AMBENONIUM

Fetal Risk Summary

Ambenonium is a quaternary ammonium chloride with anticholinesterase activity used in the treatment of myasthenia gravis. It has been used in pregnancy, but too little information is available to analyze (1,2 and 3). In one case, the mother took ambenonium (60 mg/day), pyridostigmine (420 mg/day), and neostigmine (105 mg/day) throughout gestation without apparent fetal harm (3).

Although it is ionized at physiologic pH, the molecular weight (about 609) is low enough that the nonionized fraction of ambenonium should cross the placenta to the fetus.

Some authors have cautioned that IV anticholinesterases should not be used in pregnancy because of the potential for inducing premature labor (1). Transient muscular weakness has been observed in about 20% of newborns of mothers with myasthenia gravis. The neonatal myasthenia is caused by transplacental passage of antiacetylcholine receptor immunoglobulin G antibodies (see Pyridostigmine).

Breast Feeding Summary

Although ambenonium is ionized at physiologic pH, the molecular weight (about 609) is low enough that excretion of the nonionized fraction into breast milk should occur. The amount of drug in milk, however, is probably small (4). The effect, if any, on a nursing infant from exposure to ambenonium from milk is unknown.

References

1. McNall PG, Jafarnia MR. Management of myasthenia gravis in the obstetrical patient. Am J Obstet Gynecol 1965;92:518–25.
2. Heinonen OP, Slone D, Shapiro S. Birth Defects and Drugs in Pregnancy. Littleton, MA:Publishing Sciences Group, 1977:345–56.
3. Lefvert AK, Osterman PO. Newborn infants to myasthenic mothers: a clinical study and an investigation of acetylcholine receptor antibodies in 17 children. Neurology 1983;33:133–8.
4. Wilson JT. Pharmacokinetics of drug excretion. In Wilson JT, ed. Drugs in Breast Milk. Australia (Balgowlah):ADIS Press, 1981:17.