Physicochemical Characterization of Solid Dispersion of Cefexime with Poloxamer 188

DS Saindane*¹, AS Kulkarni, AN Sagri, RB Pimprikar², SB Yeshwante², CP Suryawanshi², SD Firke³, MK Kale³

¹Department of Pharmaceutical Chemistry, Govt. College of Pharmacy, Karad, (M.S.)

²Gangamai College of Pharmacy, Nagaon, Dhule(M.S.)

³ KYDSCT’s College of Pharmacy, Sakegaon, Tal. Bhusawal, Dist. Jalgaon (M.S.)

ABSTRACT

This study compares the physicochemical properties of cefixime (CFX) solid dispersions prepared by freeze drying method. Solid dispersions of cefixime in poloxamer 188 were prepared and characterized by intrinsic dissolution, powder X-ray diffraction, Fourier transform infrared spectroscopy and Scanning electron microscopy. CFX:Poloxamer 188 solid dispersions showed increased dissolution rate than pure CFX. The Infrared spectroscopic studies showed interaction between CFX and Poloxamer 188 in solid dispersions. The scanning electron microscopy studies showed decrease in particle size of binary system as compared to particle of pure drug. The amorphous state of CFX coupled with presence of interaction between drug and Poloxamer 188. However, the antimicrobial activity of CFX was increased significantly by Poloxamer 188 against S. aureus and E. coli. The solid dispersion technique of CFX:Poloxamer 188 binary system provides a promising way to increase the solubility and dissolution rate of poorly soluble drugs.

KEY WORDS: Cefixime; Solid dispersion; Poloxamer 188; Freeze drying; Dissolution rate; Binary system

INTRODUCTION

In the development of new pharmaceutical product and formulation the Active Pharmaceutical Ingredients (APIs) have played a crucial role. The major objective of formulation is to improve bioavailability, solubility and dissolution rate. The bioavailability of an orally administered drug depends on its solubility in aqueous media. A limiting factor in the oral bioavailability of poorly water soluble compounds is the inadequate dissolution rate. Beneath the conventional method i.e. freeze drying, spray-drying and solvent evaporation new technologies have been recently developed to improve dissolution and aqueous solubility of APIs¹.

Solid dispersions (SDs) of many poorly water soluble drugs with hydrophilic carrier matrix have been formulated for improving drug dissolution rate, which can be further improved if such polymers have surface active properties (Serajuddin , 1999). Solid dispersion may improve the bioavailability of poorly soluble drugs by increasing the drug dissolution rate and their saturation solubility in the gastrointestinal fluids.

Cefixime (CFX) is a semisynthetic antibiotic derived from the secretion of the mold Cephalosporin which resembles, in respect of its structure, the spectrum of organism fighting ability to the third generation cephalosporins of the cefotaxime type^2,3. The drug is highly stable in the presence of beta-lactamases enzymes, as a result, many organisms resistant to penicillins and some cephalosporins may be susceptible to CFX. CFX is employed in the treatment of a variety of respiratory tract infections and otitis media³. CFX and similar drugs of low solubility and high permeability, i.e. “Class II” in the Biopharmaceutical Classification System.

Table 1: Compositions (w/w) of Different Physical Mixture of CFX with Poloxamer 188

Ratio	CFX	Poloxamer 188
1:1	1	1
1:2	1	2
1:3	1	3

Table 2: Compositions (w/w) of Different formulations (Solid dispersion Formulations) of CFX with Poloxamer 188 by freeze drying method

Ratio	CFX	Poloxamer 188
1:1	1	1
1:2	1	2
1:3	1	3

This article described to improve the solubility of cefexime, (6R, 7R)-7-2[2-(2-Amino-4-thiazolyl)glyoxylamido]-8-oxo-3-vinyl-5-thia-1-1azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid, 72- (Z)-[O-(carboxymethyl)oxime] trihyrate. (Fig. 1) by increasing its dissolution rate using freeze drying technology. The active substance was coprecipitated with solubilizing excipient: Poloxamer 188. Poloxamer are polyoxyethylene-polypropylene block copolymer nonionic surfactants that have been widely used as wetting and solubilizing agent, and surface adsorption excipient (Collent and Popli, 2000)⁴. They have been employed to enhance the solubility, dissolution and bioavailability of many poorly water soluble drugs including cefexime using various techniques. Poloxamer 188 is empirically selected to prepare solid dispersion because of its low melting point (about 56-57° C), surfactant properties and oral safety.

Poloxamer (PXM) are amphiphilic non-ionic block polymers of hydrophobic propylene oxide and hydrophilic ethylene oxide (Fig. 2) comprising a central poly(oxypropylene) (PPO) molecules, which is flanked on both sides by two chains of poly(oxyethylene) (PEO) [5]. Various PXMs have similar chemical structures, but they have a variable number of polyoxyethylene and polyoxypropylene units, and there fore, they differ in their molecular weight ⁵. It is used as an emulsifier, solubilizer, dispersing and wetting agent in the preparation of solid dispersion, and for the enhancement of the bioavailability of low-solubility drugs in oral solid dosage forms.^5,6

MATERIALS AND METHODS:

Materials:

CFX was kindly supplied by Emcure Pvt. Ltd (Pune, Maharashtra, India). Poloxamer 188 Loba Chemie Pvt Ltd. (India). All other materials used were of analytical grade.

Methods:

Preparation of solid dispersions and physical mixtures:

CFX and poloxamer 188 were mixed in a mortar and pestle to obtain a homogeneous physical mixture in different ratio and that was sieved through 100 μm mesh.

The formulation with different ratios (Table 2) of CFX were dissolved in nonaqueous solvent and Poloxamer 188 is dissolved in water. Addition of nonaqueous to aqueous system with continuous stirring. Addition rate was maintained 6-8ml/min. Evaporation of nonaqueous phase (dichloromethane) by using Rotary evaporator till drug will precipitate. Drug will diffuse from nonaqueous phase removal of water by freeze-drying precipitated dry product. Product is then passed through sieve No. 100 and stored in dessicator at room temperature until use⁷.

Fig. 1: FTIR spectra of CFX–Poloxamer 188 formulation: (a) CFX; (b) Poloxamer 188; (c) Physical mixture and (d) B3 Formulation

Solubility measurements of CFX:

Solubility measurements were performed according to the method of Higuchi and Connors (1965). An excess amount of solid dispersion was added in 10ml distilled water taken in test tubes. The samples were sonicated for 1 hr at room temperature. Thereafter, the capped test tubes were shaken at 25 or 45±0.1°C for 24 hrs in rotary flask shaker. Subsequently, the suspensions were filtered through Whatman filter paper no. 41, and the filtered solutions were analyzed spectrophotometrically at 288 nm⁷.

Dissolution studies:

In vitro release profile for each solid dispersion as well as plain CFX were performed using USP eight station dissolution test apparatus (Lab India) employing USP type I apparatus. Dissolution study was carried out in a 900 ml of pH 7.2 buffer at 37 ± 0.5 °C at 100 rpm. Five ml samples were withdrawn at time intervals of 5, 10, 15, 20, 25, 30, 35, 40, 45 and 60 min. the volume of dissolution medium was adjusted to 900 ml by replacing each 5 ml aliquot withdrawn with 5ml of fresh pH 7.2 phosphate buffer. The concentrations of drug in samples were determined by measuring absorbance at 288 nm. Cumulative percent drug released was determined at each time interval. Pure CFX was used as control⁷.

Powder XRD:

Samples were evaluated by using a Philips Analytic X-Ray—PW3710 (Holland) diffractometer with tube anode Cu over the interval 5–80°/2θ. The operation data were as follows: generator tension (voltage) 40 kV, generator current 30mA and scanning speed 2°/min. X-ray powder diffractometry (XRD) were used to characterize the solid-state properties of CFX⁸.

Table 3: Saturation Solubility Study of the formulations

Systems	Saturation solubility (µg/ml)*
Pure drug	0.273 ± 0.06
B1	0.475 ± 0.08
B2	0.529 ± 0.05
B3	0.611 ± 0.05

* Indicates mean of three experiments; B1: formulation (CFX:Poloxamer 188) (1:1); B2: formulation (CFX:Poloxamer 188) (1:2); B3: formulation (CFX:Poloxamer 188) (1:3)

Fig. 2: XRD patterns of CFX-Poloxamer 188 formulation: (a) CFX; (b) Poloxamer 188; (c) Physical mixture and (d) B3 formulation

FTIR spectroscopy:

Infrared spectra were obtained using a Jasco 5300 FTIR spectrometer using KBr disks. The samples were previously ground and mixed thoroughly with KBr. The KBr disks were prepared by compressing the powder. The scanning range was kept from 4600 to 400cm−1⁹.

Results and discussion:

Fourier transformation-infrared spectroscopy:

FT-IR analysis (Fig. 2) the possibility of an interaction of CFX with Poloxamer 188 in the solid state. Figure 1 illustrates the FTIR spectra of CFX, Poloxamer 188, PM and CFX–Poloxamer 188 (1:3) B3. IR spectrum of CFX (a) is characterized by principal absorption peaks at 3365 cm−1 (N-H stretch), 2923 cm−1 (C-H), 1770 cm−1 (C=O stretching acid/ester), 1668 cm−1 (C=O stretching amide), 1592 cm−1 (C=N stretching), 1382 cm−1 (N-O stretching).

The IR spectrum of PM (c) shows peaks of both CFX and Poloxamer 188 with decrease in the peak intensity. However some peaks of CFX at 2876,2254,1684,1541 and at 1109 cm−1 were disappeared indicating strong physical interaction of CFX with Poloxamer 188. In the IR spectra of binary system B3 (d) the peaks of CFX at 2878,1685,1149,1111 and at 962 cm−1 completely disappeared indicating that cephem ring with carboxylic functional group of guest had been entrapped in the hydrophobic cavity of host molecule. These changes occurred in IR spectra of B3 indicated formation of complex in solid state¹⁰.

Table 4: % drug release in different formulations

Time	Cumulative % Drug Release*
Time	Drug	B1	B2	B3
5	12.36 ± 1.2	28.23 ± 3.4	31.15 ± 2.4	31.54 ± 1.8
10	21.05 ± 3.6	40.85 ± 1.7	41.29 ± 2.2	45.67 ± 2.1
15	32.43 ± 5.1	44.53 ± 2.2	47.77 ± 1.4	53.08 ± 2.4
20	35.73 ± 3.1	51.10 ± 2.3	58.43 ± 3.3	62.47 ± 1.9
25	39.79 ± 2.2	61.45 ± 1.1	63.56 ± 1.6	67.66 ± 1.6
30	43.45 ± 3.5	69.65 ± 4.3	73.56 ± 3.2	74.66 ± 2.2
35	47.07 ± 3.7	72.83 ± 0.8	77.89 ± 2.6	83.39 ± 3.1
40	54.26 ± 2.4	80.24 ± 1.9	86.00 ± 4.2	88.79 ± 2.4
45	61.14 ± 1.9	85.53 ± 5.3	93.93 ± 3.8	95.72 ± 1.5
60	64.30 ± 3.5	93.68 ± 4.2	97.56 ± 1.5	99.59 ± 0.9

*Indicates mean of three experiments; B1: formulation (1:1); B2: formulation (1:2); B3: formulation (1:3)

X-ray powder diffractometry:

The solid state of CFX, carrier and solid dispersion of CFX were studied by XRD (Fig 3). The XRD pattern of CFX showed peaks that were intense and sharp, indicating its crystalline nature. Crystallinity was determined by comparing some representative peak heights in the diffraction patterns of the formulation with those of a reference. The powder diffraction patterns (PDP) of pure CFX showed characteristic high-intensity diffraction peak between 9.05˚2θ to 26.45 ˚2θ range. The PDP of the formulation did not show peaks corresponding to CFX thus indicating that formulation was in amorphous form¹¹.

SEM:

SEM micrographs of the conventionally crystallized drug showed narrow needle like crystals (Fig. 4a). CFX with Poloxamer 188 (B3 formulation) look like irregular shape and loose aggregate, indicating presence of amorphous form. Therefore, it is possible that the reduced particle size, increased surface area and the close contact between the hydrophilic carrier and the drug may be responsible for the enhanced drug solubility and dissolution rate observed for the solid dispersion¹².

Saturation solubility studies:

All formulation of CFX showed enhancement in the aqueous solubility as compared to pure drug alone (Table 3). The 1:3 ratio of CFX with Poloxamer 188 showed higher solubility than all other ratios of CFX. The enhancement in the solubility of complex is mainly attributed to the formation of stable amorphous system of CFX with Poloxamer 188. These sample solutions were analyzed using Shimadzu-1700 UV/VIS Spectrophotometer at 288nm¹⁴.

Dissolution rate studies:

All the formulations of CFX prepared by freeze drying method showed faster dissolution as compared to pure drug alone (Table 4). The rapid dissolution of CFX from solid dispersion may be attributed to molecular and colloidal dispersion of drug in hydrophilic carrier matrix. Dissolution rate of pure CFX is less because of hydrophobic nature of drug.

The formulation B3 ratio (1:3) showed faster dissolution as compared to 1:1 and 1:2 ratios in solid dispersions (Fig. 5). This may be due to increased proportion of water soluble carriers in solid dispersions. As soluble carrier dissolves, the insoluble drug gets exposed to dissolution medium in the form of very fine particles for quick dissolution¹⁷.

From above observations, it was concluded that CFX:Poloxamer 188 formulation ratio 1:3 showed fastest dissolution as compared to other formulations. The dissolution rate increase for binary system was due to greater hydrophilicity, higher wetting effect, mechanical treatment, which increased the contact between the drug and the carrier and ability to form stable complex¹⁸.

Antimicrobial studies:

The antimicrobial activity of all formulations of CFX with Poloxamer 188 against Gram-positive (S. aureus) and Gram-negative (E. coli) species was checked by cup-plate method and compared with the pure CFX. The results are summarized in Table 5. These studies revealed that all binary systems of CFX have shown greater antimicrobial activity than CFX alone¹⁹.

Fig. 4: Binary system dissolution profile

CONCLUSIONS:

Solubility and dissolution rate of CFX were enhanced by preparing CFX with Poloxamer 188 in relatively easy, simple, quick and reproducible manner using freeze drying method. Immediate release of free CFX from formulations resulted into rapid absorption and improved bioavailability compared to pure CFX. Preliminary results from this work suggested that the preparation of immediate release CFX formulation by freeze drying method using poloxamer 188 as a hydrophilic polymer carrier could be a promising approach to improve solubility, dissolution and absorption rate of CFX. Further, it is found that carrier can also improve the antimicrobial activity of CFX in vitro by increasing its release rate.

ACKNOWLEDGEMENTS:

The authors are thankful to Emcure Pvt. Ltd. (Pune, India) for providing gift sample of cefixime. Authors are very much thankful to Principal, Govt. College of Pharmacy, Karad, Maharashtra, India for providing laboratory facilities and constant encouragement.

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Received on 13.05.2009

Accepted on 10.06.2009

Research Journal of Pharmaceutical Dosage Forms and Technology. 1(2): Sept.-Oct. 2009, 161-166

System	Zone size (mm)*
System	E-Coli	Standard Deviation (S.D.)	Staphylococcus aureus	Standard Deviation (S.D.)
Pure Drug	21.65	0.3815	21.16	0.3971
B3	26.72	0.4601	27.18	0.5419