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can be promoted as improving the consumer's experience. Just look at the evidence: A surge of effervescent prod- ucts is showing up on store shelves, online, and through direct marketers. The new products run the gamut: phar- maceuticals, dietary supplements, foods, and cleansers. Why use effervescent technology? For consumers, effervescent products provide a multi- sensory in-use experience. They watch the fizzing action, hear the bubbling, and receive a drug product or dietary supplement that tastes good. Experienced formulators know that the more senses a product stimulates, the more likely it is to delight consumers. Since effervescent products are almost always dis- solved before they're ingested, they allow active ingredi- ents to be solubilized or dispersed before they reach the gut. That can speed adsorption and bioavailability. Pre- dissolution also benefits patients who have trouble swal- lowing conventional tablets or capsules. In addition, effervescent bases provide an excellent environment for moisture-sensitive active ingredients. That's because the bases are anhydrous, which practically eliminates the risk of hydrolysis, a common cause of degradation. This is discussed in more detail below. Product forms Most effervescent products are tablets, and many of them sell under well-known brands, including Alka- Seltzer, Airborne, Nuun, Berocca, Blowfish, Liftoff, Best Defense, Polident, and Efferdent. Most are packaged in foil or in tubes. If they're powders or granules, the prod- ucts are packaged in stick packs and sachets. Examples of these include Emergen-C, Efferdent Crystals, and Fresh Guard. Effervescent chemistry The chemistry that underlies the appeal of efferves- cent products is quite simple (Figure 1). An acid is used to neutralize a carbonate salt. That causes a reaction that produces carbon dioxide (CO 2 ) gas, the salt of the acid, and water. It's the CO 2 gas—the fizzing—that makes effervescent products appeal to our senses. A few important points about the reaction may not be obvious. First, water is needed. Without water, neither the acid nor the carbonate can dissociate, and without dissociation, no effervescent reaction can occur. Once the reaction does start, the stoichiometry dictates that it generates more water. In other words, once started, the acid and carbonate will continue to dissociate and the effervescent reaction will self-propagate. This means that effervescent products are inherently unstable and must be carefully formulated, manufactured, and packaged. Doing this entails keeping the raw materials virtually anhydrous and warehoused so they remain dry. Likewise, the manufacturing environment must be highly dehumid- ified to prevent the products from picking up unwanted moisture. And the packaging must include a moisture- barrier film, usually with an aluminum foil layer. The other option is to place the product in a tube that con- tains a desiccant to protect it from ambient humidity dur- ing shipping, storage, and use. Any lapse that allows moisture infiltration can cause the product to give off CO 2 and water before it reaches the consumer. If that happens, the product will become mushy and the foil package will look like a puffy pillow. Flexible foil and aluminum or plastic tubes are the two most common packages for effervescent tablets because of the moisture barrier they provide. Figure 1 Effervescent reaction Acid + carbonate salt → CO 2 ↑ + Acid salt + H 2 0 Example Citric acid + 3NaHCO3 → 3CO 2 ↑ + Na 3 Citrate + 3H 2 0 12 July 2016 Tablets & Capsules