OXACILLIN

Fetal Risk Summary

Oxacillin is a penicillin antibiotic (see also Penicillin G). The drug crosses the placenta in low concentrations. Cord serum and amniotic fluid levels were less than 0.3 µg/mL in 15 of 18 patients given 500 mg orally 0.5–4 hours before cesarean section (1). No effects were seen in the infants.

The Collaborative Perinatal Project monitored 50,282 mother-child pairs, 3,546 of which had 1st-trimester exposure to penicillin derivatives (2, pp. 297–313). For use anytime during pregnancy, 7,171 exposures were recorded (2, p. 435). In neither group was evidence found to suggest a relationship to large categories of major or minor malformations or to individual defects.

A 1999 study used the population-based data-set of the Hungarian Case-Control Surveillance of Congenital Abnormalities (1980–1996) to evaluate the teratogenicity of oxacillin (3). The data base contained 22,865 fetuses or newborns with congenital malformations and 38,151 matched control newborns without birth defects. The mothers of 14 cases (4 in the 1st trimester) and 19 controls (8 in the 1st trimester) were treated with oxacillin during pregnancy. No associations were discovered based on a comparison with the expected rates in 24 congenital anomaly groups (3).

An interaction between oxacillin and oral contraceptives resulting in pregnancy has been reported (4). Other penicillins (e.g., see Ampicillin) have been suspected of this interaction, but not all investigators believe it occurs. Although controversial, an alternate means of contraception may be a practical solution if both drugs are consumed at the same time.

Breast Feeding Summary

Oxacillin is excreted in breast milk in low concentrations (1). Although no adverse effects have been reported, 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. Prigot A, Froix C, Rubin E. Absorption, diffusion, and excretion of new penicillin, oxacillin. Antimicrob Agents Chemother 1962:402–10.
2. Heinonen OP, Slone D, Shapiro S. Birth Defects and Drugs in Pregnancy. Littleton, MA: Publishing Sciences Group, 1977.
3. Czeizel AE, Rockenbauer M, Sorensen HT, Olsen J. Teratogenic evaluation of oxacillin. Scan J Infect Dis 1999;31:311–2.
4. Silber TJ. Apparent oral contraceptive failure associated with antibiotic administration. J Adolesc Health Care 1983;4:287–9.