Effect of microsampling method on toxicity evaluation of azathioprine in repeated dose toxicity studies in rats

<p>The microsampling (MS) method is a useful technique that can evaluate the toxicity and toxicokinetics (TK) of the test substance in the same individual and contribute to the reduction of the number of animals used in rodent safety studies; however, blood sampling with the MS method may affect the examination items of the immune system. Therefore, we investigated the effect of the MS method on toxicity evaluation using an immunotoxic substance azathioprine.</p><p>Six-week-olds Crl:CD (SD) rats were divided into an MS group in which blood was collected from the subclavian vein by the MS method and a non-blood sampling group. Azathioprine was administered orally to each group at doses of 0, 3, and 10 mg/kg/day for 4 weeks (n=5/dose). FiftyμL/point of blood sampling for TK analysis was performed at 6 and 7 points on Days 1 and 28, respectively. On Day 30 (the day after blood sampling at 24 hours after the final dosing), hematology and blood chemistry tests, organ weight measurement, and pathological examination were performed. The results obtained from the MS group and non-blood sampling group were compared.</p><p>Common changes between the MS group and non-blood sampling group by azathioprine were low values of WBC, lymphocyte, eosinophil, and monocyte, small thymus, and decrease lymphocyte in thymic cortex. In addition, no significant differences were observed among the any doses in each group, and there were no effects on the blood sampling of MS method. From the above, it was considered that MS method could be used to evaluate the examination items about the immune system properly.</p>