**2. Formulations of orally disintegrating tablets**

ODTs are frequently prepared for immediate release, but they can also be formulated for prolonged or controlled release. Rapid disintegration is an ODT feature as a result, during formulation at least one superdisintegrant is needed. But some scholars have used combinations of different superdisintegrants like crospovidone and starch glycolate [18], combinations of superdisintegrants, and subliming agents like ammonium bicarbonate [19].

Crospovidone is a water-insoluble tablet disintegrant and dissolution agent used at 2–8% concentration in tablets prepared by direct-compression methods [20]. This may vary depending on methods of manufacturing, types of excipients, and nature of active ingredients under investigation [21]. The superior disintegrant capability of crospovidone can be attributed to its rapid capillary action, faster hydration rate, and little tendency of gel formation. Crospovidone's high and rapid water absorption ability has a negative influence on wetting time. Due to its porous particle shape, it causes enormous wicking forces, further expanding and dissolving the tablet into finer particles. Crospovidone increased the crushing strength of tablets in a synergistic manner. This is due to its plastic character and binding capability, in addition to being an efficient disintegration agent; it acts as a highly compressible material in the dry state, hence increasing its concentration from 2–8% considerably enhanced the crushing strength of tablets. Ammonium bicarbonate is chemically inert and when subjected to high temperature and pressure, sublime due to its volatile nature resulting in highly porous structure in the tablets. It is utilized as a porosity-forming agent in tablets at a concentration of 2.5–20%. The solid, crystalline nature of ammonium bicarbonate accounts for its superiority. After sublimation, the leftover fractions of liquid volatile components in tablets solidify and serve as binders, but ammonium bicarbonate in residual concentration does not undergo this transformation and does not alter the mechanical characteristics of tablets [22, 23].

Excipient compatibility is responsible for mechanical strength, while high porosity is the key factor controlling quick disintegration of ODTs. Binder/disintegrant systems with dual benefits have solved both objectives in part. Mannitol has nice flavor and sweetening properties. Microcrystalline cellulose, on the other hand, has better mechanical characteristics for ODTs than mannitol. More than only good binding qualities in an excipient is required for the production of orally disintegrating tablets [24]. Amalgamation of cellulose and polyol-based excipients such as mannitol provides us with a clear criterion for developing directly compressed ODTs [23, 25]. The hardness of ODT is usually preferable between 4 and 8 kg in order to withstand handling during manufacturing, packaging, and transportation [26]. The hardness of tablets depends on the amount and types of binding agent present [27]. Therefore the change in hardness values of different ODTs observed in different amount and type of binding agents [28]. The hardness values for all tested tablets increase as the Microcrystalline cellulose to Mannitol ratio increases [23]. Occasionally sweetening agents like Aspartame (artificial sweetener) noncarcinogenic and can be consumed by diabetes patients, and; flavoring agents like vanillin can be used to mask unpleasant tastes and flavors of the active ingredients even though these are weak in taste masking. Much more intense sweeteners compared with sucrose with acceptable daily intake of 50 mg/kg. Vanilla

flavor is a natural flavor that supplements and complements the sweetening agent [29]. There are many taste-masking techniques that have been reported in addition to adding flavors and sweeteners, coating drug particles with inert agents [30], inclusion complexes [31], microencapsulation [32], solid dispersions [26], molecular complexes of drug with other chemicals and prodrug by using ion exchange resins [33].
