1. In rodent studies, microsampling provides an opportunity to sample main study animals for toxicokinetic (TK) assessment rather than using satellite animals. This work compares various potential sampling regimes proposed for the application of microsampling in main study animals with the aim of understanding their performance under increasing inter-individual variability and to assist in assessing the impact of sampling regime on TK interpretation. Using simulations it is may be possible to conclude the most suitable sampling design without conducting costly animal studies. Typically a dose group in a toxicology study contains 10 animals and TK satellite group contains 3 animals per sex. Plasma concentration data is generally analysed using non compartmental analysis (NCA). Composite: collecting a smaller number of sample time points per animal, using all to generate a group profile [1] (Table 1). Serial: collecting all sample time points from single animals to give a number of individual profiles [1]. TK results from satellite group in Table 2 and Figure 1 shows how this was used to simulate the sampling regime options. Performance of Composite and Serial study designs for Estimation of Toxicokinetic Parameters. Teresa Collins (1), Humaira Naseer (1), Brian Middleton (2), Amanda Wilson (1), Jane Stewart (1), Jerome Mettetal (3). (1) Translational Safety, AstraZeneca, Alderley Park, UK, (2) Statistics, AstraZeneca, Alderley Park, UK, (3) Translational Safety, AstraZeneca, Waltham, USA. Methods Aim Conclusion and Learning Results (continued) References Equation 1 Translational Safety [1] Sparrow, S.S.; Robinson, S.; Bolam, S.; Bruce, C.; Danks, A.; Everett, D.; Fulcher, S.; Hill, R.E.; Palmer, H.; Scott, E.W. and Chapman, K.L..Opportunities to minimize animal use in pharmaceutical regulatory general toxicology: A cross-company review. Regulatory Toxicology and Pharmacology. 61 (2011) 222-229. [2]Chapman, K.; Chivers, S.; Gliddon, D.; Mitchell, D.; Robinson, S.;Sangster, T.; Sparrow, S.; Spooner, N. and Wilson, A.. Overcoming the barriers to the uptake of nonclinical microsampling in regulatory safety studies. Drug Discovery Today. 19 (2014) 529-532. [3] Nedelman, J.R. and Jia, X.. An extension of Satherthwaite’s approximation applied to pharmacokinetics. Journal of Biopharmaceutical Statistics. 8(1998), 317-328. [4] Holder, D.. Comments on Nedelman and Jia’s extension of Satterthwaite’s approximation applied to pharmacokinetics. Journal of Biopharmaceutical Statistics. 11 (2001), 75-79 The composite paired design fitted the criteria for calculation of standard error of the AUC [3,4] using NCA but the unpaired did not. Composite designs are complicated to conduct, but sample each animal equally and TK is on pooled data. Serial designs focus on a complete TK profile in a subset of animals and relatively sparse sampling for the remainder. Volume was most variable especially at increasing IIV variability although AUC and Cmax appear more robust in terms of accurate estimation in comparison to the population CL, V and k a. Introducing 50% IIV on Volume resulted in difficulties in obtaining a successful model fit with all sampling designs. In terms of estimating TK parameters (AUC, Cmax) there is no inferiority of the alternative study designs proposed. Since all designs performed reasonably well it cannot be concluded that any particular design is superior to any other proposed here. The simulated data is to be analysed using NCA to see if performance between designs can be further explored. For toxicology studies TK parameters are critical for accurate estimation of safety margins and careful consideration should be given to their estimation. Box plots of the parameter estimates and TK parameters are shown in Figure 2. ParameterEstimateVariance CL (L/hr/kg)7.12- V (L/kg)24.10.0149 k a (h -1 )0.161- Cmax (umol/L)5122- Tmax (h)4.5- AUC (umol*h/L)62967- Error0.143- AUC Tmax Cmax ka V Cl Results DesignTotal samples IIV (%) Successful runsEstimation time (s) Mean (SD) Successful Covariance step Serial n=3 6TP, 2 TP n=7 3210 30 50 1000 0 2.65 (3.33) 21.84 (36.93) 669 574 Serial n=3 6TP, 3 TP n=7 3910 30 50 1000 0 2.70 (3.10) 27.88 (34.84) 717 580 Serial n=3 6TP1810 30 50 1000 976 4.54 (10.93) 9.84(16.11) 888 648 274 Composite n=10 3TP3010 30 50 1000 898 5.05 (9.24) 33.71 (39.15) 24.79 (36.15) 810 536 181 Serial Composite n=10 paired 3TP 3010 30 50 1000 0 6.10 (11.44) 29.88 (28.35) 835 461 Table 1Table 2 Figure 1 Table 3 Figure 2 Parameter estimates on left and absolute signed error (Equation 1) on right. CL, V, k a Cmax, Tmax, AUC