Effervescent tablet

From Pharmpedia

As per revised definition proposed to US FDA, Effervescent tablet is a tablet intended to be dissolved or dispersed in water before administration.
It generally contains in addition to active ingredients, mixture of acids/acid salts (citric, tartaric, malic acid or any other suitable acid or acid anhydride) and carbonate and hydrogen carbonates (sodium, potassium or any other suitable alkali metal carbonate or hydrogen carbonate) which release carbon dioxide when mixed with water. Occasionally, active ingredient itself could act as the acid or alkali metal compound necessary for effervescent reaction.
Effervescent tablets are uncoated tablets that generally contain acid substances and carbonates or bicarbonates and which react rapidly in the presence of water by releasing carbon dioxide. They are intended to be dissolved or dispersed in water before use.
 

Effervescent mixtures have been known for over 250 years. The famous Rochelle salt (potassium sodium tartrate) dates back to 1731 in conjunction with such a mixture. In the 18th century, effervescent powders as saline cathartics were listed as “Seidlitz powders” in the official compendia.
In the 1930s, the effervescent products gained much importance with the technology of Alka Seltzer. These mixtures have been moderately popular over the years since along with medicinal activity they are attractive dosage form for the patients. Effervescent reactions have been used alternatively preparation of other dosage forms, such as suppositories (for laxative effect), vaginal suppositories (for contraceptive effect) and drug delivery system.