A promotional image for a scientific poster titled "Tritium Radiolabeled Antisense Oligonucleotides for ADME Studies" highlights the importance of absolute bioavailability. It features a preview of the poster, an illustration of molecules, and a "Download Poster Below" button. Branding for "Pharmaron" is visible.

Poster Authors:

J. Bloom, J. Haffenden, D. Price, V. Wilson; Pharmaron UK Ltd, The Old Glassworks, Nettlefold Road, Cardiff, CF24 5JQ, UK

S. Harris, C. Henson , K. Webbley; Pharmaron UK Ltd, Pegasus Way, Crown Business Park, Rushden, NN10 6ER, UK.

H. Beason , G. McMullen, M. Migawa , D. Norris, N. Post; Ionis Pharmaceuticals Inc, 2855 Gazelle Ct. Carlsbad, CA 92010, USA

Radiolabeling is an essential part of drug development. Using a radiolabeled compound, the ADME can be quantitatively determined. Most often carbon-14 is the isotope of choice but tritium is very useful for potent compounds like oligonucleotides. The position of label in the nucleotide must be carefully chosen to avoid exchange in vivo. One also needs to consider the position of the labeled nucleotide in the sequence so that the label is not lost to nuclease-catalysed degradation.