- MONDAY, Aug. 25 (HealthDay News) — Breast-feeding moms who take
medicines containing codeine may be unwittingly risking the health of
their infant, new Canadian research suggests.

The study indicates that a relatively rare genetic predisposition
causes some women to metabolize codeine-laced drugs into morphine far
faster than normal — possibly harming the infant's central nervous system
in the process.

In such cases, the threat of a morphine overdose appears to be
reversible if the woman stops taking the medication. However, for mothers
with the genetic vulnerability, the unabated ingestion of codeine and
gradual build-up of morphine in a baby's system can prompt extreme
sleepiness, abnormal breathing, and even death, the researchers
warned.

The finding echoes a public health advisory issued by the U.S. Food and
Drug Administration in 2007.

“Codeine itself doesn't have any pain-relieving effects, but our body
changes it into morphine, and that's what combats the pain,” explained
study author Parvaz Madadi, a doctoral candidate in the department of
physiology and pharmacology at the University of Western Ontario, in
Canada.

“The problem is that your genetic makeup makes more or less of it,” she
noted. “So this is where the risk lies, because you can't know in advance
what that predisposition would be, unless you would do a genetic test,
which is not standard routine at this point. So while it would not be a
problem in all cases, I would say that codeine cannot be considered a safe
drug for some mothers who are breast-feeding their infants.”

Madadi and a team of Canadian researchers published the findings in the
Aug. 20 online issue of Clinical Pharmacology &
Therapeutics.

The study authors pointed out that pain-relief medications are commonly
prescribed for new mothers, given that almost half of all babies are
delivered by either Caesarean section or episiotomy.

Given that the American Academy of Pediatrics recommends codeine as
“compatible” with breast-feeding, and given that an estimated 80 percent
of North American mothers breast-feed, Madadi and her colleagues calculate
that upwards of 40 percent of all new mothers may be breast-feeding while
consuming codeine for post-delivery pain.

Among that group, the researchers noted that between 1 percent and 10
percent of mothers with white European ancestry appear to have the risky
genetic variant that causes morphine overproduction. Prior research
indicates that the figure might be higher for other ethnicities.

Madadi noted that the current research effort was launched following
the death of a Canadian infant due to the excessive ingestion — following
12 days of breast-feeding — of codeine-produced morphine.

In that instance, the mother, who was prescribed codeine-containing
painkillers following an episiotomy, was later found to have the
problematic genotype.

To explore the issue, the research team analyzed DNA samples collected
from 72 mothers across Canada who consumed post-delivery codeine between
2004 and 2007. All the women also participated in a telephone survey to
gauge the health of the mother and the central nervous system of the
child — both before, during and after codeine consumption.

Nearly one-quarter of the infants exhibited some central nervous system
depression — manifested by reduced alertness — while breast-feeding
during maternal codeine ingestion.

Among this group, mothers were found to have consumed, on average,
almost 60 percent more codeine than mothers with healthy babies. This led
the team to conclude, in fact, that excessive codeine consumption while
breast-feeding can compromise a baby's health, whether or not the mother
is one of the relatively few affected by a genetic predisposition to
overproduce morphine.

But when honing in on the genetic front, the researchers indeed found
that two mothers of symptomatic children carried the problematic genetic
predisposition. In these two instances, the child's reaction to codeine
consumption was particularly severe, with one baby ultimately dying as a
result.

Julie Kable, an assistant professor of pediatrics at Emory University
School of Medicine in Atlanta, said that the work represents “the wave of
the future in science.

“The basic nature of this finding does not surprise me, given that this
is where science is going, with a huge effort being made to better
understand the interaction of one's genes with exposure to various
substances. And it's not unheard of for this kind of science to lead to an
altering of ob/gyn practice. It should be said, for example, that it
wasn't so long ago — in the 60s and 70s — that women were actually given
alcohol to stop premature labor. So, the possibility that this is true
does create a burden to do the appropriate testing before we make such
prescriptions.”

More information

For more on codeine consumption and breast-feeding, visit the U.S. Food and Drug Administration.