i believe in the pre-clinical trials with healthy volunteers, researchers used Carbon14 to gauge the half-life and paths of elimination during pharmacokinetics studies. it is a common practice. perhaps that is what you are thinking about?
Thanx for your reply - that makes sense. I feel better. I have a lot to learn!
I think their using the the word radioactivity in the context of any of several bodily processes by which substances go out of the body and are eliminated, not a stream of atomic or subatomic particles.
Elimination
"Following administration of a single oral dose of 750 mg 14C-telaprevir in healthy subjects, 90% of total radioactivity was recovered in feces, urine and expired air within 96 hours post-dose. The median recovery of the administered radioactive dose was approximately 82% in the feces, 9% in exhaled air and 1% in urine. The contribution of unchanged 14C-telaprevir and the R-diastereomer of telaprevir towards total radioactivity recovered in feces was 31.9% and 18.8%, respectively. After oral administration, the apparent total clearance (Cl/F) was estimated to be 32.4 L/h with an inter-individual variability of 27.2%. The mean elimination half-life after single-dose oral administration of telaprevir 750 mg typically ranged from about 4.0 to 4.7 hours. At steady state, theeffective half-life is about 9 to 11 hours". .