METHICILLIN

Fetal Risk Summary

Methicillin is a penicillin antibiotic (see also Penicillin G). The drug rapidly crosses the placenta into the fetal circulation and amniotic fluid (1,2). Following a 500-mg IV dose over 10–15 minutes, peak levels of 13.0 and 10.5 µg/mL were measured in maternal and fetal serums, respectively, at 30 minutes (1). Equilibration occurred between the two serums within 1 hour. No effects were reported in the infants.

No reports linking the use of methicillin with congenital defects have been located. The Collaborative Perinatal Project monitored 50,282 mother-child pairs, 3,546 of which had 1st trimester exposure to penicillin derivatives (3, pp. 297–313). For use anytime during pregnancy, 7,171 exposures were recorded (3, p. 435). In neither group was evidence found to suggest a relationship to large categories of major or minor malformations or to individual defects.

Breast Feeding Summary

No data are available (see Penicillin G).

References

1. Depp R, Kind A, Kirby W, Johnson W. Transplacental passage of methicillin and dicloxacillin into the fetus and amniotic fluid. Am J Obstet Gynecol 1970;107:1054–7.
2. MacAulay M, Molloy W, Charles D. Placental transfer of methicillin. Am J Obstet Gynecol 1973;115:58–65.
3. Heinonen OP, Slone D, Shapiro S. Birth Defects and Drugs in Pregnancy. Littleton, MA: Publishing Sciences Group, 1977.