Fast dissolving drug delivery systems have rapidly gained acceptance as an important new way of administering drugs. There are multiple fast-dissolving OTC and Rx products on the market worldwide, most of which have been launched in the past 3 to 4 years. There have also been significant increases in the number of new chemical entities under development using a fast-dissolving drug delivery technology.
Rapidly dissolving dosage forms have acquired great importance in the pharmaceutical industry because of their unique properties. Rapidly dissolving dosage forms are also called quick-dissolving delivery systems; quick-disintegrating, orally disintegrating, mouth dissolve dosage forms; or melt-in-mouth dosage forms. However, the function and concept of all these dosage forms are similar. In less than one minute, these dosage forms disintegrate or dissolve in the salivary fluids of the oral cavity, releasing the drug and inactive ingredients. Most of the drug is swallowed with the saliva where subsequent absorption takes place in the gastrointestinal tract. By definition, a solid dosage form that dissolves or disintegrates quickly in the oral cavity, without the need for the administration of water, is known as an oral fast-dissolving dosage form.
Salient Features of Fast Dissolving Drug Delivery System
Fast Dissolving Delivery Systems are easy to administer and handle hence, leads to better patient compliance. Usually, elderly people experience difficulty in swallowing the conventional dosage forms (tablets, capsules, solutions and suspensions) because of tremors of extremities and dysphasia. Fast Dissolving Delivery Systems may offer a solution for these problems.
1.2.2 Taste of the medicament
As most drugs are unpalatable, mouth dissolving delivery systems usually contain the medicament in taste masked form. Delivery systems dissolve or disintegrate in patient’s mouth, thus releasing the active ingredients which come in contact with the taste buds and hence, taste masking of the drugs becomes critical to patient compliance.
1.2.3 Hygroscopicity
Several fast dissolving dosage forms are hygroscopic and cannot maintain physical integrity under normal condition from humidity which calls for specialized product packaging [10].
1.2.4 Mouth feel
Mouth feel is critical, and patients should receive a product that feels pleasant. Any large particles from the disintegrating tablet that are insoluble or slowly soluble in saliva would lead to an unpleasant gritty feeling. This can be overcome by keeping the majority of the particles below the detectable size limit. In some cases, certain flavors can imbibe an improved mouth feel perception, resulting in a product that is perceived as being less gritty, even if the only change is the flavor. Effervescence can be added to aid disintegration and improve mouth feel by reducing the dryness of a product [11, 12].
Thin film drug delivery is a process of delivering drugs to the systemic circulation via a thin film that dissolves when in contact with liquid, often referred to as a dissolving film or strip. Thin film drug delivery has emerged as an advanced alternative to the traditional tablets, capsules and liquids often associated with prescription and OTC medications. Similar in size, shape and thickness to a postage stamp, thin film strips are typically designed for oral administration, with the user placing the strip on or under the tongue or along the inside of the cheek. As the strip dissolves, the drug can enter the blood stream enterically, ducally or sublingually.
The first commercial non-drug product to use thin films was the Listerine PocketPaks breath freshening strips. Since then, thin film products for other breath fresheners, as well as a number of cold, cough, flu and anti-snoring medications, have entered the marketplace. There are currently several projects in development that will deliver prescription drugs utilizing the thin film dosage form [13].
The design of thin film, often referred to as Pharm Film, as an oral drug delivery technology offers several advantages over other modes of drug delivery, such as ingestible tablets, chewable tablets, orally dissolving tablets, softgels, liquids or inhalants[14].
The sublingual and buccal delivery of a drug via thin film has the potential to improve the onset of action, lower the dosing, and enhance the efficacy and safety profile of the medicament.
All tablet dosage forms, softgels and liquid formulations primarily enter the blood stream via the gastrointestinal tract, which subjects the drug to degradation from stomach acid, bile, digestive enzymes and other first pass effects. As a result, such formulations often require higher doses and generally have a delayed onset of action.
Conversely, buccal and sublingual thin film drug delivery can avoid these issues and yield quicker onsets of action at lower doses.
Thin film is more stable, durable and quicker dissolving than other conventional dosage forms.
Thin film enables improved dosing accuracy relative to liquid formulations since every strip is manufactured to contain a precise amount of the drug.
Thin film not only ensures more accurate administration of drugs but also can improve compliance due to the intuitive nature of the dosage form and its inherent ease of administration. These properties are especially beneficial for pediatric, geriatric and neurodegenerative disease patients where proper and complete dosing can be difficult.
Thin film’s ability to dissolve rapidly without the need for water provides an alternative to patients with swallowing disorders and to patients suffering from nausea, such as those patients receiving chemotherapy.
Thin film drug delivery has the potential to allow the development of sensitive drug targets that may otherwise not be possible in tablet or liquid formulations.
From a commercial perspective thin film drug delivery technology offers an opportunity to extend revenue lifecycles for pharmaceutical companies whose drug patent is expiring and will soon be vulnerable to generic competition.
2.3.1 Taste masking
An important aspect of thin film drug delivery technology is the masking of the often bitter and poor taste of drug formulations[14].One method of taste-masking is encapsulation, the coating of drug particles with a polymeric covering sufficient to mask the taste of the drug particle while maintaining the ability to release the drug for absorption. Encapsulation is an efficient method for combining a high ratio of drug-to-non-drug elements in the taste-masked particle. Another method is the use of an ion exchange resin to bind the drug, forming a resinate that is less bitter than the drug alone. Shivang Chaudhary,final year M.S.Pharm student of Indian NAtional Institute of Pharmaceutical Education & Research (NIPER) has formulated Taste masked Quick melting oral strip(QMOS) for quick onset of erection, in which they got success in bitter taste masking of sildenfil citrate via its inclusion complexation within B-Cyclodextrin by simple kneading method.
2.3.2 Drug content uniformity
Drug content uniformity is a requirement for all dosage forms, particularly those containing low dose highly potent drugs. To uniquely meet this requirement, thin film formulations contain uniform dispersions of drug throughout the whole manufacturing process[15].Since this criteria is essential for the quality of the thin film and final pharmaceutical dosage form, the use of Laser Scanning Confocal Microscopy (LSCM) was recommended to follow the manufacturing process[16].
2.3.3 Avoiding drug degradation
Sensitive drugs may degrade over time in an aqueous environment. Thin film formulations must ensure that the integrity of the drug remains constant over time [17]. To overcome these challenges, developers of thin film have created highly specialized unique and often proprietary processes to deliver drugs on thin film [18].
Pharmaceutical companies and consumers alike have embraced OTFs as a practical and accepted alternative to traditional OTC medicine forms such as liquids, tablets, and capsules. OTFs offer fast, accurate dosing in a safe, efficacious format that is convenient and portable, without the need for water or measuring devices [19]. OTFs are typically the size of a postage stamp and disintegrate on a patient’s tongue in a matter of seconds for the rapid release of one or more APIs. The formulation of dissolvable films is customarily facilitated through aqueous polymer matrices that span a wide molecular weight (MW) range, thereby providing flexibility to achieve certain physical properties. With the selection of appropriate polymer excipients, these properties can be tailored to meet specific API-loading needs and dissolution rates.
To date, the commercial launch of OTFs is primarily in OTC products addressing therapeutic categories such as cough/cold, sore throat, and antacid/gas relief as well as a number of nutritional supplement applications [19].
In compliance with the appropriate monographs, current products deliver a specified API dose that is immediately released and ingested. Some drug forms are more easily used in OTFs than others (soluble versus non soluble), but we can expect API concentrations to increase as new OTF formulations are developed.
The capabilities of the base technology to create dissolvable films continue to evolve. For example, a common misconception of the OTF format is that it is limited with regard to the loading capacity of APIs. Some researchers reference a limit of 30 mg of API content as the maximum concentration. A more accurate statement would be that OTFs have the capability to load APIs up to 50% of the unit dose mass, as demonstrated by Novartis Consumer Health’s Gas-X thin film, which contains 62.5 mg of simethicone per dose [20].
Some drug substances may be absorbed more rapidly through the oral mucosal and esophageal tissues via OTF formats during ingestion. Because the drug enters directly into the bloodstream and avoids hepatic first-pass metabolism, bioavailability may be improved, and the drug can be administered in smaller doses. Smaller doses translate to fewer side effects and potentially improved patient compliance. Oral mucosal delivery via OTFs could become a preferential delivery method for therapies in which rapid absorption is desired, including those used to manage pain, allergies, sleep difficulties, and central nervous system disorders.
Functional film properties controlled during manufacturing
OTF formats can be considered for any therapeutic category in which an oral solid, liquid, or ODT format is currently offered. Ideal applications are those that use drug compounds that are potent and possess a narrow therapeutic range [21]. In addition, OTFs are proven to be a more beneficial platform for compromised populations such as children or the elderly where a quick, well-tolerated platform aids administration [22].
From a strategic standpoint, a group of therapeutic categories stand out as leading applications for the OTF format to expand beyond commercial OTC products on the market today (see sidebar, “Strategic therapeutic categories for oral thin films”). Development of a branded prescription OTF product for smoking cessation would set a precedent for the format, much like the launch of transdermal drug delivery patches for smoking cessation did in the 1990s.
Strategic therapeutic categories for oral thin films
The use of thin-film strips is of growing interest in the pharmaceutical sector following the success of Listerine PocketPaks® in the United States. Thin-film strip technology uses a range of water-soluble polymers and is reported to be able to incorporate watersoluble, insoluble, or taste-masked ingredients. The film is manufactured as a continuous sheet and then cut into individual doses prior to packing. The major limitations to this technology are the relatively low doses that can be accommodated (approximately 30 mg) and its moisture sensitivity thus requiring specific unit-dose packaging to protect the product and ensure shelf life. Thin-film technology has primarily been used in over the- counter (OTC) products.
TCI’s report also details the technology programs of 25 companies active in the development of Orally-Disintegrating Tablet technologies and 17 active in the development of Oral Film technologies. Technology Catalysts forecasts the market for drug products in oral thin film formulations to be valued at $500 million in 2007 and could reach $2 billion by 2010.
The first oral strip was developed by Pfizer (New York) as a mouth freshening product (“Listerine” pocket packs). “Chloraseptic Relief Strips” (distributed by Prestige Brands, Irvington, NY), Theraflu Thin Strips treat the most common symptoms of a cold in adults and children 12 and older and will be available in two cherry-flavoured treatment options: Long Acting Cough that quiets coughs for up to eight hours, and Multi-Symptom that, as well as tackling coughs, is said to provide temporary relief from a runny nose and sneezing, and soothes itchy, watery eyes and throat. Both will cost approximately $5.49 for a 12-strip pack.
Meanwhile, Triaminic Thin Strips, for children ages 6-12, will also be available in two treatment options: Long Acting Cough that quiets coughs for up to eight hours, in cherry flavor, and Cough & Runny Nose, in grape flavour. They will cost approximately $5.99 for a 16-strip pack, according to Novartis.
A variety of polymers are available for preparation of OS. The polymers can be used alone or in combination to obtain the desired strip properties. The film obtained should be tough enough so that there won’t be any damage while handling or during transportation. The robustness of the strip depends on the type of polymer and the amount in the formulation [23].
On the other hand, fast dissolving strip dosage formshould have the property to disintegrate in seconds when placed in mouth and deliver the drug to the oral cavity instantaneously. A list of polymers and their properties are given in Table 5 [24-30]. As the strip forming polymer (which forms the platform for the OS) is the most essential and major component of the OS, at least 45%w/w of polymer should generally be present based on the total weight of dry OS [31]. Of the various polymers available, pullulan, gelatin and hypromellose are most commonly used for preparation of OS. Pullulan is a natural polymer obtained from non-animal origin and does not require chemical modification. This polymer provides highly clear and homogenous films. It has low oxygen permeability and low water content which makes it most suitable for production of OS [32]. Many times, mixtures of polymers are used to improve hydrophilicity, flexibility, mouth-feel and solubility characteristics of OS.
Polyvinyl pyrrolidone films are brittle in nature and therefore copovidone is mixed with poly vinyl pyrrolidone for preparation of flexible fast disintegrating strips [33]. Combination of microcrystalline cellulose and maltodextrin has been used to formulate OS of piroxicam made by hot melt extrusion technique. In this case, microcrystalline cellulose is used to render the film non-sticky and smooth [34]. Microcrystalline cellulose was also used to decrease the disintegration time and improve the dissolution of drug from the OS [35].
Property of polymer
Various polymers can be employed to modulate the disintegration property of the oral strip. This is especially used in case of slowly disintegrable oral bioadhesive strips or patches that need to be retained in intact form for longer duration in the oral cavity. The bioadhesive polymer used in such formulations imparts the adhesive property to the strip such that it adheres to buccalmucosa to deliver the drug for prolonged period. Bioadhesive polymer should ideally adhere quickly to the buccal mucosa and should have sufficient mechanical strength. Polymers used for OS should have good shelf life and they should not aid in causing secondary infections in the oral mucosa or dental regions. It would be ideal to have a polymer that would have local enzyme inhibition action along with penetration enhancing property. The details of properties of bioadhesive or mucoadhesive polymers and their applications are discussed elsewhere [36-43]. Mucoadhesive polymers include polycarbophil, cellulose derivatives like hydroxypropyl methylcellulose, poly(acrylic acid) derivatives, sodium carboxymethyl cellulose, hydroxylethyl cellulose, hyaluronic acid, xanthan gum, locust bean gum, guar gum, carrageenan, sodiumalginate, chitosan, poly(ethylene oxide), poly (ortho esters), poly (hydroxyl butyrate), poly(cyano acrylates), polyphosphazenes, poly (vinyl alcohol) etc.
Second generation mucoadhesive polymers include thiolated polymers. They are multifunctional polymers consisting of hydrophilic macromolecules having free thiol groups on the polymer backbone. The polymer forms disulfide bonds with cysteine-rich subdomains of mucus glycoproteins. Corium International has developed a new class of adhesive hydrogels (Corplex„¢) [44].
There are a number of marketed products available that are based on mucoadhesion phenomena. Oramoist® is a Timed Release oral disk that adheres to the roof of the mouth and has a moisturizing effect for about 4 h [44]. It is recommended for dry mouth syndrome (xerostomia). Compeed® is another formulation that is intended to treat cold sore [46].
Polymer: Hydoxy propyl methyl cellulose (HPMC)
Synonym: Methocel, Metolose, Benecel (Hypromellose)
Description: It is a odorless, tasteless and white or creamy white fibrous or granular powder
Molecular weight: 10,000-1,500,000
Solubility: Soluble in cold water,forming a viscous colloidal solution, insoluble in chloroform, ethanol
–
Polymer: Hydroxy propyl cellulose
Synonym: Hydroxyl propyl ether, hyprolose, Klucel, Nisso HPC.
Description: It is a white to slightly yellow colored, odorless and tasteless powder. It is stable material
Molecular weight: 50,000-1,250,000
Solubility: It is freely soluble in water below 38 °C forming a smooth, clear, colloidal solution. Hydroxypropyl cellulose is soluble in many cold and hot polar organic solvents such as absolute ethanol, methanol, isopropyl alcohol and propylene glycol
–
Polymer: Starch and modified starch
Synonym: Amido, amylum, PharmGel, Fluftex W, Instant pure-Cote, Melogel etc.
Description: It is an odorless, tasteless, fine, white powder.
Molecular weight: 50,000-160,000
Solubility: It is insoluble in cold water and ethanol. It swells in water by about 5 to 10% at 37 °C
–
Polymer: Pullulan
Synonym: Pullulane, 1, 6 α linked maltotriose
Description: It is available as white, odorless tasteless, stable powder
Molecular weight: 8000-2,000,000
Solubility: It is soluble in hot as well as cold water
–
Polymer: Pectin
Synonym: Citrus pectin, Methopectin, pectin, pectinic acid
Description: It occurs as a yellowishwhite, odorless powder with mucilaginous taste.
Molecular weight: 30,000-100,000
Solubility: It is soluble in water but insoluble in most of the organic solvents.
–
Polymer: Gelatin
Synonym: Byco, cryogel, Instagel, Solugel
Description: It occurs as light amber to faintly yellow colored, vitreous, brittle solid. It is ordorless, tasteless.
Molecular weight: 15,000-250,000
Solubility: Soluble in glycerin, acid and alkali. Swells in water and softens. It is soluble in hot water
–
Polymer: Carboxy methyl cellulose
Synonym: Akulell, Blanose, Aquasorh
Description: It is white, odorless powder
Molecular weight: 90,000-700,000
Solubility: It is easily dispersed in water to form a clear or colloidal solution
Plasticizer is a vital ingredient of the OS formulation. It helps to improve the flexibility of the strip and reduces the brittleness of the strip. Plasticizer significantly improves the strip properties by reducing the glass transition temperature of the polymer. The selection of plasticizer will depend upon its compatibility with the polymer and also the type of solvent employed in the casting of strip. The flow of polymer will get better with the use of plasticizer and enhances the strength of the polymer [47, 48].
Glycerol, Propylene glycol, low molecular weight polyethylene glycols, phthalate derivatives like dimethyl, diethyl and dibutyl phthalate, Citrate derivatives such as tributyl, triethyl, acetyl citrate, triacetin and castor oil are some of the commonly used plasticizer excipients. Typically the plasticizers are used in the concentration of 0-20%w/w of dry polymer weight [49-57]. However inappropriate use of plasticizer may lead to film cracking, splitting and peeling of the strip [58-60]. It is also reported that the use of certain plasticizers may also affect the absorption rate of the drug [61].
The active substance is may be from any class of pharmaceutically active substances that can be administered orally or through the buccal mucosa, respectively. The OS technology has the potential for delivery of variety of APIs. However since the size of the dosage form has limitation, high dose molecules are difficult to be incorporated in OS. Generally 5%w/w to 30%w/w of active pharmaceutical ingredients can be incorporated in the OS [62]. Multivitamins up to 10%w/w of dry film weight was incorporated in the OS with dissolution time of less than 60 s [32].
APIs can also be added as milled, micronized or in the form of nanocrystals or particles depending upon the ultimate release profile desired. It is always useful to have micronized API which will improve the texture of the film and also for better dissolution anduniformity in the OS [63].
Some of the examples of suitable drug molecule that can be incorporated in the OS are listed in table-6.
Sweeteners have become the important part of the food products as well as pharmaceutical products intended to be disintegrated or dissolved in the oral cavity.
Natural sweeteners as well as artificial sweeteners are used to improve the palatability of the mouth dissolving formulations. Sweetening agent such as Sugar, dextrose, lactose, mannitol, sucrose, xylitol, malitol, acesulfame potassium, talin, glycyrrhizin, sucralose, aspartame, saccharin etc.
The classical source of sweetener is sucrose (derived from cane or beet in the form of liquid or dry state), dextrose, fructose, glucose, liquid glucose and maltose. The sweetness of fructose is perceived rapidly in the mouth as compared to sucrose and dextrose. Fructose is sweeter than sorbitol and mannitol and thus used widely as a sweetener.
The artificial sweeteners have gained more popularity in food and pharmaceutical preparations. Saccharin,cyclamate and aspartame are the first generation of the artificial sweeteners followed by acesulfame-K, sucralose, alitame and neotame which fall under the second generation artificial sweeteners. Acesulfame-K and sucralose have more than 200 and 600 time sweetness. Neotame and alitame have more than 2000 and 8000 time sweetening power as compared to sucrose. Rebiana which is a herbal sweetener, derived from plant Stevia rebaudiana (South American plant) has more than 200-300 time sweetness [64].The flavor quality of these artificial sweeteners is different than the natural sweeteners and may not be acceptable to the patients who are accustomed to the natural sugars. The amalgamation of sweeteners may lead to synergismand improvement in the taste of the formulations [65]. Aspartame was used for the preparation of oral strips of valdecoxib [66]. For the oral strip of piroxicam, maltodextrin was employed as sweetening agent [67]. Generally sweeteners are used in the concentration of 3 to 6 %w/w either alone or in combination [68].
Perception for the flavors changes from individual to individual depending upon the ethnicity and liking. The selection of flavor is also dependant on the type of drug to be incorporated in the formulation. For example, mint flavor is generally added in products used for gastric related ailments like indigestion. The acceptance of the oral disintegrating or dissolving formulation by an individual by and large depends on the initial flavor quality which is observed in first few seconds after the product has been consumed and the after taste of the formulation which lasts for at least about 10 min [69].
Flavoring agents can be selected from synthetic flavor oils, oleo resins, extract derived from various parts of the plants like leaves, fruits and flowers. Flavors can be used alone or in the combination. Peppermint oil, cinnamon oil, spearmint oil, oil of nutmeg are examples of flavor oils while vanilla, cocoa, coffee, chocolate and citrus are fruity flavors. Apple, raspberry, cherry, pineapple are few examples of fruit essence type. The amount of flavor needed to mask
the taste depends on the flavor type and its strength. Preferably up to 10%w/w flavors are added in the OS formulations. Cooling agents like monomethyl succinate can be added to improve the flavor strength and to enhance the mouth-feel effect of the product. Other cooling agents likeWS3, WS23 and Utracoll II can also be used in conjunction with flavors [68, 70].
Coloring agents may include FD & C coloring agents, natural coloring agents, and natural juice concentrates, pigments such as titanium oxide, silicon dioxide and zinc oxide. (not exceeding concentration levels of 1%w/w) in OS .when some of the formulation ingredients or drugs are present in insoluble or suspension form [71,72].
The stabilizing and thickening agents are employed to improve the viscosity and consistency of dispersion or solution of the strip preparation solution or suspension before casting. Natural gums like xanthan gum, locust bean gum, carragenan and cellulosic derivatives can be used in the concentration up to 5%w/w as thickening agents and stabilizing agents [68]. Other ingredients such as surfactants and emulsifying agents are also added in small amount to improve the strip properties.
The purpose of using saliva stimulating agents is to increase the rate of production of saliva that would aid in the faster disintegration of the rapid dissolving strip formulations. Generally acids which are used in the preparation of food can be utilized as salivary stimulants. Citric acid, malic acid, lactic acid, ascorbic acid and tartaric acid are the few examples of salivary stimulants, citric acid being the most preferred amongst them.
These agents are used alone or in combination between 2 to 6%w/w of weight of the strip. Other OS ingredients such as sweeteners also act as salivary stimulants. Food grade sugars as well as synthetic sugars are useful salivary stimulants along with acidulents. Glucose, fructose, xylose, maltose, lactose are few examples of such sweeteners [73]. The resting salivary flow rate was 0.34 ml/min .but citric acid is capable to increase the salivary flow rate up to 1.68ml/min [73].
One (or a combination) of the following processes may be used to manufacture the oral films [74].
The oral film is preferably formulated using the solvent-casting method, whereby the water-soluble ingredients are dissolved to form a clear viscous solution. The API and other agents are dissolved in smaller amounts of the solution, and combined with the bulk. This mixture is then added to the aqueous viscous solution. The entrapped air is removed by vacuum. The resulting solution is cast as a film and allowed to dry, which is then cut into pieces of the desired size. Water-soluble hydrocolloids used to prepare films are: hydroxypropylmethyl cellulose (HPMC), hydroxypropyl cellulose (HPC), pullulan, sodium alginate, pectin and carboxymethyl cellulose (CMC) [75].
Hot melt extrusion (HME) is commonly used to prepare granules, sustained-release tablets, transderm
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