Table 4. Urinary excretion and kinetic parameters for ¹³C-uracil and its metabolites.

Substance	Parameter	50 mg	100 mg	200 mg
13C-uracil	Ae (mg)	0.35 ± 0.19	1.21 ± 0.80	4.52 ± 2.80
	CLR (l h−1)	6.8 ± 1.6	7.2 ± 2.1	7.7 ± 1.4
	Excretion (%/dose)	0.7 ± 0.4	1.2 ± 0.8	2.3 ± 1.4
13C-DHU	Ae (mg)	0.10 ± 0.05	0.28 ± 0.14	0.83 ± 0.44
	CLR (l h−1)	0.7 ± 0.2	0.7 ± 0.2	0.8 ± 0.3
	Excretion (%/dose)	0.2 ± 0.1	0.3 ± 0.1	0.4 ± 0.2
13C-UPA	Ae (mg)	0.21 ± 0.10	0.53 ± 0.31	1.33 ± 0.91
	CLR (l h−1)	17.1 ± 8.7	13.4 ± 6.3	9.1 ± 4.1
	Excretion (%/dose)	0.4 ± 0.2	0.5 ± 0.3	0.6 ± 0.4

¹³C-DHU: 5,6-dihydrouracil (2-¹³C)]¹³C-UPA,β-ureidopropionic acid (ureido-¹³C). Values: mean ± SD (n = 12).