Absorption, distribution and excretion of3H-labeled cephaeline- and emetine-spiked ipecac syrup in rats

The maximum plasma radioactivity levels of tritium (3H)-labeled cephaeline, (24.3, 28.7 and 40.6 ng eq./mL) were reached at 2.00-3.33 hours following oral dosing of ipecac syrup. The maximum plasma radioactivity levels of3H-emetine (2.71, 6.47 and 9.62 ng eq./mL) were reached at 1.08–2.33 hours following ipecac syrup administration. The Cmax values of3H-cephaeline were followed by a biexponential decrease with half-lives t1/2(λz) of 3.45–9.40 hours. On the other hand, the t1/2(λz) of3H-emetine were 65.4–163 hours, which revealed a biexponential decrease. The radioactivity of both tritium-labeled compounds was distributed maximally in most tissues at 24 hours. For3H-cephaeline, the maximum radioactivity levels in tissues were approximately 100–150 times greater than in plasma. For3H-emetine, the radioactivity levels in tissues were approximately 1000–3000 times greater than in plasma. Tissue radioactivity levels decreased at a substantially slower rate than that observed in plasma. Tissue radioactivity of3H-emetine decreased more slowly than that of3H-cephaeline. For3H-cephaeline, the cumulative biliary excretion of radioactivity was 57.5% at 48 hours. The cumulative urinary and fecal excretion of radioactivity in these rats was 16.5% and 29.1%, respectively, of the dose at 48 hours following dosing. For3H-emetine, the cumulative biliary excretion of radioactivity was 12.5% at 48 hours. The cumulative urinary and fecal excretion of radioactivity was 9.4% and 34.1%, respectively, of the administered dose at 48 hours. The radioactivity level of3H-emetine remaining in the carcasses at 48 hours was equivalent to approximately 50% of the dose. A portion of each tritium-labeled compound was subjected to entero-hepatic circulation. Thus, the absorption rate of3H-cephaeline and3H-emetine was estimated to be approximately 70% on the basis of the data obtained from excretion studies. There was no difference in the absorption process between these two compounds. However, the difference was admitted in the biliary clearance, which is the main excretion route of both compounds. Delayed excretion of3H-emetine may be primarily due to its resorption as related to entero-hepatic circulation and tissue retention. This study has determined the absorption, distribution and excretion of3H-cephaeline and3H-emetine in rats.