Table 1.
Pharmacokinetic parameters for [131I]PrPSc and [125I]albumin after i.v. injection
| Parameter | [131I]PrPSc | [125I]albumin |
|---|---|---|
| C0 (%ID/ml) | 34.1 ± 9.6 | 130.0 ± 5.9 |
| Distribution t1/2 (min) | 5.44 ± 1.16 | 13.8 ± 5.1 |
| Elimination t1/2 (h) | 3.24 ± 0.45 | 22.6 ± 7.9 |
| Vc (ml) | 4.12 ± 1.31 | 0.78 ± 0.04 |
| Vss (ml) | 11.5 ± 2.5 | 1.32 ± 0.08 |
| CLtot (ml/min) | 0.048 ± 0.010 | 0.0011 ± 0.0004 |
| AUC0-∞ (×103 %ID min/ml) | 2.36 ± 0.33 | 146 ± 50 |
Pharmacokinetic parameters were estimated by fitting a biexponential function (Eq. 1) to serum concentration time curves of each agent. Initial concentration C0 was estimated by the y intercept of the fitted equation and represents the concentration of the agent at time 0. Distribution and elimination serum half-lives t1/2 are estimated by the slopes of the fast (α phase) and slow (β phase) portions of the serum concentration time curve. The fast phase typically corresponds to the distribution of the agent, and the slow phase generally involves the elimination of the agent after distribution. Initial volume of distribution Vc is used to quantify the distribution of the substance throughout the body relatively soon after administration and prior to the material reaching a steady-state equilibrium. Intuitively, the Vc for albumin, the vascular marker, registers the vascular space in tissues. Steady-state volume of distribution Vss estimates the capacity of distribution when the serum concentration of the agent is at constant levels; i.e., when equilibrium of tissue distribution and elimination is reached. Total body clearance CLtot describes how quickly drugs are eliminated, metabolized, or distributed throughout the body. The area under the serum concentration time curve AUC0-∞ estimates total bodily exposure of the agent.