*3.7. Trans-Corneal Permeation*

Goat cornea was used for the ex vivo drug permeation investigations for the optimized SLNs (CL10) and control (solution). Various studies have used the goat membrane as a barrier, as this membrane is multi-layered and mimics the human corneal membrane [54]. It is well known that the physico-chemical characteristics of the drug, physiology of the membrane, and the availability of transport routes can affect the permeation of drug molecules into and through the biological membrane [55,56]. The amount of clarithromycin permeated through the cornea membrane from the formulation and control are depicted in Figure 11. Two distinct permeation profiles were noticed, with

lipid nanoparticle (CL10).

greater flux (30.45 µg/cm2/h; *p* < 0.0001) exhibited by CL10 when compared with control (10.94 µg/cm2/h). In the case of CL10, permeation was rapid in the initial 3 h (142.2 <sup>±</sup> 14.1 <sup>µ</sup>g/cm<sup>2</sup> ), while it was relatively slow and low with the control (33.7 <sup>±</sup> 11.1 <sup>µ</sup>g/cm<sup>2</sup> in 3 h). The greater permeation noticed in the optimized CL10 indicates that the pharmaceutical characteristics of the prepared SLNs (Table 8) are ideal for cornea permeation. Indeed, the higher clarithromycin permeation observed with CL10 suggests that the drug transport could be prominently due to the nanoparticles, as the drug permeation was very low in the control. Moreover, the greater drug concentration above therapeutic levels observed here is also important, as it will avoid microbial resistance. Overall, the observed data here signifies that the SLN could be an ideal carrier for the ocular delivery of clarithromycin. *Pharmaceutics* **2021**, *13*, x FOR PEER REVIEW 18 of 24

**Figure 10.** Representative size distribution curve (**a**) and zeta potential distribution (**b**) of optimized clarithromycin solid lipid nanoparticle (CL10). *Pharmaceutics* **2021**, *13*, x FOR PEER REVIEW 19 of 24

higher clarithromycin permeation observed with CL10 suggests that the drug transport could be prominently due to the nanoparticles, as the drug permeation was very low in the control. Moreover, the greater drug concentration above therapeutic levels observed **Figure 11.** Cumulative amount of clarithromycin permeated through the goat cornea from solid lipid nanoparticles (CL10) and control (solution). Data represented are mean ± SD (*n* = 6). **Figure 11.** Cumulative amount of clarithromycin permeated through the goat cornea from solid lipid nanoparticles (CL10) and control (solution). Data represented are mean ± S.D. (*n* = 6).

here is also important, as it will avoid microbial resistance. Overall, the observed data here signifies that the SLN could be an ideal carrier for the ocular delivery of clarithromycin.

the lipid nanoparticles were coarsely spherical in shape and uniformly distributed. The particle size was found to be in the range of 100–200 nm. The particle size range observed in TEM image was in good agreement with the values observed in particle size analysis.

**Figure 12.** Surface morphology of optimized clarithromycin solid lipid nanoparticles (CL10). Red

Eye irritation score from individual rabbits was added to obtain the total irritation score, which was subsequently divided by the total number of eyes used for the ocular irritancy test to obtain the final eye irritation score. The calculated eye irritation score in

arrow indicates the diameter of nanoparticle.

*3.9. Ocular Compatibility*

A representative TEM micrograph of the optimized SLN (CL10) is shown in Figure

*3.8. TEM*
