Placental anomalies and fetal loss in mice, after administration of doxycycline in food for tet-system activation.

During the course of a study aiming to obtain a tetracycline (Tet)-inducible transgene expression restricted to the placenta, we have observed a toxicity of doxycycline (dox) given in the food at doses of 2.5-10 mg/g to pregnant mice from two different inbred strains. During the second half of gestation, dox-fed non-transgenic mice presented placental anomalies and impaired fetal development proportional to the dose of antibiotic. Thus, dox administered in commonly used food doses can have an adverse effect on pregnancy. These observations are important for studies of placental or fetal development using inducible gene promoters.