Analysis of the nonsteroidal anti-inflammatory drug literature for potential developmental toxicity in rats and rabbits

BACKGROUND: Nonsteroidal anti‐inflammatory drugs (NSAIDs) are among the most commonly prescribed to pregnant women. Some case‐control studies have linked the NSAIDs aspirin and indomethacin with a risk of congenital abnormalities and low birthweight. High doses of aspirin produce developmental toxicity in rats (e.g., gastroschisis/umbilical hernia, diaphragmatic hernia [DH]) when administered during sensitive windows of development. Unlike other NSAIDs, aspirin irreversibly inhibits cyclooxygenases (COXs) 1 and 2. Hence, the developmental toxicity seen in rats after exposure to aspirin may be due to the irreversible inhibition of COX‐1 and/or COX‐2. If so, other NSAIDs, which act through a reversible inhibition of COX, may produce a weak developmental toxicity signal or no developmental toxicity signal when tested in preclinical models. To investigate this relationship, a comprehensive analysis of the NSAID developmental toxicity literature was undertaken to determine whether NSAIDs other than aspirin induce developmental anomalies similar to those elicited by aspirin. METHODS: Developmental toxicity studies were identified through literature searches of PubMed and TOXNET, and pregnancy outcome data were extracted and tabulated. By using a set of defined criteria, each study was evaluated for quality and assigned to one of five tiers. The relation between certain malformations and NSAID treatment was analyzed for the best studies (tiers 1–4) by using concurrent control data (Mantel–Haenszel and permutation tests) and by combining the concurrent control data with historical control data (χ² test and permutation tests). RESULTS: A qualitative analysis of these data led to a focus on three types of malformations: DH, ventricular septal defects (VSDs), and midline defects (MDs). In rats, the incidences of VSD and MD were increased among fetuses treated with NSAIDs when compared with the concurrent controls. The extent of the increase was attenuated when the data from the aspirin studies were excluded from the analysis. There were no qualifying (i.e., tiers 1–4) aspirin studies conducted in rabbits, but the incidences of the three defects were increased over control incidences among non‐aspirin NSAID‐treated animals. Statistical analysis of these data was subsequently conducted. When tiers 1–4 were combined and compared with concurrent controls plus the most appropriate historical control database, the strongest associations were between NSAID treatment and VSD in rats, VSD in rabbits, and MD in rabbits. There also was some suggestion of an association between NSAID treatment and DH in rabbits. CONCLUSIONS: This analysis of the non‐clinical NSAID literature demonstrated a possible association between exposure to NSAIDs and developmental anomalies. The anomalies were similar for aspirin and for other NSAIDs, but effects occurred at a much lower incidence with non‐aspirin NSAIDs than previously reported with aspirin. Such a finding is consistent with the concept that reversible inhibition of COX‐1 and/or COX‐2 by other NSAIDs would produce weaker developmental toxicity signals than aspirin. However, there were limitations of the evaluated studies: (1) there were very few robust International Conference on Harmonization–compliant studies conducted with NSAIDs in the published literature; (2) many of the studies were conducted at doses well below the maximum tolerated dose (MTD), where effects are rarely seen; and (3) numerous studies were conducted above the MTD, where reduced numbers of fetuses hampered detection of low‐incidence findings. Although weak associations were observed, these limitations prevented us from definitively determining the presence or absence of a developmental toxicity signal from the existing body of NSAID data. Further exploration of this hypothesis will require assessing the potential association in animal models by using dose levels centered around the MTD. Birth Defects Research (Part B) 68:5–26, 2003. © 2003 Wiley‐Liss, Inc.     

Relationship between cyclooxygenase 1 and 2 selective inhibitors and fetal development when administered to rats and rabbits during the sensitive periods for heart development and midline closure

BACKGROUND: A review of the scientific literature suggested the occurrence of low‐level incidences of ventricular septal defect (VSD) and midline defect (MD) in rat fetuses and diaphragmatic hernia (DH), VSD, and MD in rabbit fetuses after maternal exposure to nonsteroidal anti‐inflammatory drugs (NSAIDs). Aspirin, an NSAID that irreversibly inhibits cyclooxygenase 1 (COX‐1) and COX‐2, induces DH, VSD, and MD when administered as one dose during the sensitive periods of development in rats. Unlike aspirin, other NSAIDs, including selective COX‐2 inhibitors, reversibly inhibit COX activity. To evaluate whether the dysmorphogenesis observed after maternal NSAID exposure correlates with COX‐1 or COX‐2 inhibition, a series of compounds with different capacities to inhibit COX‐1 and COX‐2 were administered to pregnant rats and rabbits during the sensitive period for heart development and midline closure. METHODS: The compounds selected, ranked from the most COX‐2 selective to the most COX‐1 selective based on COX inhibition in a human whole blood assay, were CJ‐19,209, meloxicam, diclofenac, diflunisal, ibuprofen, and ketorolac. Rat dams were treated on gestation days (GDs) 9 and 10, and rabbit does were treated on GDs 9, 10, and 11. The doses selected for evaluation represented the maximum tolerable dose for the compound, with the exception of CJ‐19,209, which was dosed at 1000 mg/kg. Fetuses were collected by cesarean section on GDs 21 and 29 for rats and rabbits, respectively, and all fetuses were examined for external and visceral developmental anomalies. RESULTS: In rabbits, diflunisal induced DH, VSD, and MD (omphalocele) and single incidences of VSD and MD (gastroschisis) were noted in the ibuprofen group; no other developmental findings were associated with treatment. In rats, ibuprofen, diflunisal, and ketorolac induced increases in the incidence of VSD. In general, the induction of developmental defects was associated with compounds that selectively inhibit COX‐1 or have a high ratio of COX‐1 to COX‐2 inhibition. CONCLUSIONS: Inhibition of COX‐1 may be involved in the disruption of heart development, whereas the selective inhibition of COX‐2 (as assessed with CJ‐19,209) appears to have no effect on heart development and midline closure in rats and rabbits. Birth Defects Research (Part B) 68:47–56, 2003. © 2003 Wiley‐Liss, Inc.     

Developmental toxicity evaluation of 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) in Wistar rats

3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) is a genotoxic chlorination by-product in drinking water. There is some evidence that it has developmental toxic effects in vitro but its potential to cause developmental effects in vivo is not known. The developmental effects were evaluated in Wistar rats. Rats (22-26 dams per dose group) were administered MX by gavage at the dose levels of 3, 30, or 60 mg/kg in water on gestation days 6-19. Control animals received plain water. Clinical signs, body weight, and food and water consumption were recorded for the dams. On gestation day 20, a cesarean section was performed and the ovaries anduterine contents of the dams were examined and the liver, kidneys, spleen, and thyroid glands weighed. The fetuses of all dose groups were weighed, sexed, and observed for external and skeletal malformations and the fetuses of the two highest dose groups were evaluated for visceral malformations. The highest dose, 60 mg/kg of MX, was slightly toxic to the dams. It decreased the corrected body weight gain of dams by 32% and the water consumption by 16-17%. Kidney and liver weights were slightly increased. MX did not affect the number of implantations nor did it cause any resorptions. The body weights of fetuses were not significantly affected. MX did not cause external malformations or skeletal anomalies. Two fetuses at 60 mg/kg and one fetus at 30 mg/kg had major visceral malformations (persistent truncus arteriosus, diaphragmatic hernia, dilated aorta with a stenosis of pulmonary arteries) and two minor artery abnormalities were observed in those animals. The frequency of unilateral displaced testis was slightly higher (9.2%) in the 60-mg/kg dose group than in controls (1.6%). Since the abnormalities did not form a consistent pattern and occurred most at maternally toxic dose, we conclude that MX can be regarded as non-teratogenic.     

Developmental toxicity studies in Crl:CD (SD) rats following inhalation exposure to trichloroethylene and perchloroethylene

The potential for trichloroethylene (TCE) and perchloroethylene (PERC) to induce developmental toxicity was investigated in Crl:CD (SD) rats whole-body exposed to target concentrations of 0, 50, 150 or 600 ppm TCE or 0, 75, 250 or 600 ppm PERC for six hours/day, seven days/week on gestation day (GD) 6-20 and 6-19, respectively. Actual chamber concentrations were essentially identical to target with the exception of the low PERC exposure level, which was 65 ppm. The highest exposure levels exceeded the limit concentration (2 mg/L) specified in the applicable test guidelines. Maternal necropsies were performed the day following the last exposure. Dams exposed to 600 ppm TCE exhibited maternal toxicity, as evidenced by decreased body weight gain (22% less than control) during GD 6-9. There were no maternal effects at 50 or 150 ppm TCE and no indications of developmental toxicity (including heart defects or other terata) at any exposure level tested. Therefore, the TCE NOEC for maternal toxicity was 150 ppm, whereas the embryo/fetal NOEC was 600 ppm. Maternal responses to PERC were limited to slight, but statistically significant reductions in body weight gain and feed consumption during the first 3 days of exposure to 600 ppm, resulting in a maternal NOEC of 250 ppm. Developmental effects at 600 ppm consisted of reduced gravid uterus, placental and fetal body weights, and decreased ossification of thoracic vertebral centra. Developmental effects at 250 ppm were of minimal toxicological significance, being limited to minor decreases in fetal and placental weight. There were no developmental effects at 65 ppm.