DICLOXACILLIN

Fetal Risk Summary

Dicloxacillin is a penicillin antibiotic (see also Penicillin G). The drug crosses the placenta into the fetal circulation and amniotic fluid. Levels are low compared to other penicillins due to the high degree of maternal protein binding (1,2). Following a 500-mg IV dose, the fetal peak serum level of 3.4 µg/mL occurred at 2 hours (8% of maternal peak) (2). A peak of 1.8 µg/mL was obtained at 6 hours in the amniotic fluid.

No reports linking the use of dicloxacillin 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 in pregnancy, 7,171 exposures were recorded (3, p. 435). In neither case was evidence found to suggest a relationship to large categories of major or minor malformations or to individual defects.

In a surveilance study of Michigan Medicaid recipients involving 229,101 completed pregnancies conducted between 1985 and 1992, 46 newborns had been exposed to dicloxacillin during the 1st trimester (F. Rosa, personal communication, FDA, 1993). One (2.2%) major birth defect was observed (two expected). No anomalies were observed in six defect categories (cardiovascular defects, oral clefts, spina bifida, polydactyly, limb reduction defects, and hypospadias) for which specific data were available. Although the number of exposures is small, these data do not support an association between the drug and congenital defects.

Breast Feeding Summary

No reports describing the use of dicloxacillin during lactation have been located. Because other penicillins are excreted in breast milk in low concentrations (e.g., see Ampicillin and Penicillin G), the presence of dicloxacillin should also be expected. Although adverse effects from other penicillins in breast milk are rare, three potential problems exist for the nursing infant: modification of bowel flora, direct effects on the infant (e.g., allergic response), and interference with the interpretation of culture results if a fever workup is required.

References

1. MacAulay M, Berg S, Charles D. Placental transfer of dicloxacillin at term. Am J Obstet Gynecol 1968;102:1162–8.
2. 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.
3. Heinonen OP, Slone D, Shapiro S. Birth Defects and Drugs in Pregnancy. Littleton, MA:Publishing Sciences Group, 1977.