It has been shown that the analgesic and cyclooxygenase inhibitor activity of ketorolac tromethamine (KT), which is marketed as the racemic mixture of (-)S and (+)R enantiomers, resides primarily with (-)S ketorolac and that the ulcerogenic activity of this agent also resides in (-)S ketorolac. Resolution of individual enantiomers for analysis in plasma samples has been accomplished by two methods: derivatization to form diastereomers that are separated by HPLC, or direct HPLC using a chiral phase column. When mice and rats were given oral solutions of (-)S and (+) KT, it was found that the kinetics and interconversion of the enantiomers were species and dose dependent. Interconversion was higher in mice than in rats; when (-)S KT was administered, 71% of the area under the concentration-time curve (AUC) was due to (+)R ketorolac in mice, compared with 12% in rats. More interconversion was observed at higher doses; the percent of AUC due to (-)S ketorolac when (+)R KT was administered increased from 12% to 25% in mice and from 2% to 8% in rats. In general, more interconversion occurred from (-)S to (+)R ketorolac in the animal studies. Human subjects were given single oral solution doses of racemic KT (30 mg), (-)S KT (15 mg), and (+)R KT (15 mg). The plasma concentrations of (-)S ketorolac were lower than (+)R ketorolac at all sample times after racemic KT (22% of the AUC was due to (-)S ketorolac). When (+)R KT was administered, (-)S ketorolac was not detectable and interconversion was essentially 0%. When (-)S KT was administered, significant levels of (+)R ketorolac were detectable and interconversion was 6.5%. After all doses, plasma half-life was shorter and clearance greater for (-)S ketorolac than for (+)R ketorolac. Thus, in humans very little or no interconversion of (+)R to (-)S was observed, and interconversion of (-)S to (+)R was minimal (6.5%). These data demonstrate that the kinetics and interconversion of the enantiomers of ketorolac is different in animals and humans as well as from most other NSAIDs. This may be due to more rapid excretion or metabolism of (-)S ketorolac and a different mechanism of interconversion.
The Fischer 344 rat is being used increasingly in toxicology studies. There have been few reports in which rats of this strain were used in teratology and reproduction studies, but comparison of teratologic data with other toxic and points and kinetic information would be greatly facilitated by using the same strain. Therefore, the embryotoxic effects of two positive teratogens, aspirin and hydroxyurea, were compared in Fischer rats and in the commonly used Wistar rats. Aspirin was administered in single oral doses of 500 and 625 mg/kg on d 10; hydroxyurea was injected ip at 500 mg/kg on d 11. Dams were sacrificed on d 20 and fetuses examined for skeletal and visceral defects. Male and female fetal weights and lengths were significantly reduced in treated groups in both strains. Both teratogens caused a significant increase in resorptions in Wistar and Fischer rats. A wide variety of skeletal alterations were induced by both teratogens in both strains. These included extra ribs, fused or missing ribs, extra thoracic and lumbar vertebrae, split vertebral centra, and missing vertebrae. Only a small number of Fischer fetuses exhibited visceral malformations such as hydrocephaly and cleft palate. The frequency of soft-tissue malformations, including cleft palate and severe cardiac anomalies, was much higher in Wistar fetuses.
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