Ocular pharmacokinetics studies the mechanisms of drug absorption, distribution, metabolism, and excretion in the eye. In vivo pharmacokinetic studies of drug delivery to the posterior eye segment can be performed in three ways: 1) administering drugs to rabbits and analyzing tissue, 2) using microdialysis probes in rabbits, or 3) administering fluorescent drugs to rats and analyzing under a microscope. Examples are provided of studies using fluorescent dyes and drugs administered via eye drops in various animal models, with outcomes like drug localization in ocular tissues.

1. Ocular Pharmacokinetics
By definition; ocular pharmacokinetics is the study of the mechanisms of drug absorption, distribution, metabolism, and excretion;
onset of action; duration of effect; biotransformation; and effects and routes of excretion of the metabolites of a drug in the eye.
For assessing drug delivery to posterior segment of eye, in vivo pharmacokinetic studies could be performed by three ways
Table 1. Comparison of three ways of performing in vivo ocular pharmacokinetic studies
S.
No.
First way Second way Third way
1 Instillation of topical ocular dosage form into
rabbit eye at different time points and sacrifice
of animals followed by collection of different
tissue and analysis by LC/MS
Anesthetize rabbits, implantation of
microdialysis probe into vitreous chamber of
rabbit eye, instillation of topical ocular dosage
form into rabbit eye, collection of sample at
every 20 minute using probes and analysis by
LC/MS
Instillation of dye/fluorescent loaded
topical ocular dosage form in rat eye,
sacrifice animal at different time
points, eye enucleation, analysis under
fluorescence/confocal microscope
2 Rabbit at each time point Experiment lasts for 10hour in single rabbit Rat at each time point
3 Sacrifice rabbit at each time point No need to sacrifice rabbit, Rabbit can be
reused
Sacrifice rat at each time point
4 Need expertise to perform this Need expertise as well as sophisticated
equipment
Feasible
5 Need large number of rabbit at different time
point
Need fewer rabbits Rats needed, affordable
6 Expensive Very expensive Feasible

2. Table 2. Examples of in vivo ocular pharmacokinetic studies for drug delivery to posterior segment of eye using dye/fluorescent in animals via topical route
S.
No.
Year Dye/Drug/Formulation Animal Outcome Reference
1. 2020 Coumarin
6/Dexamethasone/Chitosan
oligosaccharide valylvaline-
stearic acid nanomicelle
Rats (Xu et al.
2020)

3. 2. 2019 Cumarin 6/Triamcinolone
acetonide/Chitosan coated
liposome
Mice
Figure. OCT images of posterior segment of the mouse eye after eyedrop application of
C6-liposomes/C6-CHL at different times.
(Li et al.
2019)

4. 3. 2019 FITC/Tacrolimus/Marinsolv
solution
Pig (Siegl et
al. 2019)
4. 2019 Coumarin 6/Triamcinolone
acetonide/Chitosan coated
liposome
Rat (Khalil et
al. 2020)

5. 5. 2019 Doxorubicin/Dexamethasone
disodium
phosphate/Glycosarcosine
anchored layered double
oxide liposome
Rabbit (Gu et al.
2019)
6. 2019 Coumarin 6/Flucinolone
acetonide/Microemulsion
Rat (Gupta et
al. 2019)

6. 7. 2018 Coumarin 6/Triamcinolone
acetonide/Microemulsion
Rat (Raval et
al. 2018)

7. 8. 2017 Coumarin 6/Coumarin
6/PLGA nanoparticle
Mice (Tahara
et al.
2017)

8. 9. 2017 Coumarin 6/High density
lipoprotein/Liposome
Mice (Suda et
al. 2017)

9. 10. 2016 Coumarin 6/Liposome Mice (Hayashi
et al.
2016)

10. 11. 2014 Transferrin/Plasmid
DNA/Liposome
Rat (Lajunen
et al.
2014)
12. 2013 Coumarin 6/Lipid emulsion Mice (Ying et
al. 2013)

11. 13. 2013 Coumarin 6/ Liposome Mice (Sasaki et
al. 2013)

12. 14. 2011 Nile red/Triamcinolone
acetonide/Nanostructured
lipid carrier
Mice (Araujo
et al.
2011)

13. 15. 2010 Coumarin 6/Liposome Mice (Inokuchi
et al.
2010)

14. 16. 2009 Coumarin 6/Liposome Mice (Hironaka
et al.
2009)

15. 17. 2009 FITC/Vasostatin Rat (Sheu et
al. 2009)
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