Two cases of acetaminophen overdose in late pregnancy have been reported. In both cases neither the neonate nor the mother suffered hepatic toxicity.

Investigations have revealed conflicting results with regards to the pharmacokinetic disposition of acetaminophen in pregnant women. One study has suggested that the oral clearance of acetaminophen is 58% higher and the elimination half-life is 28% lower in pregnant women compared to non-pregnant women. Another study has suggested that the elimination half-life is not different in patients who are pregnant. That study also suggested that the volume of distribution of acetaminophen may be higher in pregnant women.

One study has suggested that acetaminophen in typical oral doses may result in a reduced production of prostacyclin in pregnant women. That study has also suggested that acetaminophen does not affect thromboxane production.

In most cases of congenital malformations in infants exposed to propoxyphene, other drugs were also used during pregnancy and a clear association between propoxyphene use and the malformations has not been established. Some of the specific malformations described in case reports of infants exposed to propoxyphene (and often other drugs) have included: prune perineum, Pierre Robin syndrome, arthrogryposis, severe caudal dysplasia, micrognathia, microcephaly, ductus arteriosus persistens, cataract, benign tumors, club foot, and limb reduction defects.

The Collaborative Perinatal Project identified 686 mother-child pairs with first trimester exposure to propoxyphene and observed 31 malformed children. (In that group, 34.4 malformed children were expected.)

A study of Michigan Medicaid patients identified 1029 neonates exposed in utero to propoxyphene and observed 41 malformed children (personal communication, Franz Rosa, MD, Food and Drug Administration, 1994). (In that group, 43 malformed children were expected.)

Neonatal propoxyphene withdrawal symptoms include irritability, hypertonicity, jitteriness, increased temperature, tremors, increased appetite, diarrhea and high-pitched cry.

Acetaminophen has not been formally assigned to a pregnancy category by the FDA. Acetaminophen is routinely used for short-term pain relief and as an antipyretic in all stages of pregnancy. Acetaminophen is believed to be safe in pregnancy when used intermittently for short durations. Acetaminophen should only be given during pregnancy when need has been clearly established.

Propoxyphene has not been formally assigned to a pregnancy category by the FDA. Several case reports have described infants exposed to propoxyphene in utero who were born with a variety of congenital malformations. Withdrawal symptoms have also been reported in neonates whose mothers took propoxyphene during pregnancy. There are no controlled data in human pregnancy. Propoxyphene is only recommended for use during pregnancy when benefit outweighs risk.

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