The embryotoxic effect on rabbits of monophenylbutazone (monazan) compared with phenylbutazone and thalidomide

Maternal toxicity: a possible etiological factor in embryo-fetal deaths and fetal malformations of rodent-rabbit species

Data from animal teratology studies were surveyed to determine whether embryo-fetal mortality and fetal malformations result from a primary action of the agent on the conceptus or if they are secondary to maternal toxicity--a consequence of administration with high dose levels of test chemicals. A fairly strong association between embryo-fetal mortality and maternal toxicity was revealed by analysis of data from hamsters, mice, rats, and rabbits in 234 studies of chemical and physical agents, of which 83 were conducted at both maternotoxic and nonmaternotoxic doses, 94 only at maternotoxic doses, and 49 at nonmaternotoxic doses. In the above studies, only nine chemicals (four each in hamsters and rabbits and one in rats) were reported to induce embryo-fetal deaths at apparently nonmaternotoxic doses. These findings tend to suggest a contributory role for maternal toxicity in the induction of embryo-fetal deaths. The previously reported hypothesis that certain fetal defects in mice may perhaps be caused by maternal toxicity was also found to be true in a review of data on hamsters, rats, and rabbits. Salient maternal toxicity-associated fetal malformations were exencephaly, encephalocele, micro- or anophalmia, and fused ribs in hamsters and defective (fused, missing, or extra) ribs, vertebrae, and sternebrae, ex-, an-, or microphthalmia, and cleft palate in rats and rabbits. These malformations occurred at low frequencies, generally with no readily apparent dose-response relationship. Presumptive evidence indicates that embryo-fetal deaths, and the above-mentioned fetal malformations in experimental animals, which in published literature are presently attributed to chemical induction for a large number of chemicals, may be a consequence of maternal toxicity per se.

Pharmacokinetics of [4-14C] mofebutazone after oral administration in man

The pharmacokinetics of mofebutazone was investigated in man after oral administration of [4-14C] mofebutazone in suspension form (7 mg/kg body weight). The blood concentration/time course was found to fit a two compartment open model with first order absorption (ka = 10.1 h-1) where elimination (kel = 0.304 h-1) occurs only from compartment 1. The maximum concentration was reached after 0.3 h in compartment 1 and after 2 h in compartment 2. Mofebutazone was found to be excreted almost exclusively via the kidney; 97% of the administered dose was found in urine already at 72 h. Excretion takes place very rapidly; 24% of the dose was excreted in 1.5 h and 45% in 3 h. 92% of the mofebutazone excreted was the conjugated form. Two glucuronides were detected in the 24 h urine; one of these seemed to be identical to a glucuronide fractionated from the urine of rat. The renal clearance of mofebutazone in man was found to be 3.38 l/h. The almost complete recovery of mofebutazone in the urine indicates that after oral administration, this drug has a very high bioavailability via the oral route.

Quantitative correspondence between the in vivo and in vitro activity of teratogenic agents

We have tested 74 teratogenic and 28 nonteratogenic agents in a recently developed in vitro teratogen assay system. The assay identifies teratogens by their ability to inhibit attachment of ascites tumor cells to plastic surfaces coated with concanavalin A. There is a qualitative agreement between in vivo animal data and in vitro activity for 81 of the 102 agents (79%). Quantitative analysis shows a highly significant correlation coefficient of 0.69 between the inhibitory in vitro dose and the lowest reported teratogenic dose for 54 of the 60 inhibitory teratogens. The doses analyzed ranged over 5 orders of magnitude. We interpret these results to mean that attachment inhibition in concert with other, complementary, in vitro assay systems can become a useful method for the assessment of the teratogenic potential of environmental agents.

Animal virus screens for potential teratogens. I. Poxvirus morphogenesis

The growth of poxvirions in cell culture is considered a teratogen screening test, since this virus has a rapid, simple morphogenetic pathway that is dependent upon cell proliferation. Vaccinia WR-infected BSC 40 monolayers were exposed to 42 known teratogens and 9 nonteratogens at dosages from 1 microM to 100 mM. After 24 h of infection, the number of functional virions was determined by plaque assay. Thirty-three of the 42 teratogens inhibited the virus, 3 teratogens stimulated the virus, and 6 teratogens were false-negatives. Eight of the 9 nonteratogens had no effect on virus proliferation at dosages as high as 600 times the lowest reported teratogenic dosage. The number of new virions could be directly related to the concentration of the teratogen in vitro, thus allowing each compound to be characterized by an RD50. The RD50 dosage in milligrams per liter was 98% correlated with the lowest reported teratogenic dose in vivo in milligrams per kilogram. In sum, vaccinia-infected cells have an easily identifiable endpoint, plaque-forming units, which may be an accurate prognosticator of teratogenesis.

Disposition of [4-14C]mofebutazone in the rat

The absorption and elimination of radioactivity after the oral or intraperitoneal administration of[4-14C]mofebutazone was studied in rats. The blood concentration of radioactivity reached a maximum after about 0.7 h, fell rapidly until about 2 h, and then declined slowly. There was sometimes a second peak between 3-6 h. Elimination of radioactivity in urine and feces was extensive and rapid. Over a 24 h period, 73% of the orally administered radioactivity was eliminated in the urine and 15% in the faeces; most of this was eliminated during the first 8 h (89% of the urine radioactivity, 56% of the faeces radioactivity). In anaesthetized rats with cannulated bile ducts, 94% of the intraperitoneally injected radioactivity was eliminated in the bile over a 6 h period. Most of the radioactivity (about 85%) eliminated in the bile and the urine was in the form of a glucuronide and only small amounts less than 10%, was in the form of mofebutazone.