Need more drugs to numb the pain? It might be because you received them as a baby. Studies in rats suggest some premature babies might grow up with altered sensitivity to pain and painkillers if they received morphine in intensive care during their first few weeks after birth.
Around 3 per cent of babies in the UK and US are born so prematurely that they need invasive treatments such as surgery or mechanical ventilation to keep them alive. Although acceptance that these babies need pain relief has been slow to grow, most of them will now receive morphine at some point.
Sarah Sweitzer of the University of South Carolina in Columbia treated newborn rats with morphine injections during the first nine days after birth and tested their pain sensitivity later in life. Rats are born so immature that their early development resembles that of a premature baby.
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Even aged 39 days 鈥� the equivalent of adolescence 鈥� rats treated with morphine in infancy seemed to be more sensitive to pain because they withdrew their paws more readily when heated with a lamp or poked with a hair than did the rats that had been given a placebo. When the rats were given morphine, those who had received the drug as babies needed more of it as young adults (Brain Research, ).
鈥淩ats treated with morphine in infancy needed more of it to kill pain when they were young adults鈥�
Premature birth and pain are known to have other long-term repercussions, but the effects of morphine on adults born prematurely have still to be studied. If the rat findings hold true for people, we may need to change the approach to effective pain relief as premature babies grow up, says Sweitzer.
Kanwaljeet Anand, a neonatal pain expert at the University of Arkansas agrees: 鈥淚t鈥檚 high time we did some follow-up research on children who received morphine as premature babies.鈥�
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