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The risk of birth defects for babies if their mothers use alternatives to penicillin during pregnancy ‘

Frequently used antibiotics during pregnancy increase the risk of birth defects in babies, a study suggests.

It found macrolides – a group of antibiotics commonly used to treat chest and urinary tract infections – to significantly increase the risk of heart, genitals and brain.

Although most antibiotics, such as penicillin, are safe during pregnancy, the study raises new concerns about the macrolides group, including common antibiotics such as erythromycin, clarithromycin and azithromycin.

These treatments have been given to about 3 percent of pregnant women in the UK in the last 26 years, according to a study by researchers at University College London.

In total, 31 percent of mothers take antibiotics during pregnancy, and 21 percent use penicillin. But macrolides are among the most prescribed for the many women who are allergic to penicillin.

University College London scientists said their findings raised concerns about a type of antibiotic called macrolides, which are used to treat bacterial infections in people who are allergic to penicillin (stock image)

University College London scientists said their findings raised concerns about a type of antibiotic called macrolides, which are used to treat bacterial infections in people who are allergic to penicillin (stock image)

The research team, whose work is published in the British Medical Journal, discovered that babies whose mothers took macrolides in the first trimester of pregnancy were about 55 percent more likely to be born with a defect than those whose mothers took penicillin took.

Some macrolides contain warnings that they should not be taken during pregnancy. But others – including erythromycin, the most commonly used macrolide – are officially listed as “not known to be harmful” during pregnancy.

Researchers used a database of just over 1 million children born in the UK from 1990 to 2016, kept up to the age of six. 105,000 of them had macrolides or penicillin during pregnancy.

Major malformations were present in 186 of the 8,632 children whose mothers were prescribed macrolides at some point during pregnancy and 1,666 of the 95,973 whose mothers were prescribed penicillin during pregnancy.

After adjusting the figures for other factors that could influence the findings, the researchers calculated that 28 out of every 1,000 babies whose mothers took macrolides during the first three months of pregnancy developed birth defects.

Macrolides led to a risk of 55 percent greater than for penicillin, resulting in 18 defects per 1,000 births, about the same overall risk that every baby with a health problem is born.


Macrolide antibiotics are a type of medicine that is very similar to penicillin.

They can perform the same function for many infections and are generally safe for people to take if they are allergic to penicillin.

About 0.5 percent of people – one in 200 – have a penicillin allergy.

Macrolides can be used to treat sexually transmitted diseases, skin infections and lung infections such as pneumonia.

The most important types of macrolides can be identified by their names, which end with ‘mycin’.

Main types include:

Erythromycin, used to treat syphilis, chlamydia, urethritis and pneumonia

Azithromycin, which can be used for flu, chlamydia, urethritis, gonorrhea, typhoid, trachoma and Lyme disease

Clarithromycin, which is used to kill bacteria called Helicobacter pylori, which can cause stomach ulcers

Spiramycin, used to treat toxoplasmosis

Source: National Institute for Health and Care Excellence (NICE)

Although the greatest risk was seen in the first trimester, the use of macrolides at any time during pregnancy increased the risk of birth defects by 23 percent compared to penicillin.

Professor Ruth Gilbert, researcher at the UCL Great Ormond Street Institute of Child Health, said, “Our findings suggest that it is better to avoid macrolides during pregnancy if alternative antibiotics can be used.”

But she added, “Women should not stop taking antibiotics when necessary, because untreated infections pose a greater risk to the unborn baby.”

The team emphasized that the size of the risk remains very low.

Researcher Heng Fan said, “These findings suggest that another four children would be born with cardiovascular malformations for every 1,000 children who were exposed to macrolides instead of penicillin in the first trimester of pregnancy.”

Dr. Pat O’Brien, vice president of the Royal College of Obstetricians and Gynecologists, said last night: “It is important to realize that untreated infections during pregnancy, such as urinary and breast infections, can harm both mother and baby, so it is important that they are treated correctly.

“Based on the findings of this study, it seems reasonable to be cautious about using this type of antibiotic during pregnancy until further research is done to clarify whether there is really an increased risk.

“Other antibiotics, such as penicillin, that are safe during pregnancy, are alternatives.”

But he added: “In some cases, for example in women who are allergic to penicillin and where the infecting bacteria are resistant to other antibiotics, erythromycin may be the only suitable antibiotic.

“In this situation, it seems highly likely that the risks of untreated infection are greater than the potential risks of using erythromycin.”

But Gino Pecoraro, associate professor at the University of Queensland in Australia, said “dredging data” to look for adverse effects has become a “worrying trend in medical research.”

“These observational studies have insufficient strength to prove the causal relationship and can cause unnecessary anxiety in pregnant women and sometimes even lead to denial of what may be important treatment options,” he warned.

“The benefits of using a drug should be weighed against the risks to the mother and the developing baby of not giving treatment, and where a safer and available alternative exists, that drug should be preferred.”