**4.2 Ocular drug delivery**

The primary treatment of an ocular aliment is mainly topical application of drug as aqueous solution. The current findings ascertain that cyclodextrin molecules are helpful components in ocular preparations, since they can enhance the solubility, stability, and consequently bioavailability of the ophthalmic formulations [42]. Among the CDs, hydrophilic cyclodextrins, mainly SB *β*-CD and HP *β*-CD, are reported to be most compatible and nontoxic [43]. It is well known that only a small amount an ophthalmic drug can actually reach systemic circulation, but increasing the availability of a drug at corneal surface through the CD complexation can easily enhance ocular bioavailability of hydrophobic drugs [44].

## **4.3 Nasal drug delivery**

In order to have systemic absorption, drug must have optimum solubility in nasal fluids. Moreover, an optimum nasal formulation also must not have any effect on the defensive functions of cilia in respiratory tract. Both hydrophilic and hydrophobic CDs are the highly employed in this regard, as they can enhance the solubilization as well as the permeation, correspondingly. Besides, they are highly effective in small concentration and stereotypically inert from toxicological perspective [45, 46].

## **4.4 Transdermal drug delivery**

Stratum cornea serves as the main barrier in the delivery of drugs through the skin. Various penetration enhancers are often employed to enhance the delivery across the barrier. Owing to the hydrophobic properties, cyclodextrins have the ability to deliver across water diffusion layer; however, if absorption is dependent on the lipophilic barrier solely, CDs are unable to deliver the drug dermally. Therefore, suitable selection of an aqueous vehicle is highly important [32, 47].
