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Chapter 182. Medications and Pregnancy

Imre Rédai, MD, FRCA

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FDA Classification of Medications during Pregnancy
Category AAdequate and well-controlled human studies have failed to demonstrate a risk to the fetus in the first trimester of pregnancy (and there is no evidence of risk in later trimesters)
Category B
  • Animal reproduction studies have failed to demonstrate a risk to the fetus and there are no adequate and well-controlled studies in pregnant women
  • Or
  • Animal studies have shown an adverse effect, but adequate and well- controlled studies in pregnant women have failed to demonstrate a risk to the fetus in any trimester
Category CAnimal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks
Category DThere is positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience or studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks
Category XStudies in animals or humans have demonstrated fetal abnormalities and/or there is positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience, and the risks involved in use of the drug in pregnant women clearly outweigh potential benefits
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Anesthetic Medications...
DosingFetal effects
Induction agents
  • Dosing requirements are unchanged or mildly reduced for ultrashort-acting barbiturates and propofol (10–15%)
  • Propofol TIVA: reduce dose by <10%
  • Equilibration with fetal tissues is rapid
  • Fetal elimination strongly depends on reverse diffusion to mother
  • Intravenous induction agents reduce fetal heart rate variability
Narcotics
  • Endogenous endorphin production reduces exogenous opioid requirement
  • Peripartum oxytocin release has been implicated in reduced narcotic requirements
  • Remifentanil has the shortest half-life in the newborn and has become a popular agent for labor analgesia when a neuraxial technique is contraindicated (usual starting dose is 0.03 μg/kg/min increased as needed to 0.1 μg/kg/min)
  • Narcotics reduce fetal heart rate variability
  • Short-acting rapid-onset opioids have been reported to cause fetal bradycardia
  • Intrathecal narcotic requirements are reduced by 30–50% when compared with nonpregnant patients
  • There are no clear data for IV narcotic dose reduction
Sedatives
  • Benzodiazepines are traditionally avoided in pregnant patients
  • Dexmedetomidine has been reported for labor analgesia (insufficient data for assessment of safety of drug)
Muscle relaxants
  • Sensitivity to muscle relaxants is unchanged
  • Pseudocholinesterase activity is reduced by 30% in the pregnant patient; this has no effect on the onset and duration of succinylcholine
  • NMBs do not cross the placenta in significant amounts
  • Magnesium sulfate therapy may increase sensitivity to nondepolarizing NMB (no effect on succinylcholine)
Neuromuscular reversal agentsDosing requirements are unchanged
  • Neostigmine and glycopyrrolate do not cross the placenta
  • Atropine crosses the placenta
Volatile anestheticsMAC reduced by 30%Volatile anesthetics reduce fetal heart rate variability
Local anestheticsNerves are more sensitive to local anesthetic effect (faster block onset)

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