Prodrugs incorporated into nanotechnology-based drug delivery systems for possible improvement in bioavailability of ocular drugs delivery

Numerous systems have been designed during the past three decades to improve bioavailability of ophthalmic drug delivery,including:ocular prodrugs and nanotechnology-based drug delivery system.The former can improve the efficacy of ocular drug via enhancing corneal penetration of ocular drugs,prolonging their duration of action and/or reducing the systemic side-effects,unfortunately,some characteristics of the pro-drugs,such as poorly aqueous stability,poorly aqueous solubility and severe eye irritation probably,limit their clinical practice and cannot be ignored.As we all know,nanotech-nology for ocular drug delivery can carry poorly soluble drugs,protect the encapsulated molecules from hydrolysis,control the rate of drug delivery and prolong the precorneal retention of drugs.All of these merits may solve the problems in the utilization of ocular prodrugs and increase the bioavailability of ocular drug delivery.By reviewing recent ad-vances of prodrugs and nanostructures in ocular drug delivery,this paper focus specifically on the promising prospects of nanocarriers overcoming the drawbacks of prodrugs for ophthalmic drug delivery by precorneal routes.

Comparative study on pharmacokinetics and toxicity of intravitreal and sub-Tenon injection of triamcinolone acetonide in ocular tissues

AIM:To compare the differences in kinetics,distribution,and toxicity of triamcinolone acetonide(TA)between the injection methods,sub-Tenon and intravitreal injections in rabbit ocular tissues.METHODS:TA was injected into the vitreous or the sub-Tenon in rabbits.For pharmacokinetic study,rabbits were sacrificed periodically and then TA in blood and ocular tissues(retina/choroids,vitreous,and aqueous humor)were measured over 91 d.For toxicological study,clinical signs,slit-lamp microscopic examination,ophthalmological test were performed.The eyeballs and surrounding tissues were collected and fixed with glutaraldehyde-formalin solution,and then paraffin embedded for histological investigation.RESULTS:Higher levels of TA were distributed in the intraocular tissues when injected into the vitreous compared to the sub-Tenon.Conversely,TA level was remarkably lower in the rabbits which received intravitreal TA injections than those treated with sub-Tenon injection throughout the study period in plasma.Optical discharge probably caused by systemic circulation of TA was observed by receiving sub-Tenon TA injection.Meanwhile,technicassociated toxicological ocular symptoms and findings were more frequently observed in intravitreal injection than in sub-Tenon injection.CONCLUSION:There are significant differences in kinetics and distribution of TA in vitreous body,aqueous humor and plasma,between the two injection methods.Although further study is needed to explain the species difference between human and rabbit,it is assumed that the difference in the frequency of intraocular pressure elevation and cataract formation by TA between the two injection methods are directly related to the TA concentrations in aqueous humor and vitreous body in each injection methods.Systemic toxicity and technic-associated toxicity are also closely related to kinetics of TA in plasma and each injection method itself,respectively.