MOUTH DISSOLVING TABLET: A OVERVIEW

About Authors:
Ashish Kumar Garg*, M.M. Gupta
Department of Pharmaceutics, Jaipur College of Pharmacy,
Jaipur, Rajasthan
*ashish1pharma@gmail.com

Abstract
Conventional dosage forms like tablets and capsules are now days facing the problems like dysphagia, resulting in the high incidence of non compliance and making the therapy ineffective. To obviate the problems associated with conventional dosage forms, mouth dissolving tablets have been developed having good hardness, dose uniformity, easy administration and serves as the first choice of dosage form for paediatrics, geriatrics and traveling patients. The MDTs were developed with an aim of having sufficient hardness, integrity and faster disintegration without water. Fast dissolving Tablets are disintegrating and/or dissolve rapidly in the saliva without the need for water. Some tablets are designed to dissolve in saliva remarkably fast, within a few seconds, and are true fast-dissolving tablets. Others contain agents to enhance the rate of tablet disintegration in the oral cavity, and are more appropriately termed fast-disintegrating tablets, as they may take up to a minute to completely disintegrate. This tablet format is designed to allow administration of an oral solid dose form in the absence of water or fluid intake. Such tablets readily dissolve or disintegrate in the saliva generally within <60 seconds.


Reference Id: PHARMATUTOR-ART-1567

INTRODUCTION
Despite of tremendous innovations in drug delivery, the oral route remains the preferred route for administration of therapeutic agents because of accurate dosage, low cost therapy, self medication, non invasive method and ease of administration leading to high level of patient compliance[1]. However, traditional tablets and capsules administered with a glass of water may be inconvenient or impractical for some geriatric patients because of changes in various physiological and neurological conditions associated with aging including difficulty in swallowing/dysphagia, hand tremors, deterioration in their eyesight, hearing, memory, risk of choking in addition to change in taste and smell. Solid dosage forms also present significant administration challenges in other patient groups, such as children, mentally challenged, bed ridden and uncooperative patients. Pediatric patients may suffer from ingestion problems as a result of underdeveloped muscular and nervous control. Moreover, patients traveling with little or no access to water, limit utility of orally administered conventional tablets or capsules.

Therefore, to cater the needs of such patients, recent advancements in technology have resulted in development of viable dosage alternatives popularly known as orally disintegrating tablets (ODTs)[1,2].During the past decade, the FDT (fast dissolving tablet) technology, which makes tablets dissolve or disintegrate in the mouth without additional water intake, has drawn a great deal of attention.The technology is also referred to as fast disintegrating tablet, fast dispersing tablet, rapid dissolve tablet, rapid melt tablet, quick disintegrating tablet, and orally disintegrating tablet. The FDT formulation is defined by the Food and Drug Administration (FDA) as ‘‘a solid dosage form containing medicinal substances which disintegrates rapidly, usually within a matter of seconds, when placed upon the tongue’’. The tablets disintegrate into smaller granules or melt inthe mouth from a hard solid structure to a gel like structure, allowing easy swallowing by the patients. The disintegration time for those tablets varies from a few seconds to more than a minute[2,3].

FDT is a desirable dosage form for patients with problems swallowing tablets or other solid dosage forms. It has advantages over oral solutions including better stability, more accurate dosing, and lower volume and weight. The dosage form can be swallowed as a soft paste or liquid, and suffocation is avoided because there is no physical obstruction when swallowed. Since the tablets disintegrate in the mouth, drugs can be absorbed in the buccal, pharyngeal, and gastric regions. Thus, rapid drug therapy intervention and increased bioavailability of drugs might be possible.Because pre-gastric drug absorption avoids first pass metabolism, the drug dose can be reduced if a significant amount of the drug is lost through the hepatic metabolism.

Administration of FDTs is different from conventional tablets, and the FDTs should have several unique properties to accommodate the rapid disintegration time. They should dissolve or disintegrate in the mouth without water or with a very small amount of water as the disintegration fluid is the patient’s saliva. The disintegrated tablet should become a soft paste or liquid suspension, which provides good mouth feel and enables smooth swallowing. ‘‘Fast dissolution’’ or ‘‘fast disintegration’’ typically requires dissolution or disintegration of a tablet withinoneminute.[1,2]

Significance of ODTs [4,5]
ODTs offer dual advantages of solid dosage forms and liquid dosage forms along with special

Features which include:
· Accurate dosing: Being unit solid dosage forms, provide luxury of accurate dosing, easy portability and manufacturing, good physical and chemical stability and an ideal alternative for pediatric and geriatric patients.
· Enhanced bioavailability: Bioavailability of drugs is enhanced due to absorption from mouth , pharynx and esophagus.
· Rapid action: Fast onset of therapeutic action as tablet gets disintegrated rapidly along with quick dissolution and absorption in oral cavity.
· Patient compliance: No need of water to swallow the dosage form. Hence, it is convenient for patients who are traveling and do not have immediate access to water.
· Ease of administration: Convenient to administer specially for geriatric, pediatric, mentally disabled and bed ridden patients who have difficulty in swallowing.
· Obstruction free: No risk of suffocation in airways due to physical obstruction when swallowed, thus providing improved safety and compliance.
· Enhanced palatability: Good mouth feels, especially for pediatric patients as taste masking technique is used to avoid the bitter taste of drug.
· Simple packaging: No specific packaging required. It can be packaged in push through blisters.
· Business Avenue: Provide new business opportunities in the form of product differentiation, line extension, uniqueness and life cycle management.
· Cost effective: Conventional processing and packaging equipments allow the manufacturing of tablets at low cost.

Ideal Properties of MDTs[4]

They should –
*  Not require water to swallow, but it should dissolve or disintegrate in the mouth in matter of seconds.
*  Be compatible with taste masking.
*  Be portable without fragility concern.
*  Have a pleasant mouth feel.
*  Leave minimum or no residue in the mouth after oral administration.
*  Exhibit low sensitive to environmental condition as temperature and humidity.
*  Allow the manufacture of the tablet using conventional processing and packaging equipments at low cost.

Challenges in formulating Fast dissolving tablets:[5,19]

Palatability
As most drugs are unpalatable, FDTs usually contain the medicament in a taste-masked form. Upon administration, it disintegrate or dissolve in patient’s oral cavity, thus releasing the active ingredients which come in contact with the taste buds. Hence, taste-masking of the drugs becomes critical to patient compliance .

Mechanical strength
In order to allow FDTs to disintegrate in the oral cavity, they are made of either very porous and soft-molded matrices or compressed into tablets with very low compression force, which makes the  tablets friable and/or brittle, difficult to handle, andoften requiring specialized peel-off blister packing that may add to the cost. Only Wow tab and durasolv technologies can produce tablets that are sufficiently hard and durable to allow them to be packaged in multi-dose bottles.

Hygroscopicity
Several orally disintegrating dosage forms are hygroscopic and cannot maintain physical integrity under normal conditions of temperature and humidity. Hence, they need protection from humidity which calls for specialized product packaging.

Amount of drug
The application of technologies used for FDTs is limited by the amount of drug that can be incorporated into each unit dose. For lyophilized dosage forms, the drug dose must be less than 400 mg for insoluble drugs and 60 mg for soluble drugs. This parameter is particularly challenging when formulating a fast-dissolving oral films or wafers.

Aqueous solubility
Water-soluble drugs pose various formulation challenges because they form eutectic mixtures, which result in freezing-point depression and the formation of a glassy solid that may collapse upon drying because of loss of supporting structure during the sublimation process. Such collapse sometimes can be prevented by using various matrix-forming excipients such as mannitol that can induce crystallinity and hence, impart rigidity to the amorphous composite.

Size of tablet
The ease of administration of a tablet depends on its size. It has been reported that the easiest size of tablet to swallow is 7-8 mm while the easiest size  to handle was one larger than 8 mm. Therefore, the tablet size that is both easy to take and easy to handle is difficult to achieve.

FORMULATION OF MDTs:[5,6,7,8]

Drug:
The ultimate characteristics of a drug for dissolution in the mouth and pre gastric absorption from MDTs include:
*  Free from bitter taste
*  Dose lower than 20 mg
*  Small to Moderate molecular weight
*  Good solubility in saliva
*  Ability to permeate through oral mucosal tissue

Bulking materials:
Bulking materials are significant in the formulation of fast-melting tablets. The material contributes functions of a diluent, filler and cost reducer. Bulking agents improve the textural characteristics that in turn enhance the disintegration in the mouth, besides; adding bulk also reduces the concentration of the active in the composition. The recommended bulking agents for this delivery system should be more sugar-based such as mannitol, polydextrose, lactitol, DCL (direct compressible lactose) and starch hydrolystate for higher aqueous solubility and good sensory perception. Mannitol in particular has high aqueous solubility and good sensory perception. Bulking agents are added in the range of 10 percent to about 90 percent by weight of the final composition.

Emulsifying agents:
Emulsifying agents are important excipients for formulating fast-melting tablets they aid in rapid disintegration and drug release without chewing, swallowing or drinking water. In addition, incorporating emulsifying agents is useful in stabilizing the immiscible blends and enhancing bioavailability. A wide range of emulsifiers is recommended for fast-tablet formulation, including alkyl sulfates, propylene glycol esters, lecithin, sucrose esters and others. These agents can be incorporated in the range of 0.05 percent to about 15 percent by weight of the final composition.

Lubricants:
Lubricants, though not essential excipients, can further assist in making these tablets more palatable after they disintegrate in the mouth. Lubricants remove grittiness and assist in the drug transport mechanism from the mouth down into the stomach.

Flavours and sweeteners:
Flavours and taste-masking agents make the products more palatable and pleasing for patients. The addition of these ingredients assists in overcoming bitterness and undesirable tastes of some active ingredients. Both natural and synthetic flavours can be used to improve the organoleptic characteristic of fast-melting tablets. Formulators can choose from a wide range of sweeteners including sugar, dextrose and fructose, as well as non-nutritive sweeteners such as aspartame, sodium saccharin, sugar alcohols and sucralose. The addition of sweeteners contributes a pleasant taste as well as bulk to the composition.

Superdisintegrants:
A disintegrant is an excipient, which is added to a tablet or capsule blend to aid in the breakup of the compacted mass when it is put into a fluid environment.

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