Robenidine

The worldwide usage of polyether antibiotics for controlling coccidiosis is approximately 190 million compared to a total market of 210—220 million. Monensin and salinomycin represent about 65—70% of this market lasalocid, narasin, and maduramicin make up the remainder. Other compounds for coccidiosis control include nicarbazine, halofiinginone, amprolium, and robenidine. Worldwide usage is in excess of 3 million kg of product. 

Robenidine hydrochloride labeled with carbon-14 in the amino guanidine carbon atom had a specific activity of 18.61 pCi/mg. 

To obtain excreta for this study, a turkey was fed 250 grams of a basal diet containing 66 ppm robenidine hydrochloride for ten days. On the eleventh day, the turkey was dosed with 17 mg or 316.37 pCi of carbon-lA robenidine in a capsule. 

The total radioactivity applied to the soil as carbon-lA robenidine residues in excreta was 167.5A microcuries. For Tank B, 100 microcuries of carbon-1A DDT and 9 mg of unlabeled DDT were mixed in a ball mill with 2.5 kg of soil and 52g of control turkey excreta. The amount of DDT added to the soil corresponded to an application rate of approximately 1.5 lbs/acre. For Tank C, control turkey excreta was mixed with the top two inches of soil as previously described. 

Approximately 60% of the carbon-14 robenidine administered to the turkey was recovered in the excreta within 48 hours. 

About 84% of the radioactivity in the excreta was extracted with methanol, another 9% was extracted with a 1% hydrochloric acid/ methanol mixture leaving about 7% unextracted. It was found by TLC that 75% of the methanol-soluble radioactivity was due to the presence of unchanged robenidine (Figure 3). Metabolites 1, 2, and 3 accounted for 7, 2 and 0.7% of the extractable radioactivity, respectively. 

Sorghum seedlings radioassayed for carbon-14 residues at the time of larval feeding showed low levels of 0.004 and 0.013 ppm for carbon-14 DDT and carbon-14 robenidine, respectively. 

Residue levels of carbon-14 in water were low, especially in the case of carbon-14 DDT, indicating that DDT-related residues remain bound to the soil (Figure 4). After an initial concentration of 0.009 ppb at Day 1, the concentration of carbon-14 DDT residues reached an equilibrium of about 0.02 ppb by the third day and then dropped off slightly to 0.012 to 0.013 ppb at the time the mosquito larvae and fish were introduced. Carbon-14 residues in water derived from carbon-14 robenidine showed an initial concentration of 0.344 ppb and then remained fairly constant at about 1 ppb throughout the study, indicating that robenidine-related residues are polar in nature and readily migrate into the water phase and reach equilibrium very rapidly. 

Thin-layer chromatography of the water from the carbon-14 robenidine study showed about 12% (0.138 ppb) parent compound,... 

About 20% of the radioactivity in the soil from the carbon-14 robenidine tank was extractable at the end of the experiment with 80% remaining unextractable. Chromatography of the extract-able radioactivity showed extensive degradation of the compound as shown in Figure 7. 

Robenidine, which was the major component in the excreta, represented about 10% of the extractable radioactivity in the soil. In terms of total carbon-14 residues in the soil, parent compound represented 2.0%. Metabolite 2, which was present only in trace quantities in the excreta, accounted for 21% of the extractable radioactivity or 4.2% of the total carbon-14 residues in the soil. This metabolite was also the only significant compound found in the water. Three other metabolites accounted for about 18% of the extractable radioactivity in the soil, namely, Metabolite 3, 5.3%, Metabolite 6, 7.6% and Metabolite 10, 4.9%. Polar material which was not resolved from the origin represented 25% of the extractable radioactivity in the soil. 

In the fish, the last element in the food chain web, methanol extracted about 58% of the radioactivity resulting from the carbon-14 robenidine treatment leaving 42% unextracted, indicating that robenidine was being extensively degraded by fish into very polar nonextractable products. 

Thin-layer chromatography of the extractable radioactivity did not show any parent compound even though robenidine was one of the components in the environment (water) (Figure 8). 

Figure 7. TLC of the methanol-soluble radiactivity in the aged soil/excreta mixture from the 14C-robenidine model ecosystem...

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