The current interest shown in novel drug delivery systems (NDDS) by both national and international pharmaceutical firms, pioneering research to devise new strategies for effective delivery of drugs is tremendous. The current global market for NDDS1 is more than €80 billion. The 1950s were the initial stages where the focus was on microencapsulated drug particles. These drug particles were packaged in tiny shells or capsules of dimensions measurable in micrometers and delivered into the body.
A major facelift was brought about with the use of polymers for the manufacture of the capsules or cages in the 1960s. Besides adding to the flexibility and versatility of the process of drug delivery, a few concerns regarding the pulsatile nature of drug delivery were also mitigated. The delivery of drugs to a specific site can be either sustained or pulsatile. The pulsatile mode is however preferred as it closely mimics the in vivo mechanism of release of triggering of repairing agents, as exemplified by the release of hormones. The advent of transepithelial and transdermal delivery strategies in the 1990s has added to the multi dimension nature of the NDDS. The subsequent addition of liposomes at the commencement of this decade has added to the repertoire of existing drug delivery systems. Several strategies are being tried out currently to discover novel carriers for the drugs to be delivered specifically and effectively. Some of the interesting candidates with potential to be deemed as suitable carriers for the novel drugs include Human Serum Albumin (HSA), Silica Gel, Antisense RNA, recombinant DNA and synthetic peptides among others.
Novel drug delivery system2 refers to the use of a delivery device with the objective of releasing the drug into the patient body at a predetermined rate, or at specific time or with a specific release profile, at a desired area of effect.
The NDDS essentially consists of the drug against the causative agent of the disease being treated and a carrier system into which the drug is loaded and transported to site of action. Efforts are now being made to devise carriers that can transport multiple drugs and release them on command.
1.2 TARGETED DRUG DELIVERY SYSTEM:
The aim of drug targeting is to achieve a desired pharmacological response at site without undesirable interactions at other sites.
At present drug targeting is achieved by two approaches.3,5
The first approach is chemical modification of the drug, which is activated only at target site.
The second approach utilises carriers such as liposomes, microspheres, nanoparticles, monoclonal antibodies and macro molecules to direct the drug to site of action.
There are variety of statergies to modify the chemical structure of drug molecules, the most common being the prodrug and most sophisticated being the chemical delivery system approach. A prodrug is an inactive drug that is activated predictably in vivo to the active drug, but with few exceptions it cannot achieve site specific delivery. In contrast, a chemical delivery system involves transformation of the active drug by synthetic means into an inactive derivative which, when placed in the body, will undergo several predictable enzymatic transformations principally at the site of action. This is successful in targeting drug.
Obstacles of target drug delivery4 are because of impermeability of the GI tract to most macromolecules and instability of the drug carrier complex in the hostile environment of the GI tract, administration of large drug carrier complexes is restricted to intravenous or intra arterial injections or to the direct injection into the target site such as tumor. Major obstacle of drug targeting using macromolecules and particulate carriers(Liposomes,Nanoparticles) is rapid sequestering of intravascularly administered drug carrier by mononuclear phagocytes of reticuloendothelial system(RES).So first involves blocking of RES prior to administering the drug carrier, shows some undesirable effects in cancer patients. In recent research nanoparticles for reducing RES uptake is by covalent attachment of PEG uptake is by covalent attachment of PEG to surface of particles and shows increasing circulation time.
A second approach is to impart specificity to the drug carrier by coupling specific ligands onto its external surface. These include monoclonal antibodies, erythrocyte membrane glycoprotein, heated aggregated immunoglobulins. So far, none of these stratergies has proven to be successful due to difficulties in preserving the recognition ability in vivo and avoiding triggering any immunological response.
1.3 COLON SPECIFIC DRUG DELIVERY SYSTEM
The oral route is most popular route of drug administration6,7. For sustained release as well as controlled release systems, the oral route of administration has received the most attention. Patient acceptance of oral administration of drugs is quite high. It is a relatively safe route of drug administration compared with most parentral forms, and the constraints of sterility and potential damage at the site of administration are minimal. Colon-specific drug-delivery systems3 offer several potential therapeutic advantages. In a number of colonic diseases such as colorectal cancer, Crohn's disease, and spastic colon, it has been shown that local is more effective than systemic. Rectal delivery forms (suppositories and enemas) are not always effective because a high variability is observed in the distribution of drugs administered by this route. Therefore, the oral route is preferred. Absorption and degradation of the active ingredient in upper part of the GIT is the major obstacle with the delivery of drugs by the oral route and must be overcome for successful colonic drug delivery. Drugs for which the colon is a potential absorption site (for example, peptides and proteins) can be delivered to this region for subsequent systemic absorption. The digestive enzymes of the gastrointestinal tract generally degrade these agents. However, these enzymes are present in significantly lower amounts in the colon compared with the upper portion of the gastrointestinal tract. Colon-specific drug delivery has been attempted in a number of ways that primarily seek to exploit the changes in the physiological parameters along the gastrointestinal tract. These approaches include the use of prodrugs, pH-sensitive polymers, bacterial degradable polymers, hydrogels and matrices, and multicoating time-dependent delivery systems.
Advantages of Colon Targeted Drug Delivery
Time dependent system: small intestine transit time is fairly consistent.
pH dependent system : formulation8 is protected in the stomach.
It has less side effect.
Unnecessary systemic absorption doesn't occur.
Colon targeted drug delivery can be achieved by both oral and rectal administration.
Colon specific formulations can be used to prolong drug delivery.
It enhances the absorption of poorly absorbed drug.
It helps in efficient vaccine delivery.
Reduces the adverse effects in the treatment of colonic diseases (ulcerative colitis, colorectal cancer, crohn's disease etc.)
Produces a 'friendlier' environment for peptides and proteins when compared to upper gastrointestinal tract.
Minimizes extensive first pass metabolism of steroids.
Prevents the gastric irritation produced by oral administration of NSAIDS.
Disadvantages of Colon Targeted Drug Delivery System
1. Time dependent system:
a) Substantial variation in gastric retention times
b) Transit through the colon is faster than normal in patients with colon
disease.
2. pH-dependent system:
pH in the small intestine and colon may vary between and within the individuals.
pH at the end of small intestine and caecum (colon part) are similar.
Poor site specificity.
3. Microflora activated System:
Diet and disease may affect colonic microflora.
Enzymatic degradation decreases.
Some have been accepted for use in relation to medicines.
1.4 ANATOMY AND PHYSIOLOGY OF COLON
The adult colon is about 5 feet in length. It connects to the small intestine. The major functions of the colon are absorption of water and salts from partially digested food that enters from the small intestine and then send waste out through the anus. What remains after absorption is stool, which passes out when a person has a bowel movement.9
The colon comprises several segments:
the cecum
the ascending colon
the transverse colon
the descending colon
the sigmoid colon
the rectum
The colon is formed during the first 3 months of embryo development. As the foetus grows the abdominal cavity enlarges, bowel returns to the abdomen and rotates, counter clockwise to its final position. The small intestine and colon are held in position by tissue known as mesentery. The ascending colon and descending colon are fixed in the abdominal cavity. The cecum, transverse colon, and sigmoid colon are suspended from the back of the abdomen wall by the mesentery.
Fig 1.1 Large intestine representing parts of colon
Cecum
This is the first part of the colon. It is a dilated region which has a blind end inferiorly and is continuous with the ascending colon superiorly. Just below the junction of the two the ileo caecal valve opens from the ileum. The vermiform appendix is a fine tube, closed at one end, which leads from the cecum. It is usually about 8 to 9 cm long and has the same structure as the walls of the colon but contains more lymphoid tissue.
Ascending colon
This passes upwards from the cecum to the level of the liver when it curves actually to the left at the hepatic flexure to become the transverse colon. The nerve supply is by vagus nerve of the parasympathetic fibers.
Transverse colon
This is a loop of colon that extends across the abdominal cavity in front of the duodenum and the stomach to the area of the spleen where it forms the splenic flexure and curves acutely downwards to become the descending colon.
Descending colon
This passes down the left side of the abdominal cavity then curves towards the midline. After it enters the true pelvis it is known as the sigmoid colon.
Sigmoid colon
This part describes an S-shaped curve in the pelvis that continues downwards to become the rectum.
Rectum
This is a slightly dilated section of the colon about 13cm long. It leads from the sigmoid colon and terminates in the anal canal.
1.4.1 Functions of colon:
In the large intestine absorption ban of water, by osmosis, continues until the familiar semisolid consistency of faeces is achieved. Mineral salts, vitamins and some drugs are also absorbed into the blood capillaries from the large intestine. It is colonized by certain types of bacteria, which synthesize vitamin K and folic acid.They include E.coli, E.aerogenes, S.faecalis and C.perfringens. Hydrogen, carbon dioxide and methane are produced by bacterial fermentation of unabsorbed nutrients, especially carbohydrate. Large number of microbes are present in faeces. In large intestine no peristaltic movement was seen like other parts of digestive tract. Only long intervals a wave of strong peristalsis sweep along the colon transverse colon forcing its contents into descending and sigmoid colons. This is known as mass movement. This combination of stimulus and response is called the gastrocolic reflex.
Usually rectum is empty, but when a mass movement forces the contents of the sigmoid colon into rectum the nerve endings in its walls are stimulated by stretch and assist the process of defaecation.10
Rationale for Colon Specific Drug Delivery
Targeting of drugs to colon is for various reasons11.
Local treatment of inflammatory diseases e.g. crohn's disease.
Colonic diseases can be treated e.g. colorectal cancer and amoebiasis.
Oral delivery of peptides and protein drugs, which normally become inactivated in upper parts the GIT.
Oral delivery of drug substance that have undesirable effects in the stomach and small intestine.
For the treatment of the diseases, e.g. asthma, rheumatic disease and ischemic heart disease.
Delivery of the drugs to the colon is by oral route, is valuable in treating diseases of colon (Crohn's disease, ulcerative colitis, irritable bowel disease and infections) whereby high concentration can be achieved locally used to minimize side effects.
1.5 APPROACHES OF COLON TARGETED DRUG DELIVERY SYSTEM
Most of the conventional drug delivery system are used for treating colon disorders such as inflammatory bowel syndrome (Crohn's disease), infectious diseases (e.g. amoebiasis) and colon cancer are failing to carry the drug in appropriate concentrations to the site of action. From the above-mentioned potential difficulties, different approaches are there for the purpose of achieving colonic targeting and are summarized below.
1.5.1 Prodrug Approach
A prodrug12 is an inactive chemical derivative of a parent compound that is activated predictably in vivo to active drug species at the target site. In this there is a covalent link between parent molecule and carrier molecule. Depending upon the linkage the mechanism for the release of the drug in the colon was decided.
Breakage of linkage in colon is by different enzymes like azoreductase, ß-galactosidase, ß-xylosidase, nitroreductase, glycosidase deaminase, etc.
Examples of prodrugs delivery are:
1. Dexamethasone-2-ß-glucoside and Prednisolone-2-ß-glucoside for delivery of steroids to the colon.
2. Non-essential amino acids (AA) such as glycine, tyrosine, methionine, and glutamic acid were conjugated to salicylic acid. The conjugate showed less absorption and degradation in the upper GI tract and showed more enzymatic specificity by colonic enzymes.
3. Sulphasalazine is the drug, which was used for the treatment of rheumatoid arthritis, having an azo bond between 5-AminoSalicyclicAcid and sulpha pyridine.
1.5.2 Time-Dependent Approach
They are developed to deliver drugs after five to six hours. The lag time13 is dependent on various factors such as dosage form and gastric motility associated with the pathological conditions of the person.
An example of such a dosage form would be an impermeable capsule containing the drug, with hydrogel plug which is used to deliver the drug after a predetermined time. This dosage form, for example Pulsincap, releases the drug once the hydrogel plug hydrates and swells in gastric fluids and the drug is ejected from the device, thereby allowing the release of the drug from the capsule. Another example describes use of a hydrophobic coating material and surfactant in the tablet coating. The release of drug from Time Clock depends on the thickness of the coating layer and is independent on the pH of the GI environment. The rationale behind time-released delivery systems provided that small intestine transit time remains constant. Changes in GIT motility can significantly affect time-release delivery systems to the colon.
1.5.3 pH-Dependent Approach
This approach is based upon the pH-dependent14 release of drug from the dosage form. In this case the pH difference between upper and lower parts of GI tract is effective to deliver drugs to colon. The pH of the intestine and colon depends on many factors such as diet, food, intestinal motility and disease conditions. The knowledge on polymers and their solubility at different pH environments of GIT, delivery systems have been designed to deliver the drug to colon. Commonly used co-polymers of methacrylic acid and methyl methacrylate have been extensively investigated for colonic delivery systems. In vitro evaluation of Eudragit S 100 and Eudragit FS were performed and it was found that the Eudragit FS would be more appropriate for drug delivery.
Inter and intra-subject variability and electrolyte concentration are some of the variables impacting success through this route. In spite of these limitations, pH-based systems are commercially available for mesalazine (Asacol and Salofalk) and budesonide (Budenofalk and Entrocort) for the treatment of ulcerative colitis, Crohn's disease.
1.5.4 Bacteria-Dependent Approach (Polysaccharides as matrices)
The use of microflora as a mechanism of drug release in the colonic region has been of great interest to researchers now a days. The majority of microorganisms14 are present in the distal part of intestinal gut although they are distributed well throughout the GI tract. Endogenous and exogenous substances, such as carbohydrates and proteins, escape digestion in the upper parts of GI tract but they are metabolized by the enzymes secreted by colonic bacteria. Sulphasalazine consisting of the active ingredient mesalazine is a prodrug, was the first bacteria-sensitive drug delivery to the colon. Use of polysaccharides is an alternative substrate for the bacterial enzymes in the colon. Pectin alone or in combination with other polymers has been studied for colon-specific delivery. Pectin, when used alone, was needed in large quantities to control the release of the drug. A coating composition of a mixture of pectin, chitosan and hydroxyl propyl methylcellulose (HPMC) was proven to be very efficient as tablets, coated with this composition passed through the stomach and small intestine and release the drug in the colon.
1.5.5 Pressure or Osmotically-Dependent Approach
Osmotic pressure14 in GIT is another mechanism that is utilised to release the drug in the distal part of the gut. The muscular contractions (i.e peristalsis) of the gut wall generate osmotic pressure, which is responsible for grinding and movement of the intestinal contents. The pressure intensity and duration throughout the GI tract varies. Systems have therefore been developed to resist the pressures of the upper GI tract but rupture in response to the raised pressure of the colon. Capsule shells fabricated from a water-insoluble polymer such as ethyl cellulose, hydroxyl propyl methylcelluose have been used for this purpose.
1.5.6 Multiparticulate Systems
Multiparticulates8 are used as drug carriers in pH-sensitive, time dependent and microbially control systems for colon targeting. Multiparticulate systems have several advantages in comparison to the conventional single unit for controlled release technology, such as more predictable gastric emptying and fewer localized adverse effect than those of single unit tablets or capsules.
A multiparticulate dosage form was prepared to deliver active molecules to colonic region, which combines pH dependent and controlled drug release properties. Microspheres loaded by an enteric polymer (Eudragit S). Here the enteric coating layer prevents the drug release below pH 7.
Table1.1: Materials used in Formulation of Colonic Targeted Drug Delivery System.8
Prodrug Conjugates
pH-Sensitive
Polymers
Materials used in
Time- Dependent
System
Microbial Degradable Polymers
Azobond conjugates
Amino acid
(Polypeptide)
conjugates
Glycoside conjugates
Glucuronide
conjugates and
Sulphate conjugates
Polymeric conjugates
Cyclodextrin
Conjugates
Dextran conjugates
Eudragit L-100
Eudragit S-100
Eudragit L-30 D
Eudragit L-100-55
Eudragit F S 30 D
Poly Vinyl Acetate
Phthalate
Hydroxy Propyl
Methyl Cellulose
Phthalate 50
Hydroxy Propyl
Methyl Cellulose
Phthalate 55
Hydroxy Propyl Ethyl
Cellulose Phthalate
Cellulose Acetate
Phthalate
Cellulose Acetate Trimellate
Hydroxy Propyl
Methyl Cellulose
Hydroxy Ethyl
Cellulose
Ethyl Cellulose
Microcrystalline
Cellulose
Hydroxy Propyl
Methyl Cellulose
Acetate Succinate
Lactose/Behinic acid
Chitosan
Pectins
Guar gum
Dextrans
Inulin
Lactulose
Amylose
Cyclodextrins
Alginates
Locust bean gum
Chondroitin sulphate
Boswellia gum
1.6 Matrix tablets
These are the type of controlled drug delivery systems, which release the drug in a continuous manner. They release the drug by both dissolution and diffusion controlled mechanisms. To control the release of drug, which are having different solubility properties, the drug is dispersible in swellable hydrophilic substances, an insoluble matrix of rigid non swellable hydrophobic materials or plastic materials.
1.6.1 Advantages:
Easy to manufacture.
Versatile ,effective and low cost
Can be made to release high molecular weight compounds
1.6.2 Disadvantages:
The drug release rates vary with the square root of time .Release rate continuously diminishes due to an increase in diffusional resistance or a decrease in effective area at the diffusion front, however, substantial sustained effect can be reduced through the use of very slow release rates, which in many allocations are indistinguishable from zero order.
1.6.3 Classification of matrix tablets:
1.6.3.1 On basis of retardant material used
Hydrohobic matrices :
In this drug is mixed with an inert or hydrophobic polymer and then compressed into tablet .sustain release15 is produced due to the fact that the dissolving drug has diffused through a network of channels that exist between compacted polymer materials. e.g:polyethylene glycol, PVC, EC, and acrylate polymers.
Lipid matrices:
These matrices are prepared by the lipid waxes and related materials. Drug release from such matrices occurs through both pore diffusion and erosion release characteristics are therefore more sensitive to digestive fluid composition with steryl alcohol or stearic acid has been utilized for retardant base for many sustained release formulations.
Hydrophilic matrices:
The formulation of drug in gelatinous capsules or more frequently, in tablets hydrophilic polymers with high gelling capacities as a base excipients, is a particular interest in the field of controlled release .In fact a matrix is defined as well mixed composite of one or more drugs with a gelling agent .these systems are called as swellable controlled systems. e.g of polymers are methylcelluose, hydroxyl propyl methyl cellulose (HPMC), carboxymethylcelluose(CMC),agar-agar, alginates, mannose, galactose, carbopal.
Bio-degradable matrices:
These consist of polymers which comprised of monomers linked to one another through functional groups and have unstable linkage in the back bone. They are biologically degraded by enzymes into monomers that can be metabolized or excreted. e.g: natural polymers such as protiens and polysaccharides, natural polymers, synthetic polymers such as aliphatic poly esters and poly anhydrides.
Mineral matrices:
These consist of polymers which are obtained from species of sea weeds. e.g: alginic acid obtained from brown sea weeds.
1.6.3.2. On the basis of porosity of matrix:
Macro porous system:
In such systems the diffusion of drug occurs through pores of matrix, which are of size range 0.1to 1um.this pore size is larger than diffusant molecule size.
Micro porous:
For this system ore size is 50-200Ao. which is slightly larger than diffusant molecule.
Non-porous matrices:
These are having no pores and the molecule diffuse through the network meshes. In this case polymeric phase exists and no pore phase is present.
1.7 Amoebiasis
Amoebiasis10 is a GIT (Gastro Intestinal Tract) infection spreaded by different species of Entamoeba. The genus Entamoeba is usually found in the intestine of vertebrates and invertebrates. They are characterized by vesicular nucleus containing an endosome (Nucleolus). They are five different species of Entamoeba for which man is host are:
1. E. dispar
2. E. histolytica
3. E. coli.
4. E. gingivalis.
5. E. hartmanni.
E.polecki is usually a parasite of pigs and monkeys, in rare occasions it occur in humans.
1.7.1 Life-cycle of Entamoeba histolytica
Entamoeba histolytica is the best known species parasitizing humans. It was first discovered in 1873 by a Russian clinical assistant D.F.LOSCH. The name of E. histolytica was given by F.SCHAUDINN in 1903.it is a pathogenic intestinal parasite occurring in the colon and rectum, at times, the lower end of the small intestine of humans and causes amoebic dysentery or amoebiasis.
AMOEBIASIS is a term used to mean infection by E.histolytica, whose manifestations may be:
1. Cyst passing
2. Intestinal inflammation
3. Dysentery
4. Hepatitis / brain, lung abscess.
It is a monogenetic having only one host. Its motile adult is called trophozoite and it is typically monopodial, producing one large, finger like pseudopodium at a time. It has two forms, magna pathogenic found in mucosa and sub-mucosa of intestine forming ulcers and minuta, nonpathogenic form found in the lumen of intestine. It has no contractile vacuole. The trophozoite of Entamoeba reproduces mitotically with in the gut of host and turns into cyst form. The mature cyst is called quadrinucleate cyst; it has four nuclei and two chromotoidal bodies, this stage is more infective stage a single cyst can produce 8 amoebulae. In this stage cysts are more resistant to desiccation and even to certain chemicals. Cysts are readily killed by heat and freezing temperatures.
Cysts in water can survive for a month, while those in faeces on dry land can survive for more than 12 days. Symptoms include diarrhea, weight loss, fatigue, abdominal pain, causing lesions and it may reach the blood stream and causes hepatitis, brain, and lung abscess.
1.7.2 Incubation period
From 5 days to several weeks16
1.7.3 Clinical features
Clinically there is a wide range of symptoms associated with intestinal amoebiasis. They are feaces consist predominantly of blood and mucus. Sub-acute diarrhea upto 12 days mixed with much mucus.
1.7.4 Serology
Serology is of great value, especially for the diagnosis of amoebic liver abscess. Since the serum amoebic immuno fluorescent antibody test is nearly always strongly positive with titres of about 1/200 or greater in this condition. The serum cellulose acetate precipitin (CAP) test using amoebic antigens is less sensitive than the immune fluorescent test but is also useful since the CAP test is usually only positive when there is invasive disease. Patients who have only intestinal amoebiasis have lower titers of serum amoebic fluorescent antibody than those with liver abscess.
1.7.5 Identification of species:
Differentiation of species is by using morphologic16 characteristics of cysts and trophozoites. Morphologically E. histolytica, and Entamoeba dispar, are identical there is done by immunologic analysis. Microscopic identification of cysts and trophozoites is the common method for diagnosing E. histolytica.
.
Fig 1.2 Life-cycle of Entamoeba histolytica
1.8 DRUG PROFILE
1.8.1 Metronidazole17
Chemical IUPAC Name : 1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole.
Chemical Formula : C6H9N3O3
:
Molecular Weight : 171.16 g/mol
State : Solid crystalline powder.
Pharmacopoeial Status : I.P.
Melting Range : Between 159-163 °C
Category : Anti-Helico bacterium pylori, Antiamoebic, Antidiarrhoeal.
Dose : 200 mg three times a day for 5 days, or 400 mg, 3times a day for 7 days, Alternative: 2000 mg one time only.
Deescription : White to pale yellow, odorless, crystalline powder.
Solubility : Soluble in water ,methanol, ethanol, chloroform
Experimental
Water Solubility : 10.5mg/ml.
Storage : Store in tightly-closed, light resistant containers.
1.8.2 PHARMACOKINETIC PROFILE
Bioavailability :100%(oral),
59-94% (rectal)
Absorption : Absorbed readily and almost completely from GIT
Distribution : Penetrates well in body tissues and fluids
Metabolism : Hepatic
Half-life : 6-7 hours
Excretion : Renal (60-80%), biliary (6-15%)
Protein binding : 8 - 12 %
Half life : 7.5-8.5 hrs
1.8.3 Mechanism of Action:
Metronidazole18 is selectively toxic to anaerobic micro organisms. After entering the cell by diffusion its nitro group is reduced by certain redox proteins operative only in anaerobic microbes to highly reactive nitro radical which exerts cytotoxicity. The nitro radical of metronidazole acts as an electron sink which competes with the biological electron acceptors of the anaerobic organism for the electrons generated by the pyruvate: ferredoxin enzyme pathway of pyruvate oxidation .The energy metabolism of anaerobes is thus disrupted.
1.8.4 Uses of Metronidazole
Metronidazole is used in
1. Protozoal infections - Amoebiasis
2. Vaginitis due to Trichomonas
3. The post- natal period for the treatment and prophylaxis of infection following caesarian section.
4. Post-partum hemorrhage and other complications of child birth in which infection is a possible hazard.
5. Dental infections 6. Mouth ulcer.
7. Abdominal infections
8.Topical metronidazole for acne and mouth ulcers.
1.8.5 Adverse Effects
Common adverse drug reactions (≥1% of patients) associated with systemic metronidazole therapy include:
Nausea,
Diarrhea, and/or metallic taste in the mouth.
Hypersensitivity reactions like fever, chills etc.
Vomiting, dizziness
Glossitis
Stomatitis,
Dark urine.
1.8.6 Drug Interactions:
Metronidazole increase the bleeding time.
Cimetidine increases blood levels of metronidazole .
Cholestyramine decreases blood levels of metronidazole.
Amprenavir is the drug used to treat human immunodeficiency disease should not combine with metronidazole .Because it causes seizures, increased heart rate, and lead to kidney failure.
Metronidazole in combination with carbamazepine, lithium and cyclosporine show serious reactions.
1.9 POLYMER STUDY
1.9.1 Pectin
Backbone structure
Fig 1.3 (a) A repeating segment of pectin molecule and functional
Groups; (b) carboxyl; (c) ester; (d) amide in pectin chain.
Pectins19 are complex polysaccharides that contain 1,4-linked α-D galactosyluronic residues. Three pectin polysaccharides, homogalacturonan, Rhamnogalacturonan-I and substituted galacturonans, have been isolated from plant cell walls.
Pectin is not a homopolysaccharide and has rhamnopyranosyl residues inserted in the galactosyluronic backbone. Between 20 and 80% of the rhamnopyranosyl residues are, depending on source and method of isolation, substituted at C-4 with neutral and acidic oligosaccharide side chains. The predominant side chains contain large linear and branched α-L-arabinofuranosyl and β-Dgalactopyranosyl residues and their relative proportion and chain lengths may differ depending on plant source. At last minor part of backbone is rhamnogalacturonan-II (RG-II).
Functional Groups:
Pectins contain following groups20 along with nonsugar substituent's, essentially methanol (C2H5OH), acetic acid (CH3COOH), phenolic acids and amide groups. On esterification of galacturonic acid residues with methanol (C2H5OH) or acetic acid (CH3COOH) is a very important structural characteristic. If more than 50% of the carboxyl (COOH) groups are methylated then they are called high-methoxy pectins, and less than 50% degree of methylation are called low methoxy pectins. This same principal applies to acetylation, the degree of acetylation is larger than 100% as galacturonosyl residues can be acetylated with more than one group per monosaccharide. Acetyl groups are generally present in rhamnogalacturonan regions and very low amount in homo galacturonan from apple and citrus fruits. The higher amounts are present in homo galacturonan from potato. In apples a random distribution of the methyl esters groups over the galacturonan backbone was found. For commercial pectins the distribution depends on the raw material and the extraction conditions. Commercial pectins on amidation improves the gelling ability of pectins. In that they need less calcium (Ca) to gel and in high calcium levels gelling ability decreases.
Sources and Extraction
Pectin is found mainly in citrus fruits (oranges, lemons, grapefruits) and apples20. Pectin obtained from citrus fruits is referred to as citrus pectin. Pectins are extracted from peels of citrus fruits and apple pomace by acidified water. Extraction conditions of pH 1.5 to 3.5 and temperature of 60-100 ᶿC for 0.5 to 6 hrs are varied to give a material that has the good gelling capacity and degree of methylation.14
The separation of the viscous material from swollen and disintegrated plant material remains a problem. Washing with ethanol lead to precipitation of intracellular proteins, starches and nucleic acids. Another method of avoiding this contamination is by ball milling at low temperature. Enzymatic degradation of the pectin is decreased by addition of sodium dodecyl sulphate used to remove pigments and lipids. The advantage of alcohol treatment is to the resulting preparation is very suitable for further modification to high methoxylated pectins using acid treatment or to decrease methoxy pectin by treatment with ammonia.
The disadvantage of alcoholic treatment may form hydrogen bonding between cell wall constituents and effect the extraction of the pectins. The extraction method may therefore changed for the type of pectin used. Scientific studies extracted pectins by using galacturonase enzymes. This result in short branched segments, In order to extract unaltered pectins, arabinase and galactanase are used to avoid degradation.21
Table1.2: Availability of Pectin (%) from Different Families 23
Sl.No
Source
% Pectin Present
1.
Lemon Peel
10-15%
2.
Orange Peel
10-12%
3.
Apple Pomace
10-15%
4.
Carrots
10.0%
5.
Sunflower-heads
5.0%
Physical Properties
Colour : Cream or yellowish-coloured powder.
Odour : No odour
Taste : Mucilage like taste.
Uses
1. Pectin is used as a gelling agent, thickening agent.
2. Pectin is also used as a demulcent.
3. Pectin used as stabilizer in cosmetics.
4. Pectin is used in colostomy devices for wound healing.
5. Pectin is used to treat nausea.
1.9.2 EUDRAGIT® S 100
Chemical structure : EUDRAGIT S 100 are anionic copolymer based on methacrylic acid
and methyl methacrylate. The ratio of the free carboxyl groups and
ester groups is approximately 1:2 in EUDRAGIT S 10017.
Molecular weight : 1,35,000.
Description : White powder and having characteristic odour
Solubility : EUDRAGIT S 100 dissolves in 7 g methanol, ethanol, in aqueous
isopropyl alcohol and acetone (containing approx. 3 % water), as well
as in 1 N sodium hydroxide to give clear to slightly cloudy solutions.
EUDRAGIT S 100 are practically insoluble in ethyl acetate,
methylene chloride, petroleum ether and water.
Particle size : At least 95 % less than 0.25 mm.
Film formation : When the Test solution is poured onto a glass plate, a clear film forms
upon evaporation of the solvent.
Residue on
evaporation : At least 95.0 %. 1 g powder is dried in an oven for 6 hrs at 110 °C.
Loss on drying : 5.0 %
Sulphated ash : 0.1 %
Heavy metals : 20 ppm
Storage : Protect from warm temperatures and moisture.
1.10 ENZYME STUDY
Pectinex Ultra SP-L (Pectinase)
Pectinex Ultra SP-L22,24 is a commercial enzyme preparation from Aspergillus aculeatus used in the food industry . It contains different pectinolytic and cellulolytic enzymes pectinase, cellulase, ß-galactosidase, fructosyltransferase, endo-poly-galacturonase, endo-pectinylase and pectin esterase. The enzyme preparation has also been used for the production of fructooligosacharides from sucrose.
