INTRODUCTION:

The main purpose of oral controlled drug delivery system is to provide therapeutically effective plasma drug concentration for a longer period of time and thereby reducing the dosing frequency and minimizing fluctuations in plasma drug concentration at steady-state by delivering the drug in a controlled and reproducible manner¹. But this is difficult due to number of physiological problems such as fluctuation in the gastric emptying process, narrow absorption window and stability problem in the intestine². To overcome these problems, different approaches have been proposed to retain dosage form in stomach. These include bioadhesive or mucoadhesive systems³, swelling and expanding systems^4,5, floating systems^6,7 and other delayed gastric emptying devices.

The concept of mucoadhesion was introduced into controlled drug delivery in the early 1980s. Mucoadhesion is the attachment of a natural or synthetic polymer to a biological substrate. It is an important new aspect of controlled drug delivery⁸. There has been increased interest in recent years in using mucoadhesive polymers for drug delivery^9,10. Substantial effort has recently been focused on placing a drug or a formulation in a particular region of the body for extended periods of time. This is needed not only for targeting of drugs but also to better control of systemic drug delivery ¹¹.

Ciprofloxacin is a synthetic fluoroquinolone derivative with broad spectrum antibacterial activity¹². It is widely used in the treatment of urinary tract infections, lower respiratory tract infections, bacterial diarrhoea, skin and soft tissue infections, bone and joint infections, gonorrhea and in surgical prophylaxis¹³. In most of the cases, it would appear that for treatment of above said infections, physicians prescribe ciprofloxacin as a first choice of drug.

The average time required for a dosage unit to traverse the GIT is 5-7 hr and drug will experience a pH range from 1 to 8 as it travels through the GIT. A drug must be in a solubilized and stable form to successfully cross the biological membrane, but ciprofloxacin is described as soluble in lower pH and insoluble in pH 6.8. Experimental solubility at pH 3-4.5 is 10-30 mg/mL¹⁴and the lowest solubility at pH 6.8 is 0.0813mg/mL¹⁵ .So ciprofloxacin is a best candidate for mucoadhesive drug delivery system as in this region it will dissolve and absorb rapidly.

In the present study bilayer tablets of ciprofloxacin hydrochloride containing an immediate release layer and a mucoadhesive extended release layer were prepared and evaluated. Carbopol 934P, Hydroxylpropylmethylcellulose -15 cps (HPMC-15cps), Methocel K4M and Sodium Carboxymethylcellulose (Na-CMC) were used as mucoadhesive polymer. Release profile was compared with a commmercial product.

MATERIAL AND METHODS:

Materials:

Ciprofloxacin Hydrochloride was a kind gift from Incepta Pharmaceuticals Ltd, Bangladesh. Carbopol 934P was obtained from Noveon, Mumbai, hydroxylpropylmethylcellulose -15 cps (HPMC-15cps) was obtained from Signet chemical corporation, Mumbai, India, and Methocel K4M was obtained from Colorcon Asia Ptv. Ltd. Sodium carboxy methylcellulose (NaCMC) and Other excipients, avicell PH 101, lactose, magnesium state, purified talc and aerosil 200 were procured commercially and were used as received. Acetonitrile and methanol were of HPLC grade and were purchased from E. Merck, Darmstadt, Germany. Ammonium acetate, acetic acid and other reagents were of analytical-reagent grade and purchased from E. Merck, Darmstadt, Germany. Water was deionised and double distilled.

Preparation of mucoadhesive bilayer tablets:

Mucoadhesive bilayer tablets were prepared by direct compression method. The powder mixture was passed through sieve # 22 and lubricated with magnesium stearate, purified talc and aerosil-200 by blending for 10 min. Tablets were compressed in 13 mm-diameter die of an infrared hydraulic press with a compression force of 4 ton. Mucoadhesive layer was compressed first followed by immediate release layer.

Table 1: Composition of immediate release layer of ciprofloxacin bialyer tablet

SL. No.	Ingredients	Amount (mg/tablet)
1.	Ciprofloxacin (as Hydrochloride)	250
2.	Lactose	200
3.	Magnesium Stearate	1

Evaluation of tablets:

All prepared mucoadhesive tablets were evaluated for its uniformity of weight, hardness, friability and thickness according to official methods.¹⁶ The average weight and percentage deviation were calculated by weighing 10 tablets from each brand by an analytical weighing balance (AY-200, Shimadzu, Japan). The crushing strength was determined with an Automatic Tablet Hardness Tester (8M, Dr Schleuniger, Switzerland). Ten tablets of each brand were weighed and subjected to abrasion by employing a Veego friabilator (VFT-2, India) to determine friability.

Table 2: Composition of different mucoadhesive sustain release layer of ciprofloxacin bialyer tablet

SL. No	Ingredients	F-1	F-2	F-3	F-4
1.	Ciprofloxacin (as Hydrochloride)	250	250	250	250
2.	Carbopol 934P	200	--	--	--
3.	HPMC 15 cps	--	200	--	--
4.	Methocel K4M	--	--	200	--
5.	Na-CMC	--	--	--	200
6.	Lactose	50	50	50	50
7.	Magnesium Stearate	1	1	1	1
8.	Aerosil-200	1	1	1	1
9.	Purified Talc	1	1	1	1

Drug content:

Five tablets were powdered in a mortar. An accurately weighed quantity of powdered tablets (100 mg) was extracted with 0.1N HCl (pH 1.2 buffer) and the solution was filtered through 0.45 μ membranes. Each extract was suitably diluted and analyzed by a Shimadzu HPLC system. The drug analysis data were acquired and processed using LC solution (Version 1.2, Shimadzu, Japan) software running under Windows XP on a Pentium PC. 0.025M ortho-phosphoric acid (pH = 3.03), methanol and acetonitrile in 50:15:35 ratio was used as mobile phase. Flow rate was 1.5 mL/min, injection volume was 20 μL and λmax of UV detection was 278 nm. Temperature was kept ambient (30 °C) and the sensitivity was 0.0005. Retention time of ciprofloxacin was found to be at 1.76 min.

Measurement of ex-vivo mucoadhesive strength:

Bioadhesive strength of the ciprofloxacin tablets was measured by a modified physical balance. A piece of goat stomach mucosa was pasted to a petri-dish with cyanoacrylate adhesive and the mucus membrane was wetted with 2-3 drops of 0.01 N HCl. The tablets were tied with thread and attached with the mucus membrane. Another end of thread was tied with one side of the physical balance. The weight required to detach the tablet from the mucosal surface was taken as the measure of mucoadhesive strength. Force of adhesion was calculated from the mucoadhesive strength as per following equation.

Force of adhesion (N) = (Mucoadhesive strength × 9.81) ÷ 1000

Measurement of ex-vivo residence time:

Modified USP disintegration apparatus was used to determined ex-vivo residence time. The disintegration medium was composed of 800 mL 0.01 N hydrochloric acid (pH 1.2) maintained at 37±0.5°C. A segment of goat stomach mucosa was pasted to the surface of the beaker, vertically attached to the apparatus. The mucoadhesive tablet was than pasted to the mucosal membrane by applying a light force with a finger trip for 30 seconds. Then the tablet and mucosa was hydrated with the medium. The apparatus allowed moving up and down so that the tablet was completely immersed in the buffer solution at the lowest point and was out at the highest point. The time for complete erosion or detachment of the tablet from the mucosal surface was recorded as the mucoadhesion time.

In vitro drug release study:

In-vitro drug release studies were carried out using USP XXII dissolution apparatus type II (Electrolab, Mumbai, India) at 50 rpm. The dissolution medium consisted of 900 ml of 0.1N HCl (pH 1.2), maintained at 37±0.5ºC. The dissolution samples were collected at pre-determined time interval and replaced with an equal volume of 0.1N HCl to maintain the volume constant. The sample solution was diluted sufficiently and analyzed at 278 nm using an UV spectrophotometer ((UV 1700, Shimadzu, Japan)). The study was performed in triplicate.

RESULTS AND DISCUSSION:

Physicochemical evaluation of mucoadhesive tablets:

Tablets were prepared by direct compression method using Carbopol 934P, Hydroxylpropylmethylcellulose -15 cps

(HPMC-15cps), Methocel K4M and Sodium Carboxymethylcellulose (Na-CMC) as mucoadhesive polymer. The formulation had low tablet weight variation (% deviation < 0.6). Crushing strength of the tablets was in the range 165 to 178 N and percentage weight loss in the friability test was ≤ 0.5% in all the batches. Drug contents of the tablets in all the batches showed 490 mg to 507 mg instead of 500 mg. Overall, the prepared tablet batches were of good quality with regard to crushing strength, friability, weight uniformity and drug content.

Table 3: Mucoadhesive strength (gm), force of adhesion (N) and residence time (hr) of tablets

Parameters	F1	F2	F3	F4
Mucoadhesive Strength (gm)	61.811	63.04	74.5	54.3
Force of Adhesion(N)	0.6	0.61	0.73	0.53
Mucoadhesion Time(hr)	6.75	3	8.5	6

Table 3 showed the mucoadhesive strength, force of adhesion (N) and mucoadhesion time (hr) of different formulation. The highest mucoadhesive strength as weal as highest force of adhesion was observed with formulation F-3 prepared with Methocel-K4M followed by F-2 (HPMC-15cps ) and F-1 (Carbopol 934P). Ex vivo mucoadhesion time for F-1 to F-4 varied from 3 to 8.5 hours. Highest residence time was found with F-3 containing Methocel K4M whereas HPMC-15cps showed lowest residence time among all the formulation.

In vitro release study:

The results of dissolution studies are graphically represented in Figure 1. All dissolution data are based on the actual drug content of the test tablets as calculated from the assay results. Inter-brand (brand to brand) variations in dissolution profiles were observed. Commercial product released more than 50% drug within 15 minutes whereas Methocel-K4M based formulation (F-3) released only 8% within 15 minutes. 100% drug was released within two hours from reference product. At this time point HPMC-15 cps released 90% ciprofloxacin. Higher sustained drug released was found from Methocel K4M based formulation (F-3). From this formulation drug release was completed within 7 hours. HPMC-15cps and Na-CMC based formulation released 100% drug within 3 hours and Carbopol 934P based formulation released 100% drug within 5 hours.

Figure 1: Drug release profile of mucoadhesive tablets F1-F4 and commercial product (CP)

Drug Release Kinetics:

The drug release data were fitted to models representing zero order (cumulative amount of drug released vs. time), first order (log percentage of drug unreleased vs. time), Higuchi’s (cumulative percentage of drug released vs. square root of time), and Korsmeyer’s equation kinetics to know the release mechanisms. The results were shown in table 4.

Figure 2: Mean dissolution time (MDT), time required for 50% drug release (T50%) of mucoadhesive tablets F1-F4 and commercial product (CP)

Comparison of drug release:

Mean dissolution time (MDT), time required for 50% drug release (T50%) were calculated and presented in figure 2. MDT is used to characterize the drug release rate from the dosage form and the retarding efficacy of the polymer. A higher MDT indicates a higher drug-retarding ability of the polymer and vice versa. The MDT value was found to be a function of polymer loading. As the release rate of F-3 and F-1 were slowest, the MDT values of them were highest (2.74 h and 1.22 h respectively). The lower MDT values of F-2 and F-4 (0.86 h and 0.94 h respectively) indicate the rapid release of drug. Time required for 50% drug release was also shown in Fig 2. T50% was found proportional to MDT (R² = 0.982).

DISCUSSION:

The present study was aimed to make gastro retentive dosage form to release the drug in sustained manner in gastric fluid.

The ciprofloxacin mucoadhesive tablets were off-white, smooth and flat shaped in appearance. The results of hardness and friability were an indication of good mechanical resistance of the tablets. The weight variation test showed satisfactory results as per Indian Pharmacopoeia (IP) limit. Good uniformity in drug content was found among different formulation of the tablets.

The difference of mucoadhesive properties of different formulation could be attributed to the incorporation of various types of polymers, which affected the mucoadhesion. The maximum mucoadhesion strength of Methocel K4M in F-3 is 74.5gm. Methocel K4M offers a number of important properties for mucoadhesion—water solubility, hydrophilicity, high molecular weight, hydrogen bonding functionality and good biocompatibility. These polymer have a long linear chain structure which allows them to form a strong interpenetrating network with mucus thus shows highest mucoadhesive strength among all the formulation. The formulation-1 containing Carbopol 934P showed good mucoadhesive strength of 61.811gm for 3 minutes contact time. This high bioadhesive strength of Carbopol 934P may be due to the formation of secondary bioadhesion bonds with mucin and interpenetration of the polymer chains in the interfacial region.

Drug release data showed that the drug release from reference tablet was sustained only for 2 hours whereas drug release from the formulated tablets was sustained for 3 to 7 hr. Methocel K4M based formulations (F-3) (100% in 7hr) show reasonable drug release when compared to other formulations. This might be due to high viscosity polymer Methocel K4M maintains the integrity of the tablets for longer duration by reducing the effect of erosion thus resulting in increase in bioadhesion time. The another reason is that Methocel K4M increases in diffusion path length and the drug molecule needs more time to travel the path.

As per table 4 all the formulations in this investigation could be best expressed by Higuchi’s classical diffusion equation, as the plots showed high linearity (R² : 0.942 to 0.988) which indicates that the drug release follows diffusion mechanism. To confirm the diffusion mechanism, the data were fitted into Korsmeyer– Peppas equation. All the formulations showed n values ranging from 0.45 to 0.67, indicating non-Fickian/anomalous diffusion.

CONCLUSION:

All the four formulations of ciprofloxacin mucoadhesive tablets showed good results in case of physicochemical parameters. The four formulations showed uniform weight, thickness crushing strength and uniformity of content. But no similarity observed in the release pattern of ciprofloxacin from the four formulations. Commercial product released 100% drug within 2 hour. Whereas F-1, F-2, F-3 and F-4 needed 5 hr, 3 hr, 7 hr and 3 hr respectively to release 100% drug. So Methocel K4M based formulation may be used to produce mucoadhesive bilayer tablets for higher sustained release of drug. However in vitro dissolution test in three pH levels ( 1.2, 4.5 and 6.8) and probably in vivo test may be required for final selection of formulation.

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Received on 20.08.2011 Accepted on 27.08.2011

Asian J. Pharm. Res. 1(3): July-Sept. 2011; Page 64-68

Formulation code	Zero order		Higuchi		First order		Korsmeyer
Formulation code	K_°	R^²	K_H	R^²	K₁	R^²	n	R^²
F-1	16.67	0.786	44.18	0.942	-0.31	0.972	0.49	0.847
F-2	41.13	0.892	64.16	0.988	-0.45	0.977	0.57	0.959
F-3	14.69	0.853	42.18	0.971	-0.22	0.985	0.66	0.891
F-4	26.25	0.795	56.19	0.944	-0.67	0.793	0.55	0.817
Commercial product	42.69	0.805	69.31	0.966	-0.83	0.959	0.45	0.933