Pharmaceutical Manufacturing Handbook: Production and

REFERENCES 785
stability of incorporated drugs with potential increase in bioavailability; hence these
systems could be a suitable alternative to conventional ocular formulations. So far,
only few investigators [124 – 127] have considered the use of MEs for ocular drug
delivery. Their work was solely focused on o/w MEs as ocular delivery carriers.
Recently Alany et al. [128] reported on w/o MEs formulated using a blend of two
nonionic surfactants (Crillet 4 and Crill 1), an oily component (Crodamol EO), and
water. These systems were shown to be capable of undergoing a phase change to
lamellar liquid crystals upon aqueous dilution. The ocular irritation potential of the
individual components and fi nal formulations was assessed using a modifi ed hen ’ s
egg chorioallantoic membrane test (HET - CAM), and the preocular retention was
investigated in the rabbit eye using gamma scintigraphy. The authors demonstrated
that the retention of ME systems was signifi cantly greater than an aqueous solution.
The rapid clearance of the w/o ME formulated with 10% water compared to the
LC system indicated that phase change is less likely to take place in the rabbit eye
[128] . It was also concluded that w/o MEs may be of value as vehicles for the ocular
drug delivery of irritant hydrophilic drugs as they appear to have a protective effect
when evaluated using a modifi ed HET - CAM test [128] . The potential of bicontinuous
ME systems as vehicles for ocular drug delivery is yet to be investigated. A
recent review reported on the potential of MEs as ocular drug delivery systems;
however, submicrometer emulsions and systems requiring energy input to prepare
were also covered and classifi ed as MEs [129] .
5.10.7
CONCLUDING REMARKS
Microemulsions represent an exciting opportunity for pharmaceutical formulators
and drug delivery scientists. They are easy to prepare and thermodynamically stable.
Moreover, they can accommodate drugs of different physicochemical properties and
protect those that are labile. They have the potential to increase the solubility of
poorly water soluble drugs, enhance the bioavailability of problematic drugs, reduce
patient variability, and offer an option for controlled drug release. A critical look at
the current literature shows that exciting and promising research is taking place. It
is only a matter of time before new ME - based products will fi nd their way to the
market following the successful introduction of Sandimmune Neoral.
REFERENCES
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delivery systems , Adv. Drug Del. Rev. , 45 ( 1 ), 89 – 121 .
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