UMEM Educational Pearls

Category: Toxicology

Title: Antidote Safety in Pregnancy

Keywords: antidote, pregnancy, ethanol, amyl nitrate, methylene blue, penicillamine, lorazepam, diazepam (PubMed Search)

Posted: 2/13/2013 by Bryan Hayes, PharmD (Emailed: 2/14/2013) (Updated: 2/14/2013)
Click here to contact Bryan Hayes, PharmD

Most antidotes have not been adequately studied in pregancy and hold a Pregnancy Risk Category 'C' by the FDA. However, there are a few antidotes that hold a category 'D' or 'X' rating (contraindicated).

  1. Ethanol (toxic alcohols) - Category C
    • Reproduction studies have not been conducted with alcohol injection. Ethanol crosses the placenta, enters the fetal circulation, and has teratogenic effects in humans. When used as an antidote during the second or third trimester, Fetal Alcohol Syndrome AS is not likely to occur due to the short treatment period; use during the first trimester is controversial.
    • Alternative (preferred) antidote: fomepizole.
  2. Methylene blue (methemoglobinemia) - Category X
    • Use during amniocentesis has shown evidence of fetal abnormalities, but it has been used orally without similar adverse events. IV may be ok.
  3. Lorazepam and diazepam (seizures, nerve agents) - Category D
    • Teratogenic effects have been observed in some animal studies and in humans. Lorazepam/diazepam and their metabolite cross the human placenta.
  4. Potassium iodide (radioactive iodine) - Category D
    • Iodide crosses the placenta (may cause hypothyroidism and goiter in fetus/newborn). Use for protection against thyroid cancer secondary to radioactive iodine exposure is considered acceptable based upon risk:benefit, keeping in mind the dose and duration.
  5. Amyl nitrite (cyanide) - Category C (manufacturer contraindicates)
    • Animal reproduction studies have not been conducted. Because amyl nitrate significantly decreases systemic blood pressure and therefore blood flow to the fetus, use is contraindicated in pregnancy (per manufacturer).
    • Other options exist to treat cyanide exposure including sodium nitrite, sodium thiosulfate, and hydroxocobalamin.
  6. Penicillamine (chelator) - Category D

In most cases, the benefits of short-term use probably outweigh the risk, especially when accounting for the health and prognosis of the mother.


Lexi-Comp Online, Lexi-Drugs Online, Hudson, Ohio: Lexi-Comp, Inc.; February 14, 2013.

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