A 38-year-old woman in very early pregnancy has been treated with metronidazole for two weeks becau

Fråga: A 38-year-old woman in very early pregnancy has been treated with metronidazole for two weeks because of a genital infection. The drug exposition is estimated to have taken place immediately after conception. Is there a risk of teratogenicity?

Sammanfattning: There is no conclusive evidence that metronidazole causes an increased risk of teratogenicity when used during early pregnancy.

Svar: The question about the safety of metronidazole during pregnancy has been dealt with several times previously (1-3). Metronidazole is officially categorized in group B:2 concerning the use in pregnancy, ie the experience from use in pregnant women is limited but has so far not shown any negative effects. Animal data are incomplete but do not imply an increased risk of teratogenicity (4).

Animal and in vitro models have shown a carcinogenic or mutagenic potential (5-6), but these properties have not been shown in humans (6). Some investigations have found an increased risk of teratogenicity when the agent was used in early pregnancy (6-7), but the significance of these findings has been questioned (5,8,9) and the most extensive and thorough investigations are said to be negative (4). A renewed Medlinesearch has not revealed any more information. A discussion with the embryologist Professor Bengt Källen confirms the lack of conclusive positive evidence for teratogenicity (9). Furthermore, any toxic damage to the conception product in very early pregnancy would be likely to result in early spontaneous abortion or non-implantation (10). 1 Drugline nr 06664 (year 1989) 2 Drugline nr 07731 (year 1991) 3 Drugline nr 07695 (year 1990) 4 FASS 1992; page 337 5 Folb & Dukes, Drug safety in pregnancy. 1990; page 185-186, 195, 437 6 Briggs, Drugs in pregnancy and lactation. 1986; 2nd ed: 292-293 7 Cantu JM, Garcia-Cruz D: Midline facial defect as a teratogenic effect of metronidazole. Birth Defects 1982; 18: Pta 85-88 8 Läkemedelsboken 91/92. Apoteksbolaget, 1991; page 736 9 Personal communication, professor Bengt Källen, Department of Embryology, University of Lund 10 Farmakoterapeutiska principer vid val av läkemedel under graviditet. Terapikonferens 1983. Apoteksbolaget, Landstingsförbundet, Socialstyrelsens läkemedelsavdelning