MORPHINE can make it harder to fight off gut infections, microbiologists said
last week. This might explain why intravenous drug users with AIDS seem to
suffer frequent and severe bouts of Salmonella poisoning. Until now,
doctors have tended to blame the infections on immune system suppression by
HIV.
For over a century scientists have known that people who use heroin and
morphine seem more prone to infections, though no one was quite sure why. To
study the drug鈥檚 effect on gut infections, Toby Eisenstein and her colleagues at
Temple University in Philadelphia fed mice with a virulent strain of
Salmonella typhimurium. The mice were also given a surgical implant that
released either morphine or a placebo.
鈥淢orphine dramatically sensitised these mice to infection with
Salmonella,鈥� Eisenstein reports. The animals on morphine all died of
Salmonella poisoning within five days, while only half of the control mice
died. And the mice on the placebo that died took twice as long to do so as those
on morphine.
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The most impressive demonstration of morphine鈥檚 effect came by accident, when
a lab worker fed each mouse around 210 Salmonella organisms, a
hundredth of the planned dose. All the mice receiving morphine that were given
this tiny dose of Salmonella died within five days, while all the
control mice survived.
The observations, which will appear in the April issue of The Journal of
Infectious Diseases, are intriguing because sharing needles for intravenous
drug use is a common cause of HIV transmission. The incidence of
Salmonella infections is 20 times higher in AIDS patients than people with
normal immune systems, and people with HIV can have severe cases of
Salmonella that also affects the brain and lungs.
Doctors have assumed that HIV patients have an increased risk because their
immune systems are suppressed. But Eisenstein thinks morphine may also be
implicated if people with HIV take the drug to control pain or because they are
addicts. Morphine reduces movement of the gut, which may prevent bacteria being
washed out quickly. She also suspects that the drug reduces the ability of
infected cells along the gut wall to produce cytokines, chemicals that summon
help from the immune system.
And it isn鈥檛 only people with HIV who are at risk, Eisenstein adds. She says
it is possible that morphine could also increase the risks for hospital patients
taking it for pain if they become infected with an antibiotic-resistant 鈥渟uperbug鈥�.