Botulinum toxin type A in pregnancy

Abstract

Question My patient received 62 units of botulinum toxin type A (BTX-A) for facial lines. Two weeks later, she found out that she was pregnant. Will this cause any harm to her fetus?

Answer Botulinum toxin is not expected to be present in systemic circulation following proper intramuscular or intradermal injection. Moreover, BTX-A, which has a high molecular weight, does not appear to cross the placenta. From the 38 pregnancies reported in the literature, including women who had botulism poisoning during pregnancy, exposure to BTX-A does not appear to increase the risk of adverse outcome in the fetus.

Botulinum toxin type A (BTX-A) is a purified neurotoxin from the bacterium Clostridium botulinum. It has numerous medical applications such as treatment of cervical dystonia, focal spasticity, strabismus, achalasia, blepharospasm, hyperhidrosis, migraine, and tension headache.¹ It has also become popular among dermatologists and plastic surgeons for its cosmetic indications to temporarily paralyze facial muscles and diminish wrinkles in the skin.² With more women delaying pregnancy until later in life, inadvertent exposure of pregnant women to BTX-A is likely to occur at a greater frequency.

Botulinum toxin is a large protein with a high molecular weight (150 kD).² When injected intramuscularly in recommended doses, BTX-A is not expected to enter systemic circulation.² Therefore, BTX-A is unlikely to be present at the maternal-fetal interface.

In rabbits, botulinum toxin was not detectable in the placenta or in the fetuses when given intravenously in highly lethal doses.³ However, fetal malformations and abortions were reported in rabbits with daily injections of BTX-A (doses of 0.125 U/kg and 0.5 U/kg daily, and 2 U/kg, 4 U/kg, and 6 U/kg).² Similar adverse fetal outcomes were not found in pregnant mice.²

Information about exposure to botulinum toxin in human pregnancy is limited to case reports and a survey.^4–18 Seven cases of women with botulism poisoning in either their second or third trimester have been reported.^4–10 No evidence of birth defects or infantile botulism in the neonates was noted in any case. In one case, when maternal paralysis was severe, fetal movements were the only visible movements in her body.⁶ In 2 of the above cases, infant serum was taken and no botulinum toxin was detected.^4,10 An additional 28 pregnancies with exposure to BTX-A therapy (at least 18 of 28 had first-trimester exposure) reported 25 normal live pregnancies, 1 therapeutic abortion, and 2 spontaneous abortions.^11–16 Both women who had spontaneous abortions had histories of spontaneous abortions. There are also 3 reports of first-trimester use of BTX-A for cosmetic indications.^17,18 Two healthy babies were delivered, and no details were provided for the third case.

With proper administration of BTX-A, it is not expected to enter systemic circulation. Therefore, based on its local action and on the existing data, administering BTX-A to a pregnant woman is not expected to cause any fetal harm. However, until more data are available, benefits and potential risks to both the mother and the infant should be considered when recommending BTX-A injection to a pregnant patient.

Motherisk

Motherisk questions are prepared by the Motherisk Team at the Hospital for Sick Children in Toronto, Ont. Dr Tan and Ms Kim are members, Dr Koren is Director, and Ms Bozzo is Assistant Director of the Motherisk Program. Dr Koren is supported by the Research Leadership for Better Pharmacotherapy during Pregnancy and Lactation. He holds the Ivey Chair in Molecular Toxicology in the Department of Medicine at the University of Western Ontario in London.

Do you have questions about the effects of drugs, chemicals, radiation, or infections in women who are pregnant or breastfeeding? We invite you to submit them to the Motherisk Program by fax at 416 813-7562; they will be addressed in future Motherisk Updates. Published Motherisk Updates are available on the Canadian Family Physician website (www.cfp.ca) and also on the Motherisk website (www.motherisk.org).