**4. Drug delivery approaches**

### **4.1 Drug delivery by oral route**

Drug delivery by oral route has traditionally been the most prevalent option for designing delivery systems. Drug release in oral delivery system may be controlled by dissolution, diffusion, pH, or osmosis [38]. The usage of CDs in an oral delivery system is to increase the rate at which dissolution occurs—forming inclusion complexes with CD aids in increasing the solubility of drugs and hence transport of drugs across aqueous phase to lipid membrane in GIT [39]. The hydrophobic derivatives of CDs are mostly employed to accomplish this goal. In case of buccal and sublingual routes, rapid increase in drug concentration can also be achieved by complexation; however, in order to exhibit the therapeutic effect, drug must need to get released from the complex. For sublingual route, it is a little bit difficult since the amount of saliva as well as contact time is limited [40].

Cyclodextrins especially hydrophobic ones, that is, ethylated CDs, are also very important in achieving site-specific or sustained drug release. Additionally, cyclodextrins have productively been utilized in matrix tablets as well as osmotic pumps to control the drug release [41].
