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Editors Selection IGR 22-2
Medical Treatment: Long-lasting drug delivery
Comment by Tina Wong on:
57479 28-day intraocular pressure reduction with a single dose of brimonidine tartrate-loaded microspheres, Fedorchak MV; Conner IP; Medina CA et al., Experimental Eye Research, 2014; 125: 210-216
This study describes the use of microspheres as a drug delivery carrier for controlled drug delivery of anti-glaucoma drug, brimonidine tartrate, by a single subconjunctival injection. Both in-vitro and in-vivo studies were conducted as a proof of principle and showed extended IOP reduction in normotensive rabbits over a 28-day period.
In order for a drug delivery system to really indicate clinical promise, a few critical questions on the delivery system must be addressed.
Calculation of the entrapment efficiency as well as efforts to remove un-entrapped drug from the microspheres would provide additional information on the characteristics of the microsphere delivery platform as well as to distinguish the localization of the drug, i.e., whether the drug is loaded in the core or on the periphery of the microspheres for more accurate characterization.
Supporting studies on the mechanism of release are essential to determine the fate of the particles under in vivo conditions
Initial two-day-released amounts are not reported here, and therefore it is plausible to consider that the drug may not be distributed homogenously in the microspheres, therefore lending to an initial burst effect in the first few days. As a consequence, this could have an effect on the total extended release period of the microsphere system and its ability to provide steady consistent IOP lowering in vivo. Interestingly, the release rate per day hovers around the maximum allowable brimonidine concentration which would appear that the system is quite efficient at loading brimonidine. However, modifications into PLGA microspheres to reach a release rate in between the minimum and maximum allowable concentrations would be more ideal.
It is hard to confirm by visual inspection alone that particle degradation occurs by day 35. Supporting studies on the mechanism of release are essential to determine the fate of the particles under in vivo conditions. Although the formulation appears to demonstrate some positive effects in animals, it is clear that more mechanistic work is required in the understanding of the system and to establish the actual release in vivo and longer term effect of a single-dose application.
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