Effects of serial cervical or tail blood sampling on toxicity and toxicokinetic evaluation in rats

Abstract

To assess the influences of blood sampling volumes or sites on toxicological and toxicokinetic (TK) evaluations, 4-week duration animal studies and a single-dose TK study of imipramine were conducted. In the toxicological evaluation, six-week-old Sprague-Dawley rats were divided into no blood and blood sampling groups. Fifty microliters (microsampling) or 100 μL (larger sampling) of blood/time point was collected from the jugular vein (50 μL of data was reported previously as Yokoyama et al., 2020) or the tail vein 6 to 7 times on days 1/2 and in week 4. Although no parameters were affected by the 100 μL sample from the tail vein, the 100 μL jugular vein sampling decreased the red blood cell parameters in females, possibly due to hemorrhage at the sampling site. Regarding the TK assessment, 50 μL of blood/site/time point was collected at 6 time points from the tail and jugular vein of the same male rats after single oral administration of 10 or 100 mg/kg imipramine, which was selected as a representative drug with high distribution volume. Although there were no differences in the AUC 0-24hr and C max values between the sites, the plasma concentrations at the early time points were significantly lower from the tail vein than the jugular vein. From our studies, 50 μL of jugular and tail vein microsampling did not affect the toxicity parameters or AUC/C max . However, appropriate toxicity considerations and/or selection of the blood sampling site may be important in the case of larger sampling volumes or blood concentration assessment.

Impact of microsampling on toxicological evaluation in rodent safety studies

“…When microsampling is performed from the jugular vein, effects on the site of blood collection are sometimes inevitable. In fact, hemorrhage lesions were observed subcutaneously in the neck of all rats and in the thoracic cavity of a female, which were related to the blood sampling site (Hattori et al, 2020). The cause of the hematological parameter changes was assumed by the authors to be caused by further blood loss at the local sampling site in addition to the volume of actual blood collected from the jugular vein since no degenerative changes in the hematopoietic organs were observed in the histopathological examination.…”

“…Similarly, assuming a typical 4‐week general toxicity study (Exp 1) in rats, serial blood sampling was performed on Days 1 to 2 and 27 to 28 from the jugular vein (Hattori et al, 2020). Blood sampling volume was 6 or 7 × 100 μl.…”

“…It has been reported that TK parameters including the area under the concentration‐time curve (AUC) differ between the caudal and orbital venous plexus (Hui et al, 2007; Korfmacher et al, 2015), especially for drugs with relatively large partition coefficients (e.g., fluoxetine). A comparative analysis of TK parameters between blood collection sites of jugular vein and tail vein, commonly used microsampling site in Japan and Europe/United States, respectively, was performed for imipramine, which has a large volume of distribution and distribution coefficient as a model drug (Hattori et al, 2020). The results showed no significant differences in AUC 0‐24h and maximum concentration (C max ) values between the two blood collection sites.…”

“…Blood sampling from the tail vein would be superior in terms of the effect on the erythrocytic parameters due to its less invasive nature. When blood is collected from animals that do not receive drugs, such as the control group, there is no toxicological effect of microsampling when the tail vein is selected as the blood collection site with a collection volume less than about 5% of the circulating blood volume within 24 h before the evaluation test (Hattori et al, 2020). On the other hand, if the blood collection volume is more than 5% of the circulating blood volume, anemia tendency and influences on other test parameters are noted (Caron et al, 2015; Powles‐Glover, Kirk, Wilkinson, et al, 2014).…”

Effect of microsampling (50 μL) on toxicological evaluation of methapyrilene, a hepatotoxic substance, in a collaborative 28-day study in female rats

“…Therefore, our team has performed several evaluation studies for the effects of microsampling on toxicological parameters or TK parameters using the rat model. It has been demonstrated that microsampling from the jugular vein and tail vein shows low concern for preventing evaluation in typical toxicity studies, that there is no marked influence on toxicity parameters between blood sampling sites; this is a practicable technique in a wide range of study organizations (Yokoyama et al, 2020;Hattori et al, 2020). However, one challenge is that the data of our previous reports stated above were obtained from animals maintaining normal homeostasis, and there is a limited information for estimating the microsampling effect on toxicity parameters in animals exhibiting adverse reactions due to drug exposure.…”