is 2 drops up to 8 times a day. However, the emulgel formulation of the same drugs release similar amount to the eye drop over a period of 6 h based on the release studies which potentially will reduce instillation time to two or three times a day instead of eight times. The same amount of drug that was released over 1 h extended to be released over 6 h using the emulgel. The new combination will allow the simultaneous administration and extended release of two drugs which potentially improve patient compliance and adherence to treatment due to reduce instillation time.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.