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Carbon has two stable isotopes, C-12 and C-13. Since they both have the same electronic structure they can both make up the same molecules, but presumably they may perform different functions in biochemistry due to different mass.

Q: Have various stable isotopes of the same atom ever been put to use in pharmacology?

Basic internet research only yielded information about unstable, or radioactive isotopes.

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  • $\begingroup$ I think you'll find that the chemistry is more important than the mass, but I don't know if there has been any pharmaceutical made that that specifically used a stable isotope, so not writing this as an answer. $\endgroup$
    – bob1
    Nov 30, 2023 at 20:00
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    $\begingroup$ @bob1 MRI works on precession of the nuclear spin, and that varies dramatically. Consider 12C (spin 0, no (useful) magnetic moment) vs 13C (spin 1/2 like a proton, but heavier) Now whether medically approved contrast agents used in human MRI are considered a pharmaceutical per se or not is a different question. $\endgroup$
    – uhoh
    Dec 1, 2023 at 7:01
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    $\begingroup$ @uhoh It looks as if the FDA considers them to be intravenous drugs, so, yes, pharmaceuticals $\endgroup$ Dec 1, 2023 at 20:42
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    $\begingroup$ @uhoh I didn't think of contrast agents; wouldn't have thought they are pharma, but apparently they are. $\endgroup$
    – bob1
    Dec 2, 2023 at 8:39

3 Answers 3

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Deutetrabenazine.

As the linked article from Wikipedia notes:

Deutetrabenazine (trade name Austedo) is a vesicular monoamine transporter 2 inhibitor which is used for the treatment of chorea associated with Huntington's disease and tardive dyskinesia.

Chemically, deutetrabenazine is an isotopic isomer of tetrabenazine in which six hydrogen atoms have been replaced by deuterium atoms. The incorporation of deuterium slows the rate of drug metabolism, allowing less frequent dosing.

Whilst what you have in the above is an isotope of hydrogen, the effect this gives is seen in other compounds belonging to the bioisosteres (chemical substituents or groups with similar physical or chemical properties which produce broadly similar biological properties in the same chemical compound), the purpose being to:

enhance the desired biological or physical properties of a compound without making significant changes in chemical structure

The different mass of the deuterium in the case of deutetrabenzine is thought to tweak the chemistry in useful ways:

However, the C–D bond is a bit shorter, and it has reduced electronic polarizability and less hyperconjugative stabilization of adjacent bonds, including developing an anti-bonding orbital as part of the newly formed bond. This can potentially result in weaker van der Waals stabilization, and can produce other changes in properties that are difficult to predict, including changes in the intramolecular volume and the transition state volume

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The urea breath test for Helicobacter pylori uses urea labelled with carbon-13 or carbon-14 to detect the presence of the bacteria, which would metabolize it to carbon dioxide and be exhaled.

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You should check the Wiki articles:

If we solely focus on carbon-13 based drugs then there is carbon-13 labeled ibrutinib, carbon-13 labeled midazolam/1′-hydroxymidazolam, carbon-13 labelled aspirin.

Lastly, you can reads this papers:

  1. Schellekens RC, Stellaard F, Woerdenbag HJ, Frijlink HW, Kosterink JG. Applications of stable isotopes in clinical pharmacology. Br J Clin Pharmacol. 2011 Dec;72(6):879-97. doi: 10.1111/j.1365-2125.2011
  2. Gregg, C.T. Some application of stable isotopes in clinical pharmacology. Eur J Clin Pharmacol 7, 315–319 (1974). DOI: 10.1007/BF00560350
  3. Bodamer OAF, Halliday D, Uses of stable isotopes in clinical diagnosis and research in the paediatric population, Archives of Disease in Childhood 2001;84:444-448, DOI: 10.1136/adc.84.5.444
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