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Mass balance (14C, 3H, 125l, 32P)


To investigate the rate and extent of the excretion of total radioactivity in urine and feces.


Species used for preclinical R&D (no NHP).


In life phase:

Animals are administered with the radio-labeled test item (typical labels: 3H or 14C).

Preliminary experiment for 14C-labeled items:

1 male and 1 female animal is placed into glass metabolic cages and urine, feces and the expired air are collected up to 24h post-dose to exclude the potential loss of the label as expired carbon dioxide.

Main study:

Animals are administered with the radiolabeled test item and placed into plastic metabolic cages.

At scheduled time-points urine and feces samples are collected separately up to maximum 7 days. Cages are washed each 24 hours.


The weight of the collected excreta and cage wash samples are measured, the samples are homogenized and suitable aliquot(s) are subjected to liquid scintillation spectroscopy to quantify the total radioactivity in the samples.

The carcasses are also processed and analyzed, if the average recovery is < 95% of the administered dose at the end of the of the collection period.

For 3H: checking of the potential loss of label due to tritium-proton exchange


Evaluation for the total radioactivity:

  • Concentrations in the collected samples
  • Total amount of radioactivity (as percentage of the administered dose) in the collected fractions
  • Cumulative excretion in relation to time
  • Amount of the non-excreted part of the radioactive dose (radioactivity in the carcasses)
  • Excretion pathway
  • Estimated the absorption, if applicable

On request, selected excreta samples can be stored or transported to dedicated place for further metabolic study.

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