CHEMICAL components of a pregnancy test drug linked to serious birth defects in the 1960s and 70s can cause deformities in fish embryos, Scottish tests show.
Campaigners blame Primodos for causing miscarriages and a range of health problems in newborns, including missing limbs, brain damage and abnormalities in internal organs.
The hormone pregnancy test (HPT) was prescribed to an estimated 1.5 million women in the UK before being withdrawn from the market in 1978.
The move followed studies connecting HPT use with a wide range of health problems in infants.
Now newly-published research has reveals that components of the controversial drug caused deformations to embryos just hours after exposure.
The findings are linked to tests using zebrafish embryos and concern substances still used in other forms.
Study leader Dr Neil Vargesson, of Aberdeen University, said the work does not provide conclusive proof that the tablets caused harm to humans.
However, the report states that the damage was "extremely rapid", with the embryos showing significantly reduced movement within one hour and "obvious morphological defects" within four hours.
The research, published in the Scientific Reports journal, states that components Norethisterone acetate and Ethinyl estradiol accumulate in the developing embryo for at least 24 hours and "cause embryonic damage in a dose and time responsive manner", adding: "The damage occurs rapidly after drug exposure, affecting multiple organ systems."
The substances are still used in other medications including treatments for endometriosis and contraceptives.
Vargesson said: "At the moment the scientific research into whether or not Primodos caused these birth defects is inconclusive.
"What this study highlights is that there is a lot still to be learned about Primodos and more widely its components effects on mammals.
"Our experiments with the zebrafish embryos shows quite clearly the effects the Primodos components have.
"This does not mean it would do the same in humans of course, we are a long way from saying that but we need to carry out more research into these components because they are still in drugs today and in some cases in much higher doses than those found in Primodos.
"The assumption by some previously has been that the doses given to mothers was too low to cause any damage but our study shows that the levels of Primodos' components accumulate in the embryos over time because they don't have a fully functional liver that can break down the drug.
"This, too, is new information and if the same thing happens in mammals, these drugs could build up in the embryo to much higher levels than shown in the mother's blood."
A review into HPTs by the Commission on Human Medicines last year concluded scientific evidence "does not support a causal association" between their use and birth defects or miscarriage.
However, campaigners called the review a "whitewash", saying the expert working group did not examine all of the available evidence on the use of the drugs.
Marie Lyon, who chairs the Association for Children Damaged by Hormone Pregnancy Tests, welcomed the new study, adding that the campaign group had "no confidence" in the Commission on Human Medicines report.
Dr June Raine, director of vigilance and risk management of medicines at the Medicines and Healthcare products Regulatory Agency (MHRA), said: "Patient safety is our highest priority and the safety and effectiveness of all available medicines is kept under constant review. As new data comes to light, action is taken as appropriate to make sure the benefits of medications outweigh the risks."
She added: "The expert working group of the Commission on Human Medicines conducted a comprehensive independent scientific review of all available evidence including this then-unpublished scientific study and their overall conclusion was that the available scientific evidence, taking all aspects into consideration, did not support a causal association between the use of hormone pregnancy tests such as Primodos during early pregnancy and birth defects or miscarriage.
"The expert working group made a number of future-facing recommendations and our focus is now on implementing these.
"While the review cannot take away from the very real suffering experienced by the families involved, it helps shape the path to further strengthen the scientific evidence which supports safety monitoring of medicines in pregnancy."
Livingston MP Hannah Bardell, who has been campaigning on behalf of constituent Wilma Ord and her daughter Kirsteen, is on Westminster's All-Party Parliamentary Group on Hormone Pregnancy Tests.
She said the MHRA should have included the work in its review, stating: “While this is welcome news, we’ve known about this research for a long time and the crux of this is that the information was already out there and was deliberately not considered by the MHRA.
“Dr Neil Vargesson presented his findings at a conference in Cambridge in January 2017, showing evidence of damage to fish embryos when injected with Primodos.
“The families need the truth and this has been such an ordeal for them. Hopefully Dr Vargesson’s study will force the Prime Minister to take note and order a judge led inquiry without delay.”
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