No tear jerker, this
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.