CATHETERS made from a polymer that slowly releases an antibiotic could
prevent thousands of hospital patients dying from infections every year. The
antibacterial polymer could also thwart infections around more permanent
implants, such as pacemakers, say researchers at the University of Washington in
Seattle.
Because repeated injections can damage veins, patients on lengthy courses of
drugs have a catheter inserted in a vein. But catheters can often pick up stray
microorganisms from the doctors, nurses or even the patients themselves. 鈥淭hese
devices are sold sterile, but operating rooms are not perfect and patients are
teeming with bacteria,鈥� says Buddy Ratner who leads the research team.
If the bacteria multiply enough, they can be very hard to remove. 鈥淥nce
bacteria get on a device they form a film that makes them far more difficult to
kill off,鈥� explains Ratner. Such biofilms, based on polysaccharides, can protect
diverse populations of bacteria
(New 杏吧原创, 31 August 1996, p 32).
It takes around twenty times the normal dose of antibiotics to get rid of them.
And often not for long.
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鈥淵ou鈥檒l find that you use antibiotics for a couple of weeks, but it鈥檚 not
long before the patient鈥檚 back in with a further infection,鈥� says Phil Stewart
of Montana State University鈥檚 Center for Biofilm Engineering. American estimates
suggest that up to half of the 350 000 blood infections picked up in hospital
are caused by infected catheters. And up to 40 per cent of these are fatal.
Ratner and his colleague Connie Kwok tackled the problem by mixing
polyurethane鈥攖he material used to make catheters鈥攚ith polyethylene
glycol and an antibiotic called ciprofloxacin. Then he coated the polyurethane
with an ultrathin barrier of another polymer called butyl methacrylate.
Blood plasma passes through the permeable butyl methacrylate coating and
dissolves the polyethylene glycol. This makes the polyurethane porous,
increasing the surface area that comes into contact with the plasma which
leaches the antibiotic out of the polyurethane. The butyl methacrylate coating
acts as a barrier to the antibiotic, regulating its release.
Ratner tested the polymer films by first measuring how much of a test drug
they released into water. He found that, with the barrier coating, the drug was
released slowly over five days at a concentration high enough to kill the
bacterium Pseudomonas aeruginosa. Further tests also showed that the
same bacteria were four times less likely to stick to the films than to normal
polyurethane.
鈥淚 absolutely think that binding chemicals to catheters is a very good way to
go,鈥� says Richard Wenzel, Head of Internal Medicine at Virginia Commonwealth
University. 鈥淎lthough if ciprofloxacin is released, you have to think about
antibiotic resistance鈥攊t might be better to use a drug we don鈥檛 use for
迟丑别谤补辫测.鈥�