Composition comprising chitosan and an acidic drug for oral controlled release

Description

The present invention relates to an aqueous composition comprising an acidic drug and a hydro- philic polymer having a primary amine functional group.

Controlled-release systems include any drug delivery system that achieves slow release of drug, which is governed by the delivery system over an extended period of time. Controlled released delivery can be classified depending on the routes of administration such as skin, nasal, vaginal and oral. Oral controlled drug delivery is usually made from solid dosage forms including tablets, capsules, mircospheres, granules, and suspensions.

Chitosan (poly(N-acetylglycosamine)) is partially deacetylated chitin which is one of the most abundant polysaccharides in nature second only to cellulose. It has a sugar backbone consisting of β- 1,4 linked glucosamine with a high degree of N-acetylation (70-90% N-acetylglucosamine and 10-30% D-glucose units), a structure very similar to that of cellulose; the only difference being the replacement of the hydroxyl by amino groups.

Chitosan is considered as weak base due to the presence of primary amine group. Thus, it undergoes the typical neutralization reactions of alkaline compounds. Chitosan is insoluble in neutral or alkaline aqueous media. Nearly all aqueous acids dissolve chitosan, some of them are relatively safe for use which allow formation of solutions suitable for making gels.

Acetic acid has been mostly used as a standard solvent for chitosan solutions. Chitosan reacts readily with most aldehydes to form imines. Formaldehyde and gluteraldehyde are considered as cross-linking agents for chitosan. Acyl chlorides react vigorously with chitosan to form the corresponding amide derivatives. Chitosan as it is a natural substance and highly available in nature is inexpensive, non-toxic, biodegradable, biocompatible when compared with other polymers.

Chitosan is considered to be non-digestible by human when taken by oral route, this is due to lack of chitosanases, which are present in some bacteria.

Chitosan acquires a positive charge "cationic polymer" when exposed to acid because of proto- nation of primary amine group. It coagulates, if a negatively charged molecule is added to its solution, e.g. sodium alginate, sulfate and phosphate form conjugates with chitosan. Pharmaceutical uses of chitosan are very numerous. The scientific and medical literature lists hundreds of industrial, medical, and dietary applications for chitosan. These include protection of sensitive drugs from the deactivating enzymes, preparation of artificial cells, using chitosan to trap hemoglobin, promotion of bone repair, burn dressing and contact lens material.

S. T. P. Pharma in Jan-Feb 2000 published a complete thematic issue on "chitosan in drug delivery systems". Also, there are several review articles on chitosan as a drug carrier, such as W. Paul, C. Sharma. Chitosan, a drug carrier for the 21st century: a review. STP Pharma Sci.,10, pp 5-22, 2000; F. Olivia, P. Buri., R. Gury. Chitosan: A unique Polysaccharide for Drug Delivery: a review. Drug Dev. Ind.Pharm. 24, pp 979-993, 1998.

It is an object of the present invention to provide a pharmaceutical composition, preferably a solution, which can be orally administered and wherein the pharmaceutically active ingredient is released in a controlled manner. Thus, a new sustained-release composition having a therapeutically active ingredient shall be provided.

Additionally, a method for its preparation and uses thereof shall be provided.

The first object is achieved by a composition comprising an aqueous solvent and a conjugate of at least one hydrophilic polymer having a primary amine functional group, a derivative or monomer thereof and at least one acidic drug.

Preferably, the polymer is chitosan or the monomer is glucosamine.

In this context, it is also preferred that the acidic drug contains an acidic functional group selected from the group consisting of carboxyhc, sulfonic, nitric, phosphoric group, or a salt thereof

Most preferably the acidic drug is insoluble in water

The acidic drug may be selected from beta lactam antibiotics, quinolone antibiotics, sulfonamide, nonsteroidal anti-inflammatory drugs, anti-hyperhpidimic drugs, psychostimulants, prostaglandin vasodilators, antidepressants, anticonvulsive agents, hemostatic agents, antituberculosis agents, hepatic protectant agents, flavoring agents, sweeteners, antispasmodic agents, anti-neoplastic agents, antiseptic agents, anti-inflammatory cortisone drugs, hypoglycemic drugs, anti-arrythmetic agents, antihypertensive agents, anti-allergy agents, emollients, agents for gastrointestinal disorders and anti-infective

In this regard, the acidic drug may be selected from cephalosporins, penicillins, nalidixic acids, ciprofloxacin, acediasulfone, amfenac, diclofenac, lbuprofen, lndomethacin, acetyl salicylic acid, clinadac, naproxen, mefenamic acid, fosfomycin, bendazac, acifran, fluvastatin, atorvastatin, aceglutamide, alprostadil, amineptine, gamma aminobutyπc acid, gabapentin, valproic acid, aminocaproic acid, aminosalicylic acid, amino acid arginine, aspartic acid, betaine, aspartam, baclofen, bendamustine, bromebπc acid, sodium borocaptate, chlorambucil, methotrexate, bismuth subgallate, dodicin, betamethasone, calcium mesoxalate, capobenic acid, captopπl, cromolyn sodium, spaglumic acid, docusate sodium, mesalamin and flumequine

The composition is preferably characterized in that the aqueous solvent has a pH of 4 to 7, preferably 4 to 6 5

The aqueous solvent may be 0 01 M HCl solution

Preferably, the chitosan has a weight average molecular weight ranging from 20.000 to 1.000 Da.

The composition may further comprise at least one additional therapeutic active ingredient other than the acidic drug as disclosed above.

In this regard it is preferred that the other therapeutically active ingredient is immediately released after oral administration and the acidic drug in the conjugate has a controlled release characteristic. Thus, the composition comprises one or more acidic drugs which are released at a rate suitable for an administration once or twice daily. The composition may optionally comprise one or more other therapeutically active ingredients released immediately in concurrent with the acidic drugs released at a rate suitable for administration of once or twice daily.

Preferably, the composition additionally comprises pharmaceutical excipients selected from the group consisting of sweeteners, coloring agents, preservatives, thickeners and flavoring agents.

According to the invention is also a method for preparing a conjugate of at least one hydrophilic polymer having a primary amine functional group, a derivative or monomer thereof and at least one acidic drug, comprising the steps of reacting the acidic drug to obtain an acid halide, ester, anhydride or other intermediate product, and reacting the intermediate product with the hydrophilic polymer to form a conjugate via amide bond formation.

Preferably the method is carried out under acidic environment.

The composition may be preferably used in the preparation of a medicament for oral administration.

The composition may be also used for the preparation of a medicament having controlled released characteristic for the acidic drug after oral administration.

Surprisingly, it was found that water-insoluble drugs can be solubilised using a conjugate of the water-insoluble drugs together with a hydrophilic polymer having a primary amine functional group, such as chitosan. Therefore, such a water-insoluble drug may be also administered as solution via oral administration. Further, the drug is protected from acidic environment of a stomach but shows its effects after cleavage of the conjugate in the intestine. Additionally, the stomach is also protected from side effects of the drugs in the conjugates and the drug stability is significantly enhanced. The inventive composition may be prepared in a cost effective and easy way.

Additional features and advantages of the subject-matter of the present invention can be taken from the following detailed description thereof with reference to the accompanied drawings, wherein

Figure 1 illustrates the formation of a conjugate comprising chitosan and ibuprofen;

Figure 2 shows a structure of a water-soluble chitosan-acidic drug conjugate system;

Figure 3 shows UV spectra of ibuprofen (A) and ibuprofen ethanoate (B);

Figure 4 shows IR spectra of chitosan (A) and chitosan ibuprofen conjugate (B); and

Figure 5 shows a plasma concentration time profile of ibuprofen, when ibuprofen chitosan solution (amide conjugate) is given to rabbits via oral route in a dose of 90 mg/kg compared to oral ibuprofen solution in a dose of 10 mg/kg.

Chitosan has a wide range of molecular weights. Chitosan of large molecular weight of more than 50.000 Da has low water solubility and forms high viscosity solutions in acidic aqueous medium. Low molecular weight chitosans of less than 50.000 Da are usually water-soluble and form low viscosity solution. Chitosan having molecular weight ranging from 10.000 to 1.000 may refer to as chitosan oligosaccharides. Chitosan oligosaccharide are the most preferred for the present invention.

Chitosan, especially oligosaccharides thereof are known for their high solubility and oral permeability. The conjugation of an acidic drug, such as ibuprofen, can be easily achieved by different chemical reactions. This can be achieved via conversion of ibuprofen to a suitable activated intermediate that can react with chitosan primary amine groups. This intermediate can be achieved by forming an acid halide, ester, anhydride or any activation process known in the art. Upon reacting activated intermediate with chitosan a drug chitosan conjugate is formed. The conjugate was found to be water-soluble. The drug was detected in the plasma of rabbits upon giving the conjugate in the form of oral solution. The mechanism of oral drug release from the solution is not well established. The conjugate might release the active material upon hydrolizing the conjugate via the liver or gut enzymes. The drug local irritation effect was masked by the process of conjugation.

Ibuprofen represents a good model drug for conjugation with chitosan polymer. Ibuprofen is a non-steroidal anti-inflammatory product. The molecular weight is 206. It is practically insoluble in water. Ibuprofen is rapidly absorbed from GIT after oral administration. Peak plasma levels of 15 to 20 mcg/ml occur about 1 hr after administration of a single 200-mg oral dose in fasting subjects. The serum half-life after a single 200 mg oral dose in fasting subjects was about 1.9 hr .

In this invention, the chitosan ibuprofen conjugate provides a sustained release profile after oral administration The plasma concentration time profile of ibuprofen was established to proof the drug release in-vivo using rabbit models, see example 3 below.

Chitosan-ibuprofen conjugate results through the formation of a covalent amide bond, Fig. 1. The amide bond is formed by chemical interactions during solution formulation. Where, ethanol acts as an intermediate for the formation of the amide link i.e. it helps in the formation of an ibu- profen ester that interact with primary amine groups in chitosan polymer to form the amide bond and leaves the solution as a byproduct which is get rid of by evaporation. Acidic environment aids ibuprofen ester formation. In addition, it helps in acidification of free primary amine groups in chitosan (protonation) and so solubilization in aqueous medium. Ibuprofen ethanoate, water insoluble ester, is mixed with chitosan aqueous solution and forms an emulsion. The end point of conjugation is obtained once a homogenous clear solution is obtained. The incomplete amide bond formation between the drug and chitosan is obvious due to the steric hindrance effect. The free primary amine groups are useful to be used as a source for ionization of the free primary amine groups in the chitosan-drug conjugate by the addition of acidic substance such as hydrochloric acid, Fig. 2. This would increase total polymer solubility. A clear solution is to be formed containing the polymer linked with the active material.

When the solution is taken orally, the amide bond is not cleaved in the mouth due to short duration period and absence of amide cleaving enzymes in the saliva.

Examples on the active material related to the invention are beta lactam antibiotics such as cephalosporins and penicillins. Quinolone antibiotics such as nalidixic acid, ciprofloxacin. Sulfonamide such as acediasulfone. Nonsteroidal anti-inflammatory drugs such as amfenac, diclofenac, ibuprofen, acetyl salicylic acid, clinadac, naproxen, mefenamic acid, fosfomycin, ben- dazac. Antihyperlipidimic such as acifran, fluvastatin, atorvastatin. Psychostimulant such as ace- glutamide. Prostaglandin vasodilator such as alprostadil. Antidepressant such as amineptine, gamma aminobutyric acid, gabapentin. Anticonvulsive agent such as valproic acid. Hemostatic agents such as aminocaproic acid. Antituberculosis such as aminosalicylic acid. Hepatic protectant amino acid arginine, aspartic acid, betaine. Flavoring agents and sweeteners such as aspar- tam. Antispasmodic agent such as baclofen. Antineoplastic agent such as bendamustine, brome- bric acid, sodium borocaptate, chlorambucil, methotrexate. Antiseptic such as bismuth subga- llate, dodicin. Anti-inflammatory cortisone drugs such as betamethasone. Hypoglycemic oral drugs such as calcium mesoxalate. Antiarrythmetic agents such as capobenic acid. Antihyperte-

sive agents such as captopril. Antiallergy agents such as cromolyn sodium, spaglumic acid. Emollient such as docusate sodium. GI disorders such as mesalamine. Anti-infective such as flumequine.

Examples

In all examples the chitosan used was purified and activated by washing of chitosan with n- hexane and then ethanol 96% until a clear spectrum in ethanol is obtained by UV spectrum. Then the purified chitosan was completely dried in oven before use to get rid of organic solvents.

Example 1

Conjugation reaction

Chitosan, a natural product obtained mainly from cramps and fish, has a high adsorption affinity towards fatty substances that may attach to its structure during the process of preparation. Thus, purification of chitosan needs the use of organic solvents such as n-hexane and ethanol to get rid of fatty materials or other impurities. These impurities may deactivate the primary amine groups (active sites) present in chitosan. Purification from these impurities may increase the ability for binding to drug molecules.

Ibuprofen (carboxylic acid) was esterified using alcohol (ethanol). Ibuprofen ethanoate (insoluble) was reacted with purified chitosan in an aqueous solution, Fig 1. Slight acidic medium of hydrochloric acid was added to enhance the conjugation process and to solubilize chitosan polymer in aqueous solution. Ibuprofen ethanaote was then reacted with chitosan and a homogenous mixture of ibuprofen-chitosan conjugate was formed.

Example 2

Characterization of conjugation

Infra red spectra were obtained using Fourier transform infra red spectrometer (FTIR). FTIR was performed under room air at room temperature and KBr disk. Samples were placed in an oven at 105 ⁰ C for 3 hours before doing any measurements to get rid of moisture. Approximately 500 mg of KBr and 5 mg of sample powder were blended with pestle and mortar for 5 min. The sample disk was prepared at a pressure of 9 tons for 21 min.

The ultraviolet and infrared spectra of ibuprofen and its ethanoate ester are shown in Fig 3. The spectra differences indicate that there may be a slight difference in the chemical structure. In case of infrared spectra, the large peaks width between 2850-3500 cm-1, which corresponds to hydrogen bonding in ibuprofen carboxylic acid functional groups, decreased tremendously indicating the transformation of the carboxylic acid to ethyl carboxylate of ibuprofen ethanoate ester. A shift in carbonyl functional group for ibuprofen of wave number 1720 to 1740 cm-1 indicates the formation of ibuprofen ethanoate.

The amide bond formation between ibuprofen and chitosan was indicated by physical conversion of the emulsion into a clear transparent solution. In addition, amide bond formation was indicated by the appearance of the carbonyl band at 1740 cm-1 and the C-O band at 1 160 cm-1. Where, these bands were not observed in the IR spectrum of chitosan, Fig 4.

Example 3

In vivo evaluation of drug release

Ibuprofen was conjugated to chitosan having weight average molecular weight of less than 3000 as described in example 1 , where a clear solution was obtained for controlled release delivery Ibuprofen solution unconjugated with chitosan was dissolved in water/propylene glycol mixture, where a clear solution was obtained for immediate release delivery

The conjugate containing ibuprofen and chitosan was given orally to rabbits in a dose of 90 mg of ibupro fen/kg A reference for immediate release oral solution given with a dose of 10 mg of ibuprofen/kg rabbit was also utilized Blood samples were withdrawn at specified time interval, centπfuged at 3500 rpm for 10 minutes and placed in a freezer at -20 ⁰ C The samples were analyzed using HPLC method A simple rapid method of determining the ibuprofen concentration by HPLC was developed Naproxen was used as an internal standard Mobile Phase Water Acetomtπle (40 60), then adjust pH to 2 4 with H3PO4 Column Waters, Symmetry, 5u, C 18, and 150*4 6 mm Internal STD Stock Solution Dissolve 5 mg of Naproxen into 50 ml MeOH Injection Loop 50ul Flow rate 1 ml/min Wavelength 220 nm

Sample Preparation Transfer 100 uL of plasma sample to test tube, Add 10 uL of Internal STD Stock solution. Add 0 25 ml of 1 M HCl, Shake for 30 seconds, Add 5 mL of (85 15)(Hexane Isopropanol) Shake with vortex for 1 mm , Centrifuge at 3000 rpm for 10 mm , Transfer 4 ml of organic layer to new test tube, Evaporate the organic solvent using an air shower, and Reconstitute with 1 ml mobile phase The method was evaluated for specificity showing that there is no interference with the ibuprofen peak Recovery was 85-90% for ibuprofen The calibration curve was linear over the concentration 0 5-10 ug/ml

Figure 5 shows a controlled release behavior for the formula of ibuprofen conjugated with chitosan and an immediate release behavior for formula unconjugated with chitosan

Above results illustrate that ibuprofen shows a zero order drug release as it passes the gastrointestinal tract when given as a covalent conjugate with chitosan.

The features disclosed in the foregoing description, in the claims and in the drawings may, both separately and in any combination thereof, be material for realizing the invention in divers forms thereof.