April 27, 2011
by Charlotte Dieroff
Orally disintegrating tablets (ODTs) are a popular delivery form found in many prescription, over-the-counter (OTC) medicines and dietary supplements. These technologies are often referred to as melt-in-mouth, rapimelt, rapid disintegrating, orodispersible, quick dissolving or porous tablets, not to be confused with chewable tablets that require chewing and swallowing.
FDAs Center for Drug Evaluation and Research (CDER) defines an ODT as a solid dosage form containing medicinal substances, which disintegrates rapidly, usually within a matter of seconds, when placed upon the tongue.1 Examples of well-known ODTs are Jr. Tylenol Meltaways, Benedryl Fastmelts and Claritin Ready Tabs.
Because ODTs dissolve in the mouth with saliva, they release the active drugs in pregastric, gastric and postgastric phases of the gastrointestinal (GI) system. On the contrary, conventional tablets must be swallowed with water for dissolution, released, and absorbed in the stomach and postgastric sites of the GI system.
Reasons to Use ODTs
ODTs offer ease of use and increased overall patient compliance. ODTs offer a value-added alternative for patients who cannot swallow conventional hard tablets or gel caps. These patient groups include those with dysphasia, the elderly, stroke victims and bedridden patients. Some patients also refuse to swallow conventional tablets such as uncooperative pediatrics, geriatrics and psychiatric patients. An additional, but often overlooked, benefit to ODTs is the convenience factor for patients who do not have readily available access to water due to travel or as part of our modern on the go lifestyles. These are all reasons that often lead to poor compliance with conventional tablets.
Recent market studies indicate more than half of the patient population prefers ODTs to other dosage forms,2 and most consumers would ask their doctors for ODTs (70 percent), purchase ODTs (70 percent) or prefer ODTs to regular tablets or liquids (greater than 80 percent).3
Common Types of ODTs
The two main forms of ODTs are freeze-dried formulations and loosely compressed tablets. Some industry members define a third delivery form as oral thin-film strip products such as Chloraseptic Relief Strips and Listerine Pocket Paks; however, as these formats are not tablets, they are not discussed in this article.
The most successful commercial ODT freeze drying manufacturing technology is the Zydis process, which was the first patented ODT technology to market. This tablet dissolves in the mouth within seconds after placement on the tongue. A Zydis tablet is produced by preparing an aqueous drug solution or suspension in bulk, dosing it into preformed blister packs and then cryogenically freezing it to ensure development of porous material. Next, the blister packs are moved to freeze dryers where most of the water is removed from the tablets. Last, the blister packs are heat-sealed to ensure stability.
This process results in a highly porous structure, which increases quick dissolution. Advantages include rapid dissolution, self-preservation from microbial growth and increased bioavailability. The main drawback is higher cost, due in part to a more time-consuming manufacturing process. Additionally, these tablets can have poor stability at high temperature and humidity conditions. Furthermore, these tablets are more fragile than others and must be packaged in special blister packs to prevent mechanical and moisture damage. Other technologies using freeze-drying techniques are Lyoc and QuickSolv.
Compressed tablet systems are based on conventional tableting technology and are the easiest way to manufacture ODTs. Using conventional equipment, ingredients and a limited amount of processing steps makes this system a cost-effective manufacturing method. In this process, the active drug, diluents, binders and disintegrants are finely milled, blended and then compressed into tablets.
Some advantages of direct compression are higher dose delivery of active compounds as well as mechanically stronger, more robust tablets. A disadvantage is relatively slower dissolution rates when compared to freeze-dried tablets. Some well-known technologies using direct compression are OraSolv, DuraSolv and WOWTAB.
Overcoming Formulation Challenges
Brent Fairbrother, associate food scientist at The International Food Network (IFN) has experience in direct compression ODT formulation. He explained that masking the inherent bitter flavor of most active ingredients is a large challenge when formulating this type of ODT. Fairbrother described how sugar and sugar alternatives are inexpensive ingredients that add sweetness to dissipate unwanted bitter notes. He also shared an additional way to get around bitter actives is to encapsulate the active itself.
Another ODT formulation challenge is tablet friability (tendency of tablets to break when mechanically agitated). ODTs typically require less compression force, compared to conventional tablet forms, to allow for fast disintegration times. The softer tablet allows for easy moisture penetration, thus aiding in the tablet break up during consumption. To protect the softer more friable tablet, ODTs are commonly packaged in rigid blister packs.
Ingredient technologies such as super disintigrants are also used by formulators to help combat this friability issue, allowing for the ultra-fast disintegration of harder tablets. Super disintigrants such as sodium starch glycolate, crospovidone and croscarmellose sodium are more hydrophilic. These ingredients aid in the water uptake of the tablet even when little moisture is present, allowing for a disruptive change in the tablet. ODTs containing these super disintigrants can be compressed harder because of the increased moisture uptake of its ingredients.
ODTs in the Future
Historically, ODTs have been limited in application to small molecular weight pharmaceutical actives. As technology is changing, ODTs may be able to carry larger molecular weight proteins and peptides, which have limited bioavailability when administered through conventional tablets as low gastric pH causes rapid degradation of the drug. Currently, these classes of molecules have been developed as injectable drugs, but advances in ODT technology may allow for oral administration in the future.
Charlotte Dieroff is a product developer at the International Food Network (IFN) and holds a bachelors of science in Food Science from Cornell University and an masters of business administration from Xavier University. Her background includes developing frozen desserts, weight-loss and dry-mix beverages. Since 1987, IFN has provided new product development services to the supplement, nutritional products, and food and beverage industries. Based in Ithaca, NY, with additional technical centers in Naples, FL, and Reading, England, the firm employees more than 50 degreed scientists, technologists and culinologists. To contact IFN, call 866-778-5129
2. Deepak K. Orally disintegrating tablets. 2004 Tablets and Capsules 7: 30-35.
3. Brown D. Orally disintegrating tablets: Taste over speed. 2001. Drug Delivery Technology,3(6); 58-61.
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