INTRODUCTION:

Epilepsy is a fourth most common chronic neurological disorder characterized by repeated, unprovoked seizures which are seen in different forms and are consequences of episodic discharge from neurons affecting people of all ages¹. About 50million people worldwide are affected by epilepsy. An individual’s risk in his or her lifetime to develop epilepsy is among 3-5%, with neonates, children whereas the elderly are at a higher risk of acquiring the disorder². An epileptic seizure can be defined as an unexpected rush of electrical activity in the brain. Seizures normally impact the person’s appearance and there acting for a short period of time³. Epilepsy is mainly treated with drugs, although surgery of brain may be used in some cases.

Presently available anti-epileptic drugs are effective in controlling 70% of cases by inhibiting the abnormal discharge from the neurons of the brain thus prevent seizures but their use is limited due to their various side effects. Carbamazepine (CBZ) is first line therapy for the treatment of epilepsy which works by decreasing the nerve impulses that cause seizures and pain. It is used to treat trigeminal neuralgia and bipolar disorders. Based on the Biopharmaceutics Classification System (BCS), CBZ comes under BCS Class II i.e. low solubility and high permeability. CBZ is present in various crystalline forms which has different dissolution, solubility and bioavailability. It is primarily metabolized in the liver to its active state CBZ-10,11 epoxide which is potentially toxic. It is a lipophilic drug (Log P value 2.45) which is poorly water soluble with slower dissolution rate hence shows poor oral bioavailability. Hence, it is most appropriate to design a suitable formulation to enhance the solubility and hence improve the bioavailability of CBZ by using various solubility enhancement techniques. Currently, the oral dosage forms such as tablets, capsules, suspension, cocrystals etc. of CBZ are available^4,5.

Majority of drugs discovered in the recent years belong to the category of BCS-II which poses the greatest challenge in formulation development owing to its poor solubility and hence poor absorption in the gastrointestinal tract. The rate and degree of retention of the medication is determined by the pace and degree of dissolution of drug from any solid dosage forms. For this process of drug absorption, dissolution is considered as the rate-limiting step as on account of inadequate water-soluble drugs. Numerous solubility enhancing techniques have been developed for improving the solubility and also for enhancing the dissolution qualities of marginally water dissolvable drugs for oral delivery. This includes size reduction of the drug by nanonization, cocrystal formation, conversion into inclusion complexes, solid dispersion techniques, self-emulsifying drug delivery systems, liposomes, emulsions and microemulsions but this has to be relevant to all other general drugs. Development of suitable formulation of drugs having poor solubility or poor permeability is one of the main problems nowadays⁶.

Self nano-emulsifying drug delivery systems (SNEDDS) is a lipophilic nano-carrier which is an isotropic mixture of oil, surfactant and co-surfactant spontaneously forming nano droplets upon coming in contact with body fluids^7,8. SNEDDS shows great promise for enhancement of oral bioavailability. It also provides an interfacial region for the portioning between the oil and the gastrointestinal fluid⁹. These systems increase the bioavailability by increasing the drug solubility and maintaining the dissolved state of the drug in the form of oil droplets throughout its movement in the GIT^10,11. Generally, the globule size of a nano-emulsion is obtained between 20 and 200nm when diluted. SNEDDS are more stable and easier to manufacture on a large scale^11,12. Solid dispersion (SD) technique has been one of the attractive methods which involve the dispersion of drug within the carrier matrix constituting a polymer at the molecular level. The drug is dispersed in the matrix in its amorphous form, thus increasing the solubility of the drug, as an amorphous form of the drug shows a greater extent of solubility as compared to their crystalline counterparts. The presence of polymer also imparts stability to the system. Amorphous solid dispersion (ASD) technology has garnered significant attention over a few decades due to the ease of its preparation and the ability to hold a large amount of poorly soluble drug within them. Conversion of drugs into solid dispersion renders them amorphous in nature which is considered to be the reason for the higher magnitude of thermodynamic solubility of ASDs. Solvent evaporation, co-grinding and thermal fusion methods are the prime techniques for manufacturing solid dispersion^13,14. CBZ supersaturatable self-microemulsifying and SD were attempted using PVP K30¹⁵, polyethylene glycol^16,17and phospholipid¹⁸to improve its solubility. Djuris et al. and Lee et al., prepared CBZ-soluplus^® and CBZ-soluplus^®/ D-alpha-tocopherol polyethylene glycol 1000 succinate (TPGS) based SD using hot melt extrusion respectively^19,20. However cost effective self-nanoemulsifying system and SD of CBZ-soluplus^® by fusion method are not attempted till date.

In the present study an attempt was made to formulate cost effective SNEDDS and SD of CBZ which will enhance its solubility and consequently improve the bioavailability for better absorption and therapeutic efficacy.

MATERIALS AND METHODS:

Materials:

The gift sample of CBZ was obtained from Sun Pharma, Vadodara, Gujarat. Gattefosse India Pvt. Ltd. provided free gift samples of Labrafac, Labrasol and Transcutol HP. BASF India Limited provided free gift sample of Soluplus^®. Sunflower oil, palm oil, isopropyl myristate and cinnamon oil were purchased from Genuine Chemicals Co., Mumbai. Tween 20, Tween 60 and Tween 80 were purchased from Nice Chemical Pvt. Ltd., Kerala. Lutrol 300, 400 and 600 were purchased from Signet Chemicals Co. Pvt. Ltd., Mumbai.

METHODS:

Preparation of SNEDDS:

SNEDDS of CBZ was prepared by mixing the different ratios of oil (cinnamon oil), surfactant (tween 80) and co-surfactant (Lutrol 400) to get nanoemulsion. Different ratios of surfactant to co-surfactant (S_mix) and oil to S_mix were tried. The ratio of 1:8 of oil and S_mix (4:1) was optimized based on various trials (Table 1.)²¹.

Preparation of SD:

The solid dispersion of CBZ was prepared by fusion method. In this, CBZ and Soluplus^® (Table 2.) was mixed uniformly and heated until it melted with vigorous stirring. The molten mixture was cooled and allowed to solidify. The obtained solid mass was crushed, pulverized and sieved. The product was stored in desiccator for future use²².

Evaluation of SD:

Solubility Studies:

The solubility studies of CBZ was carried out by adding excess amount of drug in oil, surfactant and cosurfactant separately in eppendorf (n=2) and mixed using vortex mixer. The eppendorfs were then kept at 37°C in water bath shaker for 48 h to reach equilibrium. The collected samples were centrifuged at 5000 rpm for 5 min and the supernatant was diluted with methanol which was analyzed using UV spectrophotometer at 285.6 nm.

Saturation Solubility Studies:

The saturation solubility studies of pure CBZ and CBZ-SD was carried out in water by adding excess amount of drug and formulation in the water separately in eppendorf (n=2) and mixed using vortex mixer. The eppendorfs were then kept at 37°C in water bath shaker for 72 h to reach equilibrium. The collected samples were centrifuged at 5000 rpm for 5 min and the supernatant was diluted with methanol which was analyzed using UV spectrophotometer at 285.6 nm. The saturation solubility studies of optimized formulation were carried out in different buffers such as 0.1 N hydrochloric acid buffer, pH 4.6 acetate buffer and pH 6.8 phosphate buffer using same conditions followed for above studies.

Solid State Characterization:

Fourier Transform Infrared Spectroscopy (FTIR):

Infrared spectroscopy was performed using FTIR-8300 spectrophotometer, Shimadzu, Japan and the spectra were recorded in the region of 4000 cm^-1 to 400 cm^-1. The procedure consisted of dispersing the samples in potassium bromide and compressed into discs by applying a pressure of 5 tons for 5 min in a hydraulic press. The pellet was placed in light path and the spectrum was obtained.

Powder X-ray Diffraction Studies (XRD):

X- ray diffraction (XRD) pattern for pure CBZ and CBZ-SD were recorded on X-ray diffractomer (X’Pert Powder PAN analytical system, Almelo, the Netherlands) with Cu Kα radiation generated at 40 mA and 35 kV.

Table 1. Composition of SNEDDS

Oils	Surfactants	Co-surfactants	Oil to S_mix ratio (Surfactant: co-surfactant)
Labrafac	Tween 20	Transcutol HP	1:1	2:1, 3:1, 4:1, 3:5, 2:3, 5:7
			1:2	3:1
			1:9	3:1, 5:7, 2:1, 4:1, 2:3, 3:5
			1:6	3:1, 2:1
Sunflower oil	Tween 20	Transcutol HP	1:9	3:1, 5:7
Isopropyl myristate	Tween 20	Transcutol HP	1:9	3:1, 5:7
Labrafac	Labrasol	Transcutol HP	1:9	1:0, 3:1, 5:7, 2:1
Palm oil	Labrasol	Transcutol HP	1:3 1:8 1:9	2:1, 3:1 4:1 3:1
IPM	Labrasol	Lutrol 400	4:1	1:10, 1:8
Cinnamon oil	Tween 80	Lutrol 400	1:2 1:4 1:6 1:8 1:10	2:1, 1:2, 4:1, 1:4 2:1, 4:1, 1:2, 1:4 2:1, 4:1, 1:2, 1:4 2:1, 1:4 2:1, 4:1, 1:2, 1:4

In Vitro Dissolution Studies:

In vitro release studies were carried out for pure CBZ and CBZ-SD in three different dissolution media (0.1N HCl, pH 4.6 acetate buffer and pH 6.8 phosphate buffer). 100 mg of pure drug and 500 mg of CBZ solid dispersion (SD3) was compressed in the form of discs/tablet (hardness 1.5 kg/cm²) and dissolution study was carried out using USP type II dissolution apparatus (paddle type) containing 900 ml of respective buffers. The paddle rotation speed was set at 75 rpm. The temperature was maintained at 37 ± 0.5°C by thermostatically controlled water bath. 5 mL of sample were withdrawn at predetermined intervals and the same was replaced with respective buffers. The withdrawn sample was filtered and analysed by UV spectrophotometer at 285.6 nm.

Table 2. Composition of solid dispersion

Sample No.	CBZ (mg)	Soluplus^® (mg)
SD1 (1:2)	500	1000
SD2 (1:4)	500	2000
SD3 (1:8)	500	4000

RESULTS AND DISCUSSION:

Preparation of SNEDDS:

Solubility Studies:

Solubility studies of CBZ were carried out in different oils, surfactant and co-surfactant, and the results are shown in Fig.1. CBZ showed maximum solubility in cinnamon oil followed by Labrafac and palm oil, surfactant Labrasol and co-surfactant Transcutol HP and Lutrol 400. Based on the results, cinnamon oil was chosen as the oil phase, Tween 80 and Lutrol 400 were chosen as surfactant and cosurfactant respectively. Since very less dose (20 mg) could be incorporated in CBZ nanoemulsion prepared using cinnamon oil (oil), tween 80 (surfactant) and Lutrol 400 (co-surfactant) in ratio of 1:8 of oil and S_mix (4:1), they were not used for further optimization.

Fig. 1 Solubility profile of CBZ in different oil, surfactant and co-surfactants

Preparation of SD:

Saturation Solubility Studies:

The saturation solubility studies of pure CBZ and CBZ-SD were performed in water. The solubility of SD3 (1.22 mg/mL) was found to be higher as compared to SD1, SD2 and pure drug (i.e. 0.702±0.033, 0.918±0.076 and 0.228±0.05 mg/mL, respectively).The saturation solubility studies for the pure drug and the optimized batch of SD (SD3) was performed in different buffers such as 0.1 N hydrochloric acid buffer, pH 4.6 acetate buffer and pH 6.8 phosphate buffer and results were found to be0.142±0.002, 0.197±0.001 and 0.155±0.006 mg/mL, respectively for pure drug and 0.0192±0.003, 0.0212±0.002, 0.0237±0.004 for SD3.

Fig. 2 FTIR spectrum of pure CBZ, physical mixture of CBZ and Soluplus® and CBZ-solid dispersion

Fig.3 X-ray diffraction pattern for pure CBZ and CBZ solid dispersion

Solid State Characterization of CBZ-SD:

FTIR:

The FTIR spectra for pure CBZ, physical mixture of CBZ-Soluplus^®, and CBZ-SD is shown in Fig. 2. Characteristic IR peaks for the samples are given in Table 3. The FTIR spectra of CBZ solid dispersion showed two bands at 3464.15, 3161.33 cm^-1 corresponding to the symmetrical N-H stretching and aromatic CH stretching of CBZ, are replaced by a broaden band. This signifies that CBZ has been completely dispersed in Soluplus^® in its amorphous state.

Table 3. Characteristic IR peaks for the sample

Sample	Characteristic IR peaks (Wavenumber in cm^-1)
Pure CBZ	3464.15, 3161.33, 1386.82, 765.74
CBZ- Soluplus^® physical mixture	3464.15, 3161.33, 765.74, 2935.86, 2787.14, 1685.79
CBZ-SD	2860.43, 1739.79, 1685.79

XRD:

Pure CBZ exhibited sharp characteristic peaks at 2θ of 12.7, 15.4, 24.5, and 27.1 degrees (Fig. 3.). Absence of sharp peaks in SD (Fig. 3.) signifies the conversion of CBZ from its crystalline state to amorphous nature during the formation of SD. This may be attributed to the hydrogen bond formation between C=O of CBZ and Soluplus^® increasing the miscibility of CBZ in the polymer.

In Vitro Dissolution Study:

The in vitro dissolution profile for pure CBZ and SD3 batch is shown in Fig. 4. Pure CBZ showed a slower drug release in different dissolution media at end of 120 min. The dissolution profile of SD3 batch clearly indicates a higher drug release than that of pure CBZ. An improved solubility and hence dissolution were observed which may be due to the inherent amphiphilic nature and wetting property of Soluplus®. An enhanced dissolution rate of CBZ-SD could be attributed to the amorphous nature of CBZ dispersed within the matrix of Soluplus^® and increased wettability due to the surface covering of the hydrophilic polymer.

CONCLUSION:

The present study was aimed at improving aqueous solubility of CBZ by using different solubility enhancement techniques. SNEDDS and solid dispersion of CBZ were attempted to improve the solubility and dissolution property of CBZ. However, during the trials it was observed that only a low dose of CBZ could be loaded into the formulation. Hence, SNEDDS were not subjected for further evaluation. The preparation of CBZ SD exhibited success in enhancing the poor aqueous solubility of CBZ, thus improving the dissolution and bioavailability.

ABBREVIATIONS:

CBZ - Carbamazepine,

SNEDDS – Self nano-emulsifying drug delivery system,

XRD - Powder X-ray diffraction studies,

FTIR - Fourier transform infrared spectroscopy,

SD – solid dispersion,

USP – United States Pharmacopoeia,

IR – Infrared,

UV – Ultra-violet,

IPM – Isopropyl myristate

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Received on 29.01.2019 Modified on 18.02.2019

Research J. Pharm. and Tech. 2019; 12(7): 3333-3337.

DOI: 10.5958/0974-360X.2019.00562.6