A new technique to deliver drugs to eyes without making them water
TEARS tend to wash away most of the
drugs that are administered as drops
into the eyes. Now, scientists have developed an ilinproved way of delivering a
drug to the eyes by making it tear-resistant, rendering it 4 times more likely to reach its target (New Scientist, Vol 14& No 1974).
Develpped by Thorsteirm Loftsson
and Einar',Stefansson of the Universitv
of Iceland, the improved systernallows
many drugs that are greasy and difficult
to dissolve in water, to penetrate the eve
surface directly without being lost to
tears. Evidently, these hydrophobic
drugs cause irritation and blurred vision
if used as oil-based drops or ointments.
Taken as tablets means its absorption
through the stomach lining and subsequent spread throughout the body
before reaching the eye. This heightens
risk of side-effects of the drug besides
being more expensive due to the requirement of a higher dosage of drug.
Researchers in the past. worked on
improving the system by using cylindrical molecules called cyclodextrins,
whose inner cavity is hydrophobic and
is used to trap the drug molecule. The
molecule's outer surface being hydrophilic, sticks to the cornea on contact.
The drug molecule then slips out of the
cavity right through the hydrophobic
cornea into the eye. However, by using
this method, 95 per' cent of the drug is
washed away with tears before it penetrates the eye.
Scientists now have enfolded
cyclodextrin molecules in a large polymer that can dissolve in water. A "Co-
complex" is formed by heating cyclodextrin along with the polymer and anantiglaucoma drug Dextamethosone.
The largeness of the polymer makes it
resistant to tears by binding it more
strongly to the cornea, thus giving the
drug longer time to enter the eye.
Another antiglaucoma drug called
Azetazolamide, which was until how
administered as tablets, was also tested
in the form of a "co-complex". It was
found to reduce internal eye pressure up
to 14 per cent that is more favourable
than with the drug Timolol maleate,
the most effective antiglaucoma drug in
the market, but which is unsuitable for asthma patients.
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