Effervescent tablets dissolution

Lozenges These are compressed tablets formulated, without a disintegrant and must be allowed to dissolve in the mouth. They are used for local activity (throat lozenges) or for systemic effect (vitamins). Effervescent tablets These tablets undergo quick dissolution of actives in water due to internal liberation of carbon dioxide. By combining alkali metal carbonates or bicarbonates with tartaric or citric acid, carbon dioxide is liberated when placed in water. 

With regard to compressibility and compactibility, the considerations pertaining to raw materials in effervescent products are similar to the ones that prevail in evaluating raw materials intended for conventional tablets. However, poor compactibility cannot usually be compensated for by the use of binders, as this will prevent a rapid dissolution of the effervescent tablet. Addition of a binder is generally not as critical for the dissolution of effervescent granules or powders. 

Metal stearates, such as magnesium or calcium stearate that serve as lubricants in conventional tablets, are seldom used as intrinsic lubricants in connection with effervescent tablets due to their insolubility in water. Use of stearates results in an undissolved, foamy, soapy-tasting layer on the surface of the cloudy solution. In addition, normal lubricant concentrations of metal stearates make the tablets hydrophobic, which entails a slow dissolution of the effervescent tablet in the water. However, very low concentrations of metal stearates can be used to improve the rate of solution of effervescent tablets as the tablet will remain immersed in the water during dissolution and not float to the surface the way a tablet without metal stearate would. A floating tablet presents a smaller surface area to the water than a tablet immersed in the liquid. 

The use of binders will normally prevent a rapid dissolution of the effervescent tablet. Therefore, many effervescent tablets are formulated without any binder. However, effervescent granules may be formulated with binders since their large surface area, when compared withthat of the conventional or the effervescent tablet, will result in rapid dissolution. An effervescent... 

The disintegration and dissolution times are very important characteristics of effervescent products. A well-formulated effervescent tablet will disintegrate and dissolve within 1-2 min to form a clear solution. Consequently, the residue of undissolved drug must be minimal. The temperature of the water influences the dissolution time. It is, therefore, important to choose a water temperature that is actually used by consumers (e.g., cold tap water). Ph. Eur. includes a general requirement on disintegration time of 5 min in water 15-25°C.t ... 

Tablets may also be prepared with sodium bicarbonate alone since the acid of gastric fluid is sufficient to cause effervescence and disintegration. Sodium bicarbonate is also used in tablet formulations to buffer drug molecules that are weak acids, thereby increasing the rate of tablet dissolution and reducing gastric irritation. ...

Since an effervescent tablet is required to dissolve within 2 min or less in a glass of water (about 100 mL), the solubility of raw materials and their rate of solubility are other significant parameters. The active ingredient must be soluble, water dispersible, or at least solubilized by salt formation during the dissolution in the glass of water. The rest of the excipients, such as additives like sweeteners, coloring agents, flavors, also have to be water soluble. 

The most popular binder for effervescent tablets is polyvinylpyrrolidone (PVP). Types K25 and K30 are preferred for their water solubility and dissolution rate which is an important parameter for the final purpose of effervescent tablets. PVP is effective at low percentage in the formula, starting from 2% and over. It is feasible either for dry or wet granulation. It is soluble in water, alcohols, and hydroalcoholic liquids (18). 

Several researchers had found that the bioavailability of aspirin from effervescence tablet was higher than conventional or enteric-coated tablets (32-34). The reasons for this included the dramatic disintegration rate of the tablets that enabled rapid release of the drug particles for dissolution and the increase in gastric emptying rate. 

Uses Dissolution enhancer for actives in tablets and capsules polishing agent for fi Im-coaled tablets water-soluble lubricant for effervescent tablets Regulatory USP/NF, EP, JPE... 

Fig. 3 Relationship between the dissolution parameter tgo-io of effervescent enteric tablets of levodopa and the amount of sodium bicarbonate formulated in the tablet. The number of strokes was fixed at 5/min and the pH was 7.5. Key ( ) = uncoated tablet (O) = enteric tablet. (From Ref. "l)...

Chemical stability, disintegration rate, dissolution profile, friability, and hardness are the major stability attributes for the tablet dosage form. An unoptimized tablet formulation may become soft or very hard after storage, with altered dissolution profiles, and as a result, its dissolution profile and bioavailability may not be appropriate. If effervescent products are not properly formulated, manufactured, and packaged, the premature acid-base reaction will cause the product s self-destruction. 

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