Amoxicillin Risk Summary

Fetal Risk Summary

Amoxicillin is a penicillin antibiotic similar to ampicillin (see also Ampicillin). No reports linking its use to congenital defects have been located.

Reproduction studies have been conducted in mice and rats at doses up to 10 times the human dose (1). No effect on fertility or fetal harm was observed at this dose.

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. Amoxicillin has been used as a single 3-g dose to treat bacteriuria in pregnancy without causing fetal harm (3,4).

In a surveillance study of Michigan Medicaid recipients involving 229,101 completed pregnancies conducted between 1985 and 1992, 8,538 newborns had been exposed to amoxicillin during the 1st trimester (F. Rosa, personal communication, FDA, 1993). A total of 317 (3.7%) major birth defects were observed (363 expected). Specific data were available for six defect categories, including (observed/expected) 76/85 cardiovascular defects, 16/14 oral clefts, 6/7 spina bifida, 17/24 polydactyly, 9/16 limb reduction defects, and 22/22 hypospadias. These data do not support an association between the drug and the defects.

Amoxicillin depresses both plasma-bound and urinary excreted estriol (see also Ampicillin) (5). Urinary estriol was formerly used to assess the condition of the fetoplacental unit, but this is now done by measuring plasma unconjugated estriol, which is not usually affected by amoxicillin.

Breast Feeding Summary

Amoxicillin is excreted into breast milk in low concentrations. Following a 1-g oral dose given to six mothers, peak milk levels occurred at 4-5 hours, averaging 0.9 g/mL (range 0.681.3 g/mL) (6). Mean milk:plasma ratios at 1, 2, and 3 hours were 0.014, 0.013, and 0.043, respectively. Although no adverse effects have been observed, three potential problems exist for the nursing infant: modification of bowel flora, direct effects on the infant (e.g., allergy or sensitization), and interference with the interpretation of culture results if a fever workup is required. The American Academy of Pediatrics considers amoxicillin to be compatible with breast feeding (7).

References

1. Product information. Amoxil. SmithKline Beecham Pharmaceuticals, 2000.
2. Heinonen OP, Slone D, Shapiro S. Birth Defects and Drugs in Pregnancy. Littleton, MA:Publishing Sciences Group, 1977.
3. Masterton RG, Evans DC, Strike PW. Single-dose amoxicillin in the treatment of bacteriuria in pregnancy and the puerperium-a controlled clinical trial. Br J Obstet Gynaecol 1985;92:498505.
4. Jakobi P, Neiger R, Merzbach D, Paldi E. Single-dose antimicrobial therapy in the treatment of asymptomatic bacteriuria in pregnancy. Am J Obstet Gynecol 1987;156:114852.
5. Van Look PFA, Top-Huisman M, Gnodde HP. Effect of ampicillin or amoxicillin administration on plasma and urinary estrogen levels during normal pregnancy. Eur J Obstet Gynaecol Reprod Biol 1981;12:22533.
6. Kafetzis D, Siafas C, Georgakopoulos P, Papadatos C. Passage of cephalosporins and amoxicillin into the breast milk. Acta Paediatr Scand 1981;70:2858.
7. Committee on Drugs, American Academy of Pediatrics. The transfer of drugs and other chemicals into human milk. Pediatrics 1994;93:13750.

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